[java] Intro openApiNullable property to enable/disable OpenAPI Jackson Nullable library (#6154)

* Add option to prevent usage of jackson-nullable (#2901)

Add a option for all java client and server to prevent
usage of third party library (jackson-databind-nullable)
which may be forbidden in some company

Add samples for Vertx, Spring MVC, Spring Cloud, Feign and Play

Upgrade dependencies for org.openapitools:jackson-databind-nullable

* Samples - Remove dependency org.openapitools:jackson-databind-nullable (#2901)

* Fix generation of gradle file for vertx (#2901)

* Regenerate samples (#2901)

* Fix documentation and up to date (#2901)

* Fix forgotten regeneration of vertx after dependency integration (#2901)

* Regenerate template after rebase (#2901)

* Use yaml config files introduce in #6509 to manage samples (#2901)

* Regenerate template using the config (#2901)

* Fix bad version during testing generated samples (#2901)

* Regenerate template after fix bad version (#2901)

* Fix merge, allow for set importing on codegen model

Co-authored-by: Jim Schubert <james.schubert@gmail.com>

bin/configs/java-feign-no-nullable.yaml

@@ -0,0 +1,11 @@
+generatorName: java
+outputDir: samples/client/petstore/java/feign-no-nullable
+library: feign
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  booleanGetterPrefix: is
+  artifactId: petstore-feign-no-nullable
+  hideGenerationTimestamp: "true"
+  additionalModelTypeAnnotations: '@javax.annotation.concurrent.Immutable'
+  openApiNullable: "false"

bin/configs/java-play-framework-no-nullable.yaml

@@ -0,0 +1,7 @@
+generatorName: java-play-framework
+outputDir: samples/server/petstore/java-play-framework-no-nullable
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore.yaml
+templateDir: modules/openapi-generator/src/main/resources/JavaPlayFramework
+additionalProperties:
+  hideGenerationTimestamp: "true"
+  openApiNullable: "false"

bin/configs/java-vertx-no-nullable.yaml

@@ -0,0 +1,9 @@
+generatorName: java
+outputDir: samples/client/petstore/java/vertx-no-nullable
+library: vertx
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/Java
+additionalProperties:
+  artifactId: petstore-vertx-no-nullable
+  hideGenerationTimestamp: "true"
+  openApiNullable: "false"

bin/configs/spring-boot-beanvalidation-no-nullable.yaml

@@ -0,0 +1,11 @@
+generatorName: spring
+outputDir: samples/server/petstore/springboot-beanvalidation-no-nullable
+library: spring-boot
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/JavaSpring
+additionalProperties:
+  java8: "false"
+  useBeanValidation: true
+  artifactId: spring-boot-beanvalidation-no-nullable
+  hideGenerationTimestamp: "true"
+  openApiNullable: "false"

bin/configs/spring-cloud-no-nullable.yaml

@@ -0,0 +1,10 @@
+generatorName: spring
+outputDir: samples/client/petstore/spring-cloud-no-nullable
+library: spring-cloud
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore.yaml
+templateDir: modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-cloud
+additionalProperties:
+  artifactId: petstore-spring-cloud-no-nullable
+  responseWrapper: HystrixCommand
+  hideGenerationTimestamp: "true"
+  openApiNullable: "false"

bin/configs/spring-mvc-no-nullable.yaml

@@ -0,0 +1,10 @@
+generatorName: spring
+outputDir: samples/server/petstore/spring-mvc-no-nullable
+library: spring-mvc
+inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore-with-fake-endpoints-models-for-testing.yaml
+templateDir: modules/openapi-generator/src/main/resources/JavaSpring
+additionalProperties:
+  artifactId: spring-mvc-server-no-nullable
+  openApiNullable: "false"
+  serverPort: "8002"
+  hideGenerationTimestamp: "true"

docs/generators/groovy.md

@@ -30,6 +30,7 @@ sidebar_label: groovy
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-inflector.md

@@ -32,6 +32,7 @@ sidebar_label: java-inflector
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-msf4j.md

@@ -34,6 +34,7 @@ sidebar_label: java-msf4j
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-pkmst.md

@@ -34,6 +34,7 @@ sidebar_label: java-pkmst
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |com.prokarma.pkmst.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-play-framework.md

@@ -36,6 +36,7 @@ sidebar_label: java-play-framework
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |apimodels|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-undertow-server.md

@@ -32,6 +32,7 @@ sidebar_label: java-undertow-server
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |null|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-vertx-web.md

@@ -32,6 +32,7 @@ sidebar_label: java-vertx-web
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.vertxweb.server.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java-vertx.md

@@ -32,6 +32,7 @@ sidebar_label: java-vertx
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.server.api.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/java.md

@@ -36,6 +36,7 @@ sidebar_label: java
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |microprofileFramework|Framework for microprofile. Possible values "kumuluzee"| |null|
 |modelPackage|package for generated models| |org.openapitools.client.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parcelableModel|Whether to generate models for Android that implement Parcelable with the okhttp-gson library.| |false|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-cxf-cdi.md

@@ -37,6 +37,7 @@ sidebar_label: jaxrs-cxf-cdi
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |openApiSpecFileLocation|Location where the file containing the spec will be generated in the output folder. No file generated when set to null or empty string.| |null|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-cxf-client.md

@@ -32,6 +32,7 @@ sidebar_label: jaxrs-cxf-client
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-cxf-extended.md

@@ -40,6 +40,7 @@ sidebar_label: jaxrs-cxf-extended
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |loadTestDataFromFile|Load test data from a generated JSON file| |false|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-cxf.md

@@ -38,6 +38,7 @@ sidebar_label: jaxrs-cxf
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-jersey.md

@@ -34,6 +34,7 @@ sidebar_label: jaxrs-jersey
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-resteasy-eap.md

@@ -34,6 +34,7 @@ sidebar_label: jaxrs-resteasy-eap
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-resteasy.md

@@ -34,6 +34,7 @@ sidebar_label: jaxrs-resteasy
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/jaxrs-spec.md

@@ -37,6 +37,7 @@ sidebar_label: jaxrs-spec
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |openApiSpecFileLocation|Location where the file containing the spec will be generated in the output folder. No file generated when set to null or empty string.| |null|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

docs/generators/spring.md

@@ -41,6 +41,7 @@ sidebar_label: spring
 |licenseName|The name of the license| |Unlicense|
 |licenseUrl|The URL of the license| |http://unlicense.org|
 |modelPackage|package for generated models| |org.openapitools.model|
+|openApiNullable|Enable OpenAPI Jackson Nullable library| |true|
 |parentArtifactId|parent artifactId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentGroupId|parent groupId in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|
 |parentVersion|parent version in generated pom N.B. parentGroupId, parentArtifactId and parentVersion must all be specified for any of them to take effect| |null|

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AbstractJavaCodegen.java

@@ -61,6 +61,7 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
     public static final String BOOLEAN_GETTER_PREFIX = "booleanGetterPrefix";
     public static final String ADDITIONAL_MODEL_TYPE_ANNOTATIONS = "additionalModelTypeAnnotations";
     public static final String DISCRIMINATOR_CASE_SENSITIVE = "discriminatorCaseSensitive";
+    public static final String OPENAPI_NULLABLE = "openApiNullable";
 
     protected String dateLibrary = "threetenbp";
     protected boolean supportAsync = false;
@@ -100,6 +101,7 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
     protected String parentVersion = "";
     protected boolean parentOverridden = false;
     protected List<String> additionalModelTypeAnnotations = new LinkedList<>();
+    protected boolean openApiNullable = true;
 
     public AbstractJavaCodegen() {
         super();
@@ -218,6 +220,7 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         cliOptions.add(CliOption.newBoolean(DISABLE_HTML_ESCAPING, "Disable HTML escaping of JSON strings when using gson (needed to avoid problems with byte[] fields)", disableHtmlEscaping));
         cliOptions.add(CliOption.newString(BOOLEAN_GETTER_PREFIX, "Set booleanGetterPrefix").defaultValue(this.getBooleanGetterPrefix()));
         cliOptions.add(CliOption.newString(ADDITIONAL_MODEL_TYPE_ANNOTATIONS, "Additional annotations for model type(class level annotations)"));
+        cliOptions.add(CliOption.newBoolean(OPENAPI_NULLABLE, "Enable OpenAPI Jackson Nullable library", this.openApiNullable));
 
         cliOptions.add(CliOption.newString(CodegenConstants.PARENT_GROUP_ID, CodegenConstants.PARENT_GROUP_ID_DESC));
         cliOptions.add(CliOption.newString(CodegenConstants.PARENT_ARTIFACT_ID, CodegenConstants.PARENT_ARTIFACT_ID_DESC));
@@ -412,6 +415,11 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         }
         additionalProperties.put(WITH_XML, withXml);
 
+        if (additionalProperties.containsKey(OPENAPI_NULLABLE)) {
+            this.setOpenApiNullable(Boolean.valueOf(additionalProperties.get(OPENAPI_NULLABLE).toString()));
+        }
+        additionalProperties.put(OPENAPI_NULLABLE, openApiNullable);
+
         if (additionalProperties.containsKey(CodegenConstants.PARENT_GROUP_ID)) {
             this.setParentGroupId((String) additionalProperties.get(CodegenConstants.PARENT_GROUP_ID));
         }
@@ -1507,6 +1515,14 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         this.booleanGetterPrefix = booleanGetterPrefix;
     }
 
+    public boolean isOpenApiNullable() {
+        return openApiNullable;
+    }
+
+    public void setOpenApiNullable(final boolean openApiNullable) {
+        this.openApiNullable = openApiNullable;
+    }
+
     @Override
     public String escapeQuotationMark(String input) {
         // remove " to avoid code injection

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/JavaClientCodegen.java

@@ -779,11 +779,14 @@ public class JavaClientCodegen extends AbstractJavaCodegen
                 Map<String, Object> mo = (Map<String, Object>) _mo;
                 CodegenModel cm = (CodegenModel) mo.get("model");
                 boolean addImports = false;
+
                 for (CodegenProperty var : cm.vars) {
+                    if (this.openApiNullable) {
                         boolean isOptionalNullable = Boolean.FALSE.equals(var.required) && Boolean.TRUE.equals(var.isNullable);
                         // only add JsonNullable and related imports to optional and nullable values
                         addImports |= isOptionalNullable;
                         var.getVendorExtensions().put("x-is-jackson-optional-nullable", isOptionalNullable);
+                    }
 
                     if (Boolean.TRUE.equals(var.getVendorExtensions().get("x-enum-as-string"))) {
                         // treat enum string as just string
@@ -808,6 +811,7 @@ public class JavaClientCodegen extends AbstractJavaCodegen
                         importsHashSet.put("import", "java.util.HashSet");
                         imports.add(importsHashSet);
                     }
+
                 }
 
                 if (addImports) {
@@ -824,7 +828,6 @@ public class JavaClientCodegen extends AbstractJavaCodegen
                     }
                 }
             }
-        }
 
             // add implements for serializable/parcelable to all models
             for (Object _mo : models) {
@@ -854,6 +857,7 @@ public class JavaClientCodegen extends AbstractJavaCodegen
                     ((ArrayList<String>) cm.getVendorExtensions().get("x-implements")).add("Serializable");
                 }
             }
+        }
 
         return objs;
     }
@@ -951,8 +955,6 @@ public class JavaClientCodegen extends AbstractJavaCodegen
         setSerializationLibrary(serializationLibrary);
     }
 
-
-
     @Override
     public Map<String, Object> postProcessSupportingFileData(Map<String, Object> objs) {
         generateYAMLSpecFile(objs);

modules/openapi-generator/src/main/resources/Java/build.gradle.mustache

@@ -138,7 +138,9 @@ ext {
     swagger_annotations_version = "1.5.22"
     jackson_version = "2.10.3"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     {{#threetenbp}}
     jackson_threetenbp_version = "2.9.10"
     {{/threetenbp}}
@@ -156,7 +158,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
     compile "com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:$jackson_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#joda}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-joda:$jackson_version"
     {{/joda}}

modules/openapi-generator/src/main/resources/Java/libraries/feign/ApiClient.mustache

@@ -15,7 +15,9 @@ import org.threeten.bp.*;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{#joda}}
 import com.fasterxml.jackson.datatype.joda.JodaModule;
 {{/joda}}
@@ -181,8 +183,10 @@ public class ApiClient {
     module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
     objectMapper.registerModule(module);
     {{/threetenbp}}
+    {{#openApiNullable}}
     JsonNullableModule jnm = new JsonNullableModule();
     objectMapper.registerModule(jnm);
+    {{/openApiNullable}}
     return objectMapper;
   }
 

modules/openapi-generator/src/main/resources/Java/libraries/feign/build.gradle.mustache

@@ -122,7 +122,9 @@ ext {
     swagger_annotations_version = "1.5.24"
     jackson_version = "2.10.3"
     jackson_databind_version = "2.10.3"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     {{#threetenbp}}
     jackson_threetenbp_version = "2.9.10"
     {{/threetenbp}}
@@ -142,7 +144,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-core:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#joda}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-joda:$jackson_version"
     {{/joda}}

modules/openapi-generator/src/main/resources/Java/libraries/feign/pom.mustache

@@ -274,11 +274,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-databind-version}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         {{#withXml}}
 
             <!-- XML Support -->
@@ -351,7 +353,9 @@
         <feign-version>10.11</feign-version>
         <feign-form-version>3.8.0</feign-form-version>
         <jackson-version>2.10.3</jackson-version>
+        {{#openApiNullable}}
         <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
+        {{/openApiNullable}}
         <jackson-databind-version>2.10.3</jackson-databind-version>
         {{#threetenbp}}
         <jackson-threetenbp-version>2.9.10</jackson-threetenbp-version>

modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/ApiClient.mustache

@@ -4,7 +4,9 @@ import {{apiPackage}}.*;
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{#joda}}
 import com.fasterxml.jackson.datatype.joda.JodaModule;
 {{/joda}}
@@ -54,8 +56,10 @@ public class ApiClient {
         module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
         objectMapper.registerModule(module);
         {{/threetenbp}}
+        {{#openApiNullable}}
         JsonNullableModule jnm = new JsonNullableModule();
         objectMapper.registerModule(jnm);
+        {{/openApiNullable}}
         return objectMapper;
     }
 

modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/build.gradle.mustache

@@ -122,7 +122,9 @@ ext {
     swagger_annotations_version = "1.5.22"
     jackson_version = "2.10.1"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     google_api_client_version = "1.23.0"
     jersey_common_version = "2.25.1"
     jodatime_version = "2.9.9"
@@ -141,7 +143,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
     compile "com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:$jackson_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#java8}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$jackson_version"
     {{/java8}}

modules/openapi-generator/src/main/resources/Java/libraries/google-api-client/pom.mustache

@@ -267,11 +267,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-version}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         {{#withXml}}
             <!-- XML processing: Jackson -->
             <dependency>
@@ -328,7 +330,9 @@
         <jersey-common-version>2.25.1</jersey-common-version>
         <jackson-version>2.10.4</jackson-version>
         <jackson-databind-version>2.10.4</jackson-databind-version>
+        {{#openApiNullable}}
         <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
+        {{/openApiNullable}}
         {{#joda}}
         <jodatime-version>2.9.9</jodatime-version>
         {{/joda}}

modules/openapi-generator/src/main/resources/Java/libraries/jersey2/JSON.mustache

@@ -5,7 +5,9 @@ import org.threeten.bp.*;
 {{/threetenbp}}
 import com.fasterxml.jackson.annotation.*;
 import com.fasterxml.jackson.databind.*;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{#java8}}
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 {{/java8}}
@@ -54,8 +56,10 @@ public class JSON implements ContextResolver<ObjectMapper> {
     module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
     mapper.registerModule(module);
     {{/threetenbp}}
+    {{#openApiNullable}}
     JsonNullableModule jnm = new JsonNullableModule();
     mapper.registerModule(jnm);
+    {{/openApiNullable}}
   }
 
   /**

modules/openapi-generator/src/main/resources/Java/libraries/jersey2/build.gradle.mustache

@@ -121,7 +121,9 @@ ext {
     swagger_annotations_version = "1.5.22"
     jackson_version = "2.10.3"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     {{#supportJava6}}
     jersey_version = "2.6"
     commons_io_version=2.5
@@ -152,7 +154,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-core:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#joda}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-joda:$jackson_version"
     {{/joda}}

modules/openapi-generator/src/main/resources/Java/libraries/jersey2/pom.mustache

@@ -296,11 +296,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-databind-version}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         {{#withXml}}
         <!-- XML processing: JAXB -->
         <dependency>

modules/openapi-generator/src/main/resources/Java/libraries/native/ApiClient.mustache

@@ -6,7 +6,9 @@ import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 
 import java.io.InputStream;
 import java.net.URI;
@@ -155,8 +157,10 @@ public class ApiClient {
     mapper.enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING);
     mapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING);
     mapper.registerModule(new JavaTimeModule());
+    {{#openApiNullable}}
     JsonNullableModule jnm = new JsonNullableModule();
     mapper.registerModule(jnm);
+    {{/openApiNullable}}
     URI baseURI = URI.create("{{{basePath}}}");
     scheme = baseURI.getScheme();
     host = baseURI.getHost();

modules/openapi-generator/src/main/resources/Java/libraries/rest-assured/JacksonObjectMapper.mustache

@@ -7,7 +7,9 @@ import org.threeten.bp.*;
 {{/threetenbp}}
 import com.fasterxml.jackson.annotation.*;
 import com.fasterxml.jackson.databind.*;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{#java8}}
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 {{/java8}}
@@ -52,8 +54,10 @@ public class JacksonObjectMapper extends Jackson2Mapper {
             module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
             mapper.registerModule(module);
             {{/threetenbp}}
+            {{#openApiNullable}}
             JsonNullableModule jnm = new JsonNullableModule();
             mapper.registerModule(jnm);
+            {{/openApiNullable}}
             return mapper;
         };
     }

modules/openapi-generator/src/main/resources/Java/libraries/rest-assured/build.gradle.mustache

@@ -101,7 +101,9 @@ ext {
 {{#jackson}}
     jackson_version = "2.10.3"
     jackson_databind_version = "2.10.3"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     {{#threetenbp}}
     jackson_threetenbp_version = "2.10.0"
     {{/threetenbp}}
@@ -128,7 +130,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
     compile "com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:$jackson_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#withXml}}
     compile "com.fasterxml.jackson.dataformat:jackson-dataformat-xml:$jackson_version"
     {{/withXml}}

modules/openapi-generator/src/main/resources/Java/libraries/rest-assured/build.sbt.mustache

@@ -17,7 +17,9 @@ lazy val root = (project in file(".")).
       "com.fasterxml.jackson.core" % "jackson-core" % "2.10.3",
       "com.fasterxml.jackson.core" % "jackson-annotations" % "2.10.3",
       "com.fasterxml.jackson.core" % "jackson-databind" % "2.10.3",
+      {{#openApiNullable}}
       "org.openapitools" % "jackson-databind-nullable" % "0.2.1",
+      {{/openApiNullable}}
       {{#withXml}}
       "com.fasterxml.jackson.dataformat" % "jackson-dataformat-xml" % "2.10.3",
       {{/withXml}}

modules/openapi-generator/src/main/resources/Java/libraries/resteasy/JSON.mustache

@@ -2,7 +2,9 @@ package {{invokerPackage}};
 
 import com.fasterxml.jackson.annotation.*;
 import com.fasterxml.jackson.databind.*;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{#java8}}
 import com.fasterxml.jackson.datatype.jsr310.*;
 {{/java8}}
@@ -27,8 +29,10 @@ public class JSON implements ContextResolver<ObjectMapper> {
     mapper.enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING);
     mapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING);
     mapper.setDateFormat(new RFC3339DateFormat());
+    {{#openApiNullable}}
     JsonNullableModule jnm = new JsonNullableModule();
     mapper.registerModule(jnm);
+    {{/openApiNullable}}
     {{#java8}}
     mapper.registerModule(new JavaTimeModule());
     {{/java8}}

modules/openapi-generator/src/main/resources/Java/libraries/resteasy/build.gradle.mustache

@@ -121,7 +121,9 @@ ext {
     swagger_annotations_version = "1.5.22"
     jackson_version = "2.10.4"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     threetenbp_version = "2.9.10"
     resteasy_version = "3.1.3.Final"
     {{^java8}}
@@ -144,7 +146,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
     compile "com.github.joschi.jackson:jackson-datatype-threetenbp:$threetenbp_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#java8}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$jackson_version"
     {{/java8}}

modules/openapi-generator/src/main/resources/Java/libraries/resteasy/pom.mustache

@@ -226,11 +226,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-databind-version}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         {{#withXml}}
 
         <!-- XML processing: Jackson -->

modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/ApiClient.mustache

@@ -39,7 +39,9 @@ import com.fasterxml.jackson.datatype.threetenbp.ThreeTenModule;
 import org.springframework.http.converter.HttpMessageConverter;
 import org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter;
 import com.fasterxml.jackson.databind.ObjectMapper;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 {{/threetenbp}}
 
 import java.io.BufferedReader;
@@ -702,7 +704,9 @@ public class ApiClient {
         messageConverters.add(new MappingJackson2HttpMessageConverter());
         XmlMapper xmlMapper = new XmlMapper();
         xmlMapper.configure(ToXmlGenerator.Feature.WRITE_XML_DECLARATION, true);
+        {{#openApiNullable}}
         xmlMapper.registerModule(new JsonNullableModule());
+        {{/openApiNullable}}
         messageConverters.add(new MappingJackson2XmlHttpMessageConverter(xmlMapper));
 
         RestTemplate restTemplate = new RestTemplate(messageConverters);
@@ -716,7 +720,9 @@ public class ApiClient {
                 module.addDeserializer(OffsetDateTime.class, CustomInstantDeserializer.OFFSET_DATE_TIME);
                 module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
                 mapper.registerModule(module);
+                {{#openApiNullable}}
                 mapper.registerModule(new JsonNullableModule());
+                {{/openApiNullable}}
             }
         }
         {{/threetenbp}}

modules/openapi-generator/src/main/resources/Java/libraries/resttemplate/build.gradle.mustache

@@ -122,7 +122,9 @@ ext {
     swagger_annotations_version = "1.5.22"
     jackson_version = "2.10.4"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     spring_web_version = "5.2.5.RELEASE"
     jodatime_version = "2.9.9"
     junit_version = "4.13"
@@ -140,7 +142,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
     compile "com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:$jackson_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     {{#java8}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$jackson_version"
     {{/java8}}

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/build.gradle.mustache

@@ -124,7 +124,9 @@ ext {
     {{#usePlayWS}}
     jackson_version = "2.10.4"
     jackson_databind_version = "2.10.4"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
     {{#play24}}
     play_version = "2.4.11"
     {{/play24}}
@@ -195,7 +197,9 @@ dependencies {
     compile "com.fasterxml.jackson.core:jackson-core:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
     compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     compile "com.fasterxml.jackson.datatype:jackson-datatype-{{^java8}}joda{{/java8}}{{#java8}}jsr310{{/java8}}:$jackson_version"
     {{/usePlayWS}}
     compile 'javax.annotation:javax.annotation-api:1.3.2'

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/play24/ApiClient.mustache

@@ -9,7 +9,9 @@ import retrofit2.Retrofit;
 import retrofit2.converter.scalars.ScalarsConverterFactory;
 import retrofit2.converter.jackson.JacksonConverterFactory;
 import com.fasterxml.jackson.databind.ObjectMapper;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 
 import play.libs.Json;
 import play.libs.ws.WSClient;
@@ -72,8 +74,10 @@ public class ApiClient {
         }
 
         ObjectMapper mapper = Json.mapper();
+        {{#openApiNullable}}
         JsonNullableModule jnm = new JsonNullableModule();
         mapper.registerModule(jnm);
+        {{/openApiNullable}}
 
         return new Retrofit.Builder()
                        .baseUrl(basePath)

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/play25/ApiClient.mustache

@@ -9,7 +9,9 @@ import retrofit2.Retrofit;
 import retrofit2.converter.scalars.ScalarsConverterFactory;
 import retrofit2.converter.jackson.JacksonConverterFactory;
 import com.fasterxml.jackson.databind.ObjectMapper;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 
 import play.libs.Json;
 import play.libs.ws.WSClient;
@@ -71,8 +73,10 @@ public class ApiClient {
         }
 
         ObjectMapper mapper = Json.mapper();
+        {{#openApiNullable}}
         JsonNullableModule jnm = new JsonNullableModule();
         mapper.registerModule(jnm);
+        {{/openApiNullable}}
 
         return new Retrofit.Builder()
                        .baseUrl(basePath)

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/play26/ApiClient.mustache

@@ -13,7 +13,9 @@ import retrofit2.Converter;
 import retrofit2.Retrofit;
 import retrofit2.converter.scalars.ScalarsConverterFactory;
 import retrofit2.converter.jackson.JacksonConverterFactory;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 
 import play.libs.Json;
 import play.libs.ws.WSClient;
@@ -91,8 +93,10 @@ public class ApiClient {
         }
         if (defaultMapper == null) {
             defaultMapper = Json.mapper();
+            {{#openApiNullable}}
             JsonNullableModule jnm = new JsonNullableModule();
             defaultMapper.registerModule(jnm);
+            {{/openApiNullable}}
         }
 
         return new Retrofit.Builder()

modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/pom.mustache

@@ -342,11 +342,13 @@
                 <artifactId>jackson-databind</artifactId>
                 <version>${jackson-version}</version>
             </dependency>
+            {{#openApiNullable}}
             <dependency>
                 <groupId>org.openapitools</groupId>
                 <artifactId>jackson-databind-nullable</artifactId>
                 <version>${jackson-databind-nullable-version}</version>
             </dependency>
+            {{/openApiNullable}}
             <dependency>
                 <groupId>com.fasterxml.jackson.datatype</groupId>
                 <artifactId>jackson-datatype-{{^java8}}joda{{/java8}}{{#java8}}jsr310{{/java8}}</artifactId>
@@ -428,7 +430,9 @@
         {{#play26}}
         <play-version>2.6.7</play-version>
         {{/play26}}
+        {{#openApiNullable}}
         <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
+        {{/openApiNullable}}
         {{/usePlayWS}}
         <retrofit-version>2.5.0</retrofit-version>
         {{#useRxJava}}

modules/openapi-generator/src/main/resources/Java/libraries/vertx/ApiClient.mustache

@@ -15,7 +15,9 @@ import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 import io.vertx.core.*;
 import io.vertx.core.buffer.Buffer;
 import io.vertx.core.file.AsyncFile;
@@ -81,8 +83,10 @@ public class ApiClient {
         this.objectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING);
         this.objectMapper.registerModule(new JavaTimeModule());
         this.objectMapper.setDateFormat(dateFormat);
+        {{#openApiNullable}}
         JsonNullableModule jnm = new JsonNullableModule();
         this.objectMapper.registerModule(jnm);
+        {{/openApiNullable}}
 
         // Setup authentications (key: authentication name, value: authentication).
         this.authentications = new HashMap<>();{{#authMethods}}{{#isBasic}}{{#isBasicBasic}}

modules/openapi-generator/src/main/resources/Java/libraries/vertx/build.gradle.mustache

@@ -32,7 +32,12 @@ ext {
     jackson_databind_version = "2.10.4"
     vertx_version = "3.4.2"
     junit_version = "4.13"
+    {{#openApiNullable}}
     jackson_databind_nullable_version = "0.2.1"
+    {{/openApiNullable}}
+    {{#threetenbp}}
+    jackson_threeten_version = "2.9.10"
+    {{/threetenbp}}
 }
 
 dependencies {
@@ -50,9 +55,11 @@ dependencies {
     compile "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$jackson_version"
     {{/java8}}
     {{#threetenbp}}
-    compile "com.github.joschi.jackson:jackson-datatype-threetenbp:$jackson_version"
+    compile "com.github.joschi.jackson:jackson-datatype-threetenbp:jackson_threeten_version"
     {{/threetenbp}}
+    {{#openApiNullable}}
     compile "org.openapitools:jackson-databind-nullable:$jackson_databind_nullable_version"
+    {{/openApiNullable}}
     compile 'javax.annotation:javax.annotation-api:1.3.2'
     testCompile "junit:junit:$junit_version"
     testCompile "io.vertx:vertx-unit:$vertx_version"

modules/openapi-generator/src/main/resources/Java/libraries/vertx/pom.mustache

@@ -257,11 +257,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-databind}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         {{#joda}}
             <dependency>
                 <groupId>com.fasterxml.jackson.datatype</groupId>

modules/openapi-generator/src/main/resources/Java/libraries/webclient/ApiClient.mustache

@@ -3,7 +3,9 @@ package {{invokerPackage}};
 import com.fasterxml.jackson.databind.DeserializationFeature;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.springframework.core.ParameterizedTypeReference;
@@ -98,8 +100,10 @@ public class ApiClient {
         mapper.setDateFormat(dateFormat);
         mapper.registerModule(new JavaTimeModule());
         mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+        {{#openApiNullable}}
         JsonNullableModule jnm = new JsonNullableModule();
         mapper.registerModule(jnm);
+        {{/openApiNullable}}
 
         this.webClient = buildWebClient(mapper);
         this.init();

modules/openapi-generator/src/main/resources/Java/libraries/webclient/pom.mustache

@@ -105,11 +105,13 @@
             <artifactId>jackson-databind</artifactId>
             <version>${jackson-databind-version}</version>
         </dependency>
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
 
         {{#java8}}
             <dependency>

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-boot/openapi2SpringBoot.mustache

@@ -1,7 +1,9 @@
 package {{basePackage}};
 
 import com.fasterxml.jackson.databind.Module;
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 import org.springframework.boot.CommandLineRunner;
 import org.springframework.boot.ExitCodeGenerator;
 import org.springframework.boot.SpringApplication;
@@ -71,9 +73,11 @@ public class OpenAPI2SpringBoot implements CommandLineRunner {
         };
     }
 
+{{#openApiNullable}}
     @Bean
     public Module jsonNullableModule() {
         return new JsonNullableModule();
     }
+{{/openApiNullable}}
 
 }

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-boot/pom.mustache

@@ -148,11 +148,13 @@
             <version>2.8.4</version>
         </dependency>
         {{/threetenbp}}
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
             <version>0.2.1</version>
         </dependency>
+        {{/openApiNullable}}
 {{#useBeanValidation}}
     <!-- Bean Validation API support -->
         <dependency>

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-cloud/pom.mustache

@@ -93,6 +93,7 @@
         {{/parentOverridden}}
         </dependency>
         {{/threetenbp}}
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
@@ -100,6 +101,7 @@
             <version>0.1.0</version>
             {{/parentOverridden}}
         </dependency>
+        {{/openApiNullable}}
         <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-starter-test</artifactId>

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-mvc/openapiUiConfiguration.mustache

@@ -5,7 +5,9 @@ import com.fasterxml.jackson.databind.SerializationFeature;
 {{#threetenbp}}
 import com.fasterxml.jackson.datatype.threetenbp.ThreeTenModule;
 {{/threetenbp}}
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullableModule;
+{{/openApiNullable}}
 import org.springframework.context.annotation.ComponentScan;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.PropertySource;
@@ -95,7 +97,8 @@ public class OpenAPIUiConfiguration extends WebMvcConfigurerAdapter {
     return new Jackson2ObjectMapperBuilder()
         .indentOutput(true)
         .featuresToDisable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS)
-        .modulesToInstall({{#threetenbp}}module, {{/threetenbp}}new JsonNullableModule())
+        {{#openApiNullable}}.modulesToInstall({{#threetenbp}}module, {{/threetenbp}}new JsonNullableModule()){{/openApiNullable}}
+        {{^openApiNullable}}{{#threetenbp}}.modulesToInstall(module){{/threetenbp}}{{/openApiNullable}}
         .dateFormat(new RFC3339DateFormat());
   }
 

modules/openapi-generator/src/main/resources/JavaSpring/libraries/spring-mvc/pom.mustache

@@ -218,11 +218,13 @@
             <version>${jackson-threetenbp-version}</version>
         </dependency>
         {{/threetenbp}}
+        {{#openApiNullable}}
         <dependency>
             <groupId>org.openapitools</groupId>
             <artifactId>jackson-databind-nullable</artifactId>
-            <version>0.1.0</version>
+            <version>${jackson-databind-nullable-version}</version>
         </dependency>
+        {{/openApiNullable}}
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
@@ -267,5 +269,8 @@
         <beanvalidation-version>1.1.0.Final</beanvalidation-version>
 {{/useBeanValidation}}
         <spring-version>4.3.20.RELEASE</spring-version>
+        {{#openApiNullable}}
+        <jackson-databind-nullable-version>0.2.1</jackson-databind-nullable-version>
+        {{/openApiNullable}}
     </properties>
 </project>

modules/openapi-generator/src/main/resources/JavaSpring/model.mustache

@@ -3,7 +3,9 @@ package {{package}};
 import java.util.Objects;
 {{#imports}}import {{import}};
 {{/imports}}
+{{#openApiNullable}}
 import org.openapitools.jackson.nullable.JsonNullable;
+{{/openApiNullable}}
 {{#serializableModel}}
 import java.io.Serializable;
 {{/serializableModel}}

modules/openapi-generator/src/main/resources/JavaSpring/nullableDataType.mustache

@@ -1 +1 @@
-{{#isNullable}}JsonNullable<{{{datatypeWithEnum}}}>{{/isNullable}}{{^isNullable}}{{{datatypeWithEnum}}}{{/isNullable}}
+{{#openApiNullable}}{{#isNullable}}JsonNullable<{{{datatypeWithEnum}}}>{{/isNullable}}{{^isNullable}}{{{datatypeWithEnum}}}{{/isNullable}}{{/openApiNullable}}{{^openApiNullable}}{{{datatypeWithEnum}}}{{/openApiNullable}}

modules/openapi-generator/src/main/resources/JavaSpring/pojo.mustache

@@ -28,7 +28,12 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}}{{^parent}}
   {{/gson}}
   {{#isContainer}}
   {{#useBeanValidation}}@Valid{{/useBeanValidation}}
+  {{#openApiNullable}}
   private {{>nullableDataType}} {{name}} = {{#isNullable}}JsonNullable.undefined(){{/isNullable}}{{^isNullable}}{{#required}}{{{defaultValue}}}{{/required}}{{^required}}null{{/required}}{{/isNullable}};
+  {{/openApiNullable}}
+  {{^openApiNullable}}
+  private {{>nullableDataType}} {{name}} = {{#required}}{{{defaultValue}}}{{/required}}{{^required}}null{{/required}};
+  {{/openApiNullable}}
   {{/isContainer}}
   {{^isContainer}}
   {{#isDate}}
@@ -37,24 +42,42 @@ public class {{classname}} {{#parent}}extends {{{parent}}}{{/parent}}{{^parent}}
   {{#isDateTime}}
   @org.springframework.format.annotation.DateTimeFormat(iso = org.springframework.format.annotation.DateTimeFormat.ISO.DATE_TIME)
   {{/isDateTime}}
+  {{#openApiNullable}}
   private {{>nullableDataType}} {{name}}{{#isNullable}} = JsonNullable.undefined(){{/isNullable}}{{^isNullable}}{{#defaultValue}} = {{{.}}}{{/defaultValue}}{{/isNullable}};
+  {{/openApiNullable}}
+  {{^openApiNullable}}
+  private {{>nullableDataType}} {{name}}{{#isNullable}} = null{{/isNullable}}{{^isNullable}}{{#defaultValue}} = {{{.}}}{{/defaultValue}}{{/isNullable}};
+  {{/openApiNullable}}
   {{/isContainer}}
 
   {{/vars}}
   {{#vars}}
   public {{classname}} {{name}}({{{datatypeWithEnum}}} {{name}}) {
+    {{#openApiNullable}}
     this.{{name}} = {{#isNullable}}JsonNullable.of({{name}}){{/isNullable}}{{^isNullable}}{{name}}{{/isNullable}};
+    {{/openApiNullable}}
+    {{^openApiNullable}}
+    this.{{name}} = {{name}};
+    {{/openApiNullable}}
     return this;
   }
   {{#isListContainer}}
 
   public {{classname}} add{{nameInCamelCase}}Item({{{items.datatypeWithEnum}}} {{name}}Item) {
+    {{#openApiNullable}}
     {{^required}}
     if (this.{{name}} == null{{#isNullable}} || !this.{{name}}.isPresent(){{/isNullable}}) {
       this.{{name}} = {{#isNullable}}JsonNullable.of({{{defaultValue}}}){{/isNullable}}{{^isNullable}}{{{defaultValue}}}{{/isNullable}};
     }
     {{/required}}
     this.{{name}}{{#isNullable}}.get(){{/isNullable}}.add({{name}}Item);
+    {{/openApiNullable}}
+    {{^openApiNullable}}
+    if (this.{{name}} == null) {
+      this.{{name}} = {{{defaultValue}}};
+    }
+    this.{{name}}.add({{name}}Item);
+    {{/openApiNullable}}
     return this;
   }
   {{/isListContainer}}

modules/openapi-generator/src/test/java/org/openapitools/codegen/java/jaxrs/JavaJAXRSCXFExtServerCodegenTest.java

@@ -262,6 +262,7 @@ public class JavaJAXRSCXFExtServerCodegenTest extends JavaJaxrsBaseTest {
         additionalProperties.put(AbstractJavaCodegen.SUPPORT_ASYNC, "true");
         additionalProperties.put(AbstractJavaCodegen.SUPPORT_JAVA6, "false");
         additionalProperties.put(AbstractJavaCodegen.WITH_XML, "true");
+        additionalProperties.put(AbstractJavaCodegen.OPENAPI_NULLABLE, "false");
         // Options processed by AbstractJavaJAXRSServerCodegen
         additionalProperties.put(CodegenConstants.IMPL_FOLDER, "myimpl");
         additionalProperties.put(BeanValidationFeatures.USE_BEANVALIDATION, "true");
@@ -336,6 +337,7 @@ public class JavaJAXRSCXFExtServerCodegenTest extends JavaJaxrsBaseTest {
         assertEquals(testerCodegen.isJava8Mode(), true);
         assertEquals(testerCodegen.isSupportAsync(), true);
         assertEquals(testerCodegen.isWithXml(), true);
+        assertEquals(testerCodegen.isOpenApiNullable(), false);
         // Options processed by AbstractJavaJAXRSServerCodegen
         assertEquals(testerCodegen.getImplFolder(), "myimpl");
         assertEquals(testerCodegen.isUseBeanValidation(), true);
@@ -588,6 +590,7 @@ public class JavaJAXRSCXFExtServerCodegenTest extends JavaJaxrsBaseTest {
         assertNull(additionalProperties.get(AbstractJavaCodegen.SUPPORT_ASYNC));
         assertEquals(additionalProperties.get(AbstractJavaCodegen.SUPPORT_JAVA6), Boolean.FALSE);
         assertEquals(additionalProperties.get(AbstractJavaCodegen.WITH_XML), false);
+        assertEquals(additionalProperties.get(AbstractJavaCodegen.OPENAPI_NULLABLE), true);
         // Options processed by AbstractJavaJAXRSServerCodegen
         assertNull(additionalProperties.get(CodegenConstants.IMPL_FOLDER));
         assertEquals(additionalProperties.get(BeanValidationFeatures.USE_BEANVALIDATION), Boolean.TRUE);

samples/client/petstore/java/feign-no-nullable/.gitignore

@@ -0,0 +1,21 @@
+*.class
+
+# Mobile Tools for Java (J2ME)
+.mtj.tmp/
+
+# Package Files #
+*.jar
+*.war
+*.ear
+
+# exclude jar for gradle wrapper
+!gradle/wrapper/*.jar
+
+# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
+hs_err_pid*
+
+# build files
+**/target
+target
+.gradle
+build

samples/client/petstore/java/feign-no-nullable/.openapi-generator-ignore

@@ -0,0 +1,23 @@
+# OpenAPI Generator Ignore
+# Generated by openapi-generator https://github.com/openapitools/openapi-generator
+
+# Use this file to prevent files from being overwritten by the generator.
+# The patterns follow closely to .gitignore or .dockerignore.
+
+# As an example, the C# client generator defines ApiClient.cs.
+# You can make changes and tell OpenAPI Generator to ignore just this file by uncommenting the following line:
+#ApiClient.cs
+
+# You can match any string of characters against a directory, file or extension with a single asterisk (*):
+#foo/*/qux
+# The above matches foo/bar/qux and foo/baz/qux, but not foo/bar/baz/qux
+
+# You can recursively match patterns against a directory, file or extension with a double asterisk (**):
+#foo/**/qux
+# This matches foo/bar/qux, foo/baz/qux, and foo/bar/baz/qux
+
+# You can also negate patterns with an exclamation (!).
+# For example, you can ignore all files in a docs folder with the file extension .md:
+#docs/*.md
+# Then explicitly reverse the ignore rule for a single file:
+#!docs/README.md

samples/client/petstore/java/feign-no-nullable/.openapi-generator/FILES

@@ -0,0 +1,80 @@
+.gitignore
+.travis.yml
+README.md
+api/openapi.yaml
+build.gradle
+build.sbt
+git_push.sh
+gradle.properties
+gradle/wrapper/gradle-wrapper.jar
+gradle/wrapper/gradle-wrapper.properties
+gradlew
+gradlew.bat
+pom.xml
+settings.gradle
+src/main/AndroidManifest.xml
+src/main/java/org/openapitools/client/ApiClient.java
+src/main/java/org/openapitools/client/CustomInstantDeserializer.java
+src/main/java/org/openapitools/client/EncodingUtils.java
+src/main/java/org/openapitools/client/ParamExpander.java
+src/main/java/org/openapitools/client/RFC3339DateFormat.java
+src/main/java/org/openapitools/client/ServerConfiguration.java
+src/main/java/org/openapitools/client/ServerVariable.java
+src/main/java/org/openapitools/client/StringUtil.java
+src/main/java/org/openapitools/client/api/AnotherFakeApi.java
+src/main/java/org/openapitools/client/api/FakeApi.java
+src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java
+src/main/java/org/openapitools/client/api/PetApi.java
+src/main/java/org/openapitools/client/api/StoreApi.java
+src/main/java/org/openapitools/client/api/UserApi.java
+src/main/java/org/openapitools/client/auth/ApiKeyAuth.java
+src/main/java/org/openapitools/client/auth/HttpBasicAuth.java
+src/main/java/org/openapitools/client/auth/HttpBearerAuth.java
+src/main/java/org/openapitools/client/auth/OAuth.java
+src/main/java/org/openapitools/client/auth/OAuthFlow.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesAnyType.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesArray.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesBoolean.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesClass.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesInteger.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesNumber.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesObject.java
+src/main/java/org/openapitools/client/model/AdditionalPropertiesString.java
+src/main/java/org/openapitools/client/model/Animal.java
+src/main/java/org/openapitools/client/model/ArrayOfArrayOfNumberOnly.java
+src/main/java/org/openapitools/client/model/ArrayOfNumberOnly.java
+src/main/java/org/openapitools/client/model/ArrayTest.java
+src/main/java/org/openapitools/client/model/BigCat.java
+src/main/java/org/openapitools/client/model/BigCatAllOf.java
+src/main/java/org/openapitools/client/model/Capitalization.java
+src/main/java/org/openapitools/client/model/Cat.java
+src/main/java/org/openapitools/client/model/CatAllOf.java
+src/main/java/org/openapitools/client/model/Category.java
+src/main/java/org/openapitools/client/model/ClassModel.java
+src/main/java/org/openapitools/client/model/Client.java
+src/main/java/org/openapitools/client/model/Dog.java
+src/main/java/org/openapitools/client/model/DogAllOf.java
+src/main/java/org/openapitools/client/model/EnumArrays.java
+src/main/java/org/openapitools/client/model/EnumClass.java
+src/main/java/org/openapitools/client/model/EnumTest.java
+src/main/java/org/openapitools/client/model/FileSchemaTestClass.java
+src/main/java/org/openapitools/client/model/FormatTest.java
+src/main/java/org/openapitools/client/model/HasOnlyReadOnly.java
+src/main/java/org/openapitools/client/model/MapTest.java
+src/main/java/org/openapitools/client/model/MixedPropertiesAndAdditionalPropertiesClass.java
+src/main/java/org/openapitools/client/model/Model200Response.java
+src/main/java/org/openapitools/client/model/ModelApiResponse.java
+src/main/java/org/openapitools/client/model/ModelReturn.java
+src/main/java/org/openapitools/client/model/Name.java
+src/main/java/org/openapitools/client/model/NumberOnly.java
+src/main/java/org/openapitools/client/model/Order.java
+src/main/java/org/openapitools/client/model/OuterComposite.java
+src/main/java/org/openapitools/client/model/OuterEnum.java
+src/main/java/org/openapitools/client/model/Pet.java
+src/main/java/org/openapitools/client/model/ReadOnlyFirst.java
+src/main/java/org/openapitools/client/model/SpecialModelName.java
+src/main/java/org/openapitools/client/model/Tag.java
+src/main/java/org/openapitools/client/model/TypeHolderDefault.java
+src/main/java/org/openapitools/client/model/TypeHolderExample.java
+src/main/java/org/openapitools/client/model/User.java
+src/main/java/org/openapitools/client/model/XmlItem.java

samples/client/petstore/java/feign-no-nullable/.openapi-generator/VERSION

@@ -0,0 +1 @@
+5.0.0-SNAPSHOT

samples/client/petstore/java/feign-no-nullable/.travis.yml

@@ -0,0 +1,22 @@
+#
+# Generated by OpenAPI Generator: https://openapi-generator.tech
+#
+# Ref: https://docs.travis-ci.com/user/languages/java/
+#
+language: java
+jdk:
+  - openjdk12
+  - openjdk11
+  - openjdk10
+  - openjdk9
+  - openjdk8
+before_install:
+  # ensure gradlew has proper permission
+  - chmod a+x ./gradlew
+script:
+  # test using maven
+  #- mvn test
+  # test using gradle
+  - gradle test
+  # test using sbt 
+  # - sbt test

samples/client/petstore/java/feign-no-nullable/README.md

@@ -0,0 +1,43 @@
+# petstore-feign-no-nullable
+
+## Requirements
+
+Building the API client library requires [Maven](https://maven.apache.org/) to be installed.
+
+## Installation & Usage
+
+To install the API client library to your local Maven repository, simply execute:
+
+```shell
+mvn install
+```
+
+To deploy it to a remote Maven repository instead, configure the settings of the repository and execute:
+
+```shell
+mvn deploy
+```
+
+Refer to the [official documentation](https://maven.apache.org/plugins/maven-deploy-plugin/usage.html) for more information.
+
+After the client library is installed/deployed, you can use it in your Maven project by adding the following to your *pom.xml*:
+
+```xml
+<dependency>
+    <groupId>org.openapitools</groupId>
+    <artifactId>petstore-feign-no-nullable</artifactId>
+    <version>1.0.0</version>
+    <scope>compile</scope>
+</dependency>
+
+```
+
+## Recommendation
+
+It's recommended to create an instance of `ApiClient` per thread in a multithreaded environment to avoid any potential issues.
+
+## Author
+
+
+
+

samples/client/petstore/java/feign-no-nullable/build.gradle

@@ -0,0 +1,123 @@
+apply plugin: 'idea'
+apply plugin: 'eclipse'
+
+group = 'org.openapitools'
+version = '1.0.0'
+
+buildscript {
+    repositories {
+        maven { url "https://repo1.maven.org/maven2" }
+        jcenter()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:2.3.+'
+        classpath 'com.github.dcendents:android-maven-gradle-plugin:1.5'
+    }
+}
+
+repositories {
+    jcenter()
+}
+
+
+if(hasProperty('target') && target == 'android') {
+
+    apply plugin: 'com.android.library'
+    apply plugin: 'com.github.dcendents.android-maven'
+
+    android {
+        compileSdkVersion 25
+        buildToolsVersion '25.0.2'
+        defaultConfig {
+            minSdkVersion 14
+            targetSdkVersion 25
+        }
+        compileOptions {
+            sourceCompatibility JavaVersion.VERSION_1_7
+            targetCompatibility JavaVersion.VERSION_1_7
+        }
+
+        // Rename the aar correctly
+        libraryVariants.all { variant ->
+            variant.outputs.each { output ->
+                def outputFile = output.outputFile
+                if (outputFile != null && outputFile.name.endsWith('.aar')) {
+                    def fileName = "${project.name}-${variant.baseName}-${version}.aar"
+                    output.outputFile = new File(outputFile.parent, fileName)
+                }
+            }
+        }
+
+        dependencies {
+            provided 'javax.annotation:jsr250-api:1.0'
+        }
+    }
+
+    afterEvaluate {
+        android.libraryVariants.all { variant ->
+            def task = project.tasks.create "jar${variant.name.capitalize()}", Jar
+            task.description = "Create jar artifact for ${variant.name}"
+            task.dependsOn variant.javaCompile
+            task.from variant.javaCompile.destinationDir
+            task.destinationDir = project.file("${project.buildDir}/outputs/jar")
+            task.archiveName = "${project.name}-${variant.baseName}-${version}.jar"
+            artifacts.add('archives', task);
+        }
+    }
+
+    task sourcesJar(type: Jar) {
+        from android.sourceSets.main.java.srcDirs
+        classifier = 'sources'
+    }
+
+    artifacts {
+        archives sourcesJar
+    }
+
+} else {
+
+    apply plugin: 'java'
+    apply plugin: 'maven'
+
+    sourceCompatibility = JavaVersion.VERSION_1_7
+    targetCompatibility = JavaVersion.VERSION_1_7
+
+    install {
+        repositories.mavenInstaller {
+            pom.artifactId = 'petstore-feign-no-nullable'
+        }
+    }
+
+    task execute(type:JavaExec) {
+       main = System.getProperty('mainClass')
+       classpath = sourceSets.main.runtimeClasspath
+    }
+}
+
+ext {
+    swagger_annotations_version = "1.5.24"
+    jackson_version = "2.10.3"
+    jackson_databind_version = "2.10.3"
+    jackson_threetenbp_version = "2.9.10"
+    feign_version = "10.11"
+    feign_form_version = "3.8.0"
+    junit_version = "4.13"
+    oltu_version = "1.0.1"
+}
+
+dependencies {
+    compile "io.swagger:swagger-annotations:$swagger_annotations_version"
+    compile "com.google.code.findbugs:jsr305:3.0.2"
+    compile "io.github.openfeign:feign-core:$feign_version"
+    compile "io.github.openfeign:feign-jackson:$feign_version"
+    compile "io.github.openfeign:feign-slf4j:$feign_version"
+    compile "io.github.openfeign.form:feign-form:$feign_form_version"
+    compile "com.fasterxml.jackson.core:jackson-core:$jackson_version"
+    compile "com.fasterxml.jackson.core:jackson-annotations:$jackson_version"
+    compile "com.fasterxml.jackson.core:jackson-databind:$jackson_databind_version"
+    compile "com.github.joschi.jackson:jackson-datatype-threetenbp:$jackson_threetenbp_version"
+    compile "org.apache.oltu.oauth2:org.apache.oltu.oauth2.client:$oltu_version"
+    compile "com.brsanthu:migbase64:2.2"
+    compile 'javax.annotation:javax.annotation-api:1.3.2'
+    testCompile "junit:junit:$junit_version"
+}

samples/client/petstore/java/feign-no-nullable/build.sbt

@@ -0,0 +1,28 @@
+lazy val root = (project in file(".")).
+  settings(
+    organization := "org.openapitools",
+    name := "petstore-feign-no-nullable",
+    version := "1.0.0",
+    scalaVersion := "2.11.4",
+    scalacOptions ++= Seq("-feature"),
+    javacOptions in compile ++= Seq("-Xlint:deprecation"),
+    publishArtifact in (Compile, packageDoc) := false,
+    resolvers += Resolver.mavenLocal,
+    libraryDependencies ++= Seq(
+      "io.swagger" % "swagger-annotations" % "1.5.24" % "compile",
+      "io.github.openfeign" % "feign-core" % "10.11" % "compile",
+      "io.github.openfeign" % "feign-jackson" % "10.11" % "compile",
+      "io.github.openfeign" % "feign-slf4j" % "10.11" % "compile",
+      "io.github.openfeign.form" % "feign-form" % "3.8.0" % "compile",
+      "com.fasterxml.jackson.core" % "jackson-core" % "2.10.3" % "compile",
+      "com.fasterxml.jackson.core" % "jackson-annotations" % "2.10.3" % "compile",
+      "com.fasterxml.jackson.core" % "jackson-databind" % "2.10.3" % "compile",
+      "com.fasterxml.jackson.datatype" % "jackson-datatype-joda" % "2.9.10" % "compile",
+      "com.github.joschi.jackson" % "jackson-datatype-threetenbp" % "2.9.10" % "compile",
+      "org.apache.oltu.oauth2" % "org.apache.oltu.oauth2.client" % "1.0.1" % "compile",
+      "com.brsanthu" % "migbase64" % "2.2" % "compile",
+      "javax.annotation" % "javax.annotation-api" % "1.3.2" % "compile",
+      "junit" % "junit" % "4.13" % "test",
+      "com.novocode" % "junit-interface" % "0.10" % "test"
+    )
+  )

samples/client/petstore/java/feign-no-nullable/git_push.sh

@@ -0,0 +1,58 @@
+#!/bin/sh
+# ref: https://help.github.com/articles/adding-an-existing-project-to-github-using-the-command-line/
+#
+# Usage example: /bin/sh ./git_push.sh wing328 openapi-pestore-perl "minor update" "gitlab.com"
+
+git_user_id=$1
+git_repo_id=$2
+release_note=$3
+git_host=$4
+
+if [ "$git_host" = "" ]; then
+    git_host="github.com"
+    echo "[INFO] No command line input provided. Set \$git_host to $git_host"
+fi
+
+if [ "$git_user_id" = "" ]; then
+    git_user_id="GIT_USER_ID"
+    echo "[INFO] No command line input provided. Set \$git_user_id to $git_user_id"
+fi
+
+if [ "$git_repo_id" = "" ]; then
+    git_repo_id="GIT_REPO_ID"
+    echo "[INFO] No command line input provided. Set \$git_repo_id to $git_repo_id"
+fi
+
+if [ "$release_note" = "" ]; then
+    release_note="Minor update"
+    echo "[INFO] No command line input provided. Set \$release_note to $release_note"
+fi
+
+# Initialize the local directory as a Git repository
+git init
+
+# Adds the files in the local repository and stages them for commit.
+git add .
+
+# Commits the tracked changes and prepares them to be pushed to a remote repository.
+git commit -m "$release_note"
+
+# Sets the new remote
+git_remote=`git remote`
+if [ "$git_remote" = "" ]; then # git remote not defined
+
+    if [ "$GIT_TOKEN" = "" ]; then
+        echo "[INFO] \$GIT_TOKEN (environment variable) is not set. Using the git credential in your environment."
+        git remote add origin https://${git_host}/${git_user_id}/${git_repo_id}.git
+    else
+        git remote add origin https://${git_user_id}:${GIT_TOKEN}@${git_host}/${git_user_id}/${git_repo_id}.git
+    fi
+
+fi
+
+git pull origin master
+
+# Pushes (Forces) the changes in the local repository up to the remote repository
+echo "Git pushing to https://${git_host}/${git_user_id}/${git_repo_id}.git"
+git push origin master 2>&1 | grep -v 'To https'
+

samples/client/petstore/java/feign-no-nullable/gradle.properties

@@ -0,0 +1,2 @@
+# Uncomment to build for Android
+#target = android

samples/client/petstore/java/feign-no-nullable/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.0.1-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

samples/client/petstore/java/feign-no-nullable/gradlew

@@ -0,0 +1,183 @@
+#!/usr/bin/env sh
+
+#
+# Copyright 2015 the original author or authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if [ "$cygwin" = "true" -o "$msys" = "true" ] ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=`expr $i + 1`
+    done
+    case $i in
+        0) set -- ;;
+        1) set -- "$args0" ;;
+        2) set -- "$args0" "$args1" ;;
+        3) set -- "$args0" "$args1" "$args2" ;;
+        4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=`save "$@"`
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+exec "$JAVACMD" "$@"

samples/client/petstore/java/feign-no-nullable/gradlew.bat

@@ -0,0 +1,100 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

samples/client/petstore/java/feign-no-nullable/pom.xml

@@ -0,0 +1,313 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>org.openapitools</groupId>
+    <artifactId>petstore-feign-no-nullable</artifactId>
+    <packaging>jar</packaging>
+    <name>petstore-feign-no-nullable</name>
+    <version>1.0.0</version>
+    <url>https://github.com/openapitools/openapi-generator</url>
+    <description>OpenAPI Java</description>
+    <scm>
+        <connection>scm:git:git@github.com:openapitools/openapi-generator.git</connection>
+        <developerConnection>scm:git:git@github.com:openapitools/openapi-generator.git</developerConnection>
+        <url>https://github.com/openapitools/openapi-generator</url>
+    </scm>
+
+    <licenses>
+        <license>
+            <name>Unlicense</name>
+            <url>https://www.apache.org/licenses/LICENSE-2.0.html</url>
+            <distribution>repo</distribution>
+        </license>
+    </licenses>
+
+    <developers>
+        <developer>
+            <name>OpenAPI-Generator Contributors</name>
+            <email>team@openapitools.org</email>
+            <organization>OpenAPITools.org</organization>
+            <organizationUrl>http://openapitools.org</organizationUrl>
+        </developer>
+    </developers>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-enforcer-plugin</artifactId>
+                <version>3.0.0-M1</version>
+                <executions>
+                    <execution>
+                        <id>enforce-maven</id>
+                        <goals>
+                            <goal>enforce</goal>
+                        </goals>
+                        <configuration>
+                            <rules>
+                                <requireMavenVersion>
+                                    <version>2.2.0</version>
+                                </requireMavenVersion>
+                            </rules>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>3.0.0-M4</version>
+                <configuration>
+                    <systemProperties>
+                        <property>
+                            <name>loggerPath</name>
+                            <value>conf/log4j.properties</value>
+                        </property>
+                    </systemProperties>
+                    <argLine>-Xms512m -Xmx1500m</argLine>
+                    <parallel>methods</parallel>
+                    <threadCount>10</threadCount>
+                </configuration>
+            </plugin>
+            <plugin>
+                <artifactId>maven-dependency-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>copy-dependencies</goal>
+                        </goals>
+                        <configuration>
+                            <outputDirectory>${project.build.directory}/lib</outputDirectory>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <!-- attach test jar -->
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>2.2</version>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>jar</goal>
+                            <goal>test-jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                </configuration>
+            </plugin>
+
+            <plugin>
+                <groupId>org.codehaus.mojo</groupId>
+                <artifactId>build-helper-maven-plugin</artifactId>
+                <version>1.10</version>
+                <executions>
+                    <execution>
+                        <id>add_sources</id>
+                        <phase>generate-sources</phase>
+                        <goals>
+                            <goal>add-source</goal>
+                        </goals>
+                        <configuration>
+                            <sources>
+                                <source>src/main/java</source>
+                            </sources>
+                        </configuration>
+                    </execution>
+                    <execution>
+                        <id>add_test_sources</id>
+                        <phase>generate-test-sources</phase>
+                        <goals>
+                            <goal>add-test-source</goal>
+                        </goals>
+                        <configuration>
+                            <sources>
+                                <source>src/test/java</source>
+                            </sources>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+                <configuration>
+                        <source>1.8</source>
+                        <target>1.8</target>
+                    <fork>true</fork>
+                    <meminitial>128m</meminitial>
+                    <maxmem>512m</maxmem>
+                    <compilerArgs>
+                        <arg>-Xlint:all</arg>
+                        <arg>-J-Xss4m</arg><!-- Compiling the generated JSON.java file may require larger stack size. -->
+                    </compilerArgs>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <version>3.1.1</version>
+                <configuration>
+                    <doclint>none</doclint>
+                        <source>1.7</source>
+                </configuration>
+                <executions>
+                    <execution>
+                        <id>attach-javadocs</id>
+                        <goals>
+                            <goal>jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-source-plugin</artifactId>
+                <version>2.2.1</version>
+                <executions>
+                    <execution>
+                        <id>attach-sources</id>
+                        <goals>
+                            <goal>jar-no-fork</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+
+    <profiles>
+        <profile>
+            <id>sign-artifacts</id>
+            <build>
+                <plugins>
+                    <plugin>
+                        <groupId>org.apache.maven.plugins</groupId>
+                        <artifactId>maven-gpg-plugin</artifactId>
+                        <version>1.5</version>
+                        <executions>
+                            <execution>
+                                <id>sign-artifacts</id>
+                                <phase>verify</phase>
+                                <goals>
+                                    <goal>sign</goal>
+                                </goals>
+                            </execution>
+                        </executions>
+                    </plugin>
+                </plugins>
+            </build>
+        </profile>
+    </profiles>
+
+    <dependencies>
+        <dependency>
+            <groupId>io.swagger</groupId>
+            <artifactId>swagger-annotations</artifactId>
+            <version>${swagger-annotations-version}</version>
+        </dependency>
+
+        <!-- @Nullable annotation -->
+        <dependency>
+            <groupId>com.google.code.findbugs</groupId>
+            <artifactId>jsr305</artifactId>
+            <version>3.0.2</version>
+        </dependency>
+        
+        <!-- HTTP client: Netflix Feign -->
+        <dependency>
+            <groupId>io.github.openfeign</groupId>
+            <artifactId>feign-core</artifactId>
+            <version>${feign-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.github.openfeign</groupId>
+            <artifactId>feign-jackson</artifactId>
+            <version>${feign-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.github.openfeign</groupId>
+            <artifactId>feign-slf4j</artifactId>
+            <version>${feign-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.github.openfeign.form</groupId>
+            <artifactId>feign-form</artifactId>
+            <version>${feign-form-version}</version>
+        </dependency>
+
+        <!-- JSON processing: jackson -->
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>${jackson-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-annotations</artifactId>
+            <version>${jackson-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-databind</artifactId>
+            <version>${jackson-databind-version}</version>
+        </dependency>
+            <dependency>
+                <groupId>com.github.joschi.jackson</groupId>
+                <artifactId>jackson-datatype-threetenbp</artifactId>
+                <version>${jackson-threetenbp-version}</version>
+            </dependency>
+        <dependency>
+            <groupId>org.apache.oltu.oauth2</groupId>
+            <artifactId>org.apache.oltu.oauth2.client</artifactId>
+            <version>${oltu-version}</version>
+        </dependency>
+        <dependency>
+            <groupId>javax.annotation</groupId>
+            <artifactId>javax.annotation-api</artifactId>
+            <version>${javax-annotation-version}</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- test dependencies -->
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit-version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.squareup.okhttp3</groupId>
+            <artifactId>mockwebserver</artifactId>
+            <version>3.6.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>1.7.1</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <java.version>1.7</java.version>
+        <maven.compiler.source>${java.version}</maven.compiler.source>
+        <maven.compiler.target>${java.version}</maven.compiler.target>
+        <swagger-annotations-version>1.5.24</swagger-annotations-version>
+        <feign-version>10.11</feign-version>
+        <feign-form-version>3.8.0</feign-form-version>
+        <jackson-version>2.10.3</jackson-version>
+        <jackson-databind-version>2.10.3</jackson-databind-version>
+        <jackson-threetenbp-version>2.9.10</jackson-threetenbp-version>
+        <javax-annotation-version>1.3.2</javax-annotation-version>
+        <junit-version>4.13</junit-version>
+        <maven-plugin-version>1.0.0</maven-plugin-version>
+        <oltu-version>1.0.1</oltu-version>
+    </properties>
+</project>

samples/client/petstore/java/feign-no-nullable/settings.gradle

@@ -0,0 +1 @@
+rootProject.name = "petstore-feign-no-nullable"

samples/client/petstore/java/feign-no-nullable/src/main/AndroidManifest.xml

@@ -0,0 +1,3 @@
+<manifest package="org.openapitools.client" xmlns:android="http://schemas.android.com/apk/res/android">
+    <application />
+</manifest>

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ApiClient.java

@@ -0,0 +1,352 @@
+package org.openapitools.client;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+import org.apache.oltu.oauth2.client.request.OAuthClientRequest.AuthenticationRequestBuilder;
+import org.apache.oltu.oauth2.client.request.OAuthClientRequest.TokenRequestBuilder;
+
+import org.threeten.bp.*;
+
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.datatype.threetenbp.ThreeTenModule;
+
+import feign.Feign;
+import feign.RequestInterceptor;
+import feign.form.FormEncoder;
+import feign.jackson.JacksonDecoder;
+import feign.jackson.JacksonEncoder;
+import feign.slf4j.Slf4jLogger;
+import org.openapitools.client.auth.*;
+import org.openapitools.client.auth.OAuth.AccessTokenListener;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class ApiClient {
+  public interface Api {}
+
+  protected ObjectMapper objectMapper;
+  private String basePath = "http://petstore.swagger.io:80/v2";
+  private Map<String, RequestInterceptor> apiAuthorizations;
+  private Feign.Builder feignBuilder;
+
+  public ApiClient() {
+    objectMapper = createObjectMapper();
+    apiAuthorizations = new LinkedHashMap<String, RequestInterceptor>();
+    feignBuilder = Feign.builder()
+                .encoder(new FormEncoder(new JacksonEncoder(objectMapper)))
+                .decoder(new JacksonDecoder(objectMapper))
+                .logger(new Slf4jLogger());
+  }
+
+  public ApiClient(String[] authNames) {
+    this();
+    for(String authName : authNames) {
+      RequestInterceptor auth;
+      if ("api_key".equals(authName)) {
+        auth = new ApiKeyAuth("header", "api_key");
+      } else if ("api_key_query".equals(authName)) {
+        auth = new ApiKeyAuth("query", "api_key_query");
+      } else if ("http_basic_test".equals(authName)) {
+        auth = new HttpBasicAuth();
+      } else if ("petstore_auth".equals(authName)) {
+        auth = new OAuth(OAuthFlow.implicit, "http://petstore.swagger.io/api/oauth/dialog", "", "write:pets, read:pets");
+      } else {
+        throw new RuntimeException("auth name \"" + authName + "\" not found in available auth names");
+      }
+      addAuthorization(authName, auth);
+    }
+  }
+
+  /**
+   * Basic constructor for single auth name
+   * @param authName
+   */
+  public ApiClient(String authName) {
+    this(new String[]{authName});
+  }
+
+  /**
+   * Helper constructor for single api key
+   * @param authName
+   * @param apiKey
+   */
+  public ApiClient(String authName, String apiKey) {
+    this(authName);
+    this.setApiKey(apiKey);
+  }
+
+  /**
+   * Helper constructor for single basic auth or password oauth2
+   * @param authName
+   * @param username
+   * @param password
+   */
+  public ApiClient(String authName, String username, String password) {
+    this(authName);
+    this.setCredentials(username,  password);
+  }
+
+  /**
+   * Helper constructor for single password oauth2
+   * @param authName
+   * @param clientId
+   * @param secret
+   * @param username
+   * @param password
+   */
+  public ApiClient(String authName, String clientId, String secret, String username, String password) {
+    this(authName);
+    this.getTokenEndPoint()
+           .setClientId(clientId)
+           .setClientSecret(secret)
+           .setUsername(username)
+           .setPassword(password);
+  }
+
+  public String getBasePath() {
+    return basePath;
+  }
+
+  public ApiClient setBasePath(String basePath) {
+    this.basePath = basePath;
+    return this;
+  }
+
+  public Map<String, RequestInterceptor> getApiAuthorizations() {
+    return apiAuthorizations;
+  }
+
+  public void setApiAuthorizations(Map<String, RequestInterceptor> apiAuthorizations) {
+    this.apiAuthorizations = apiAuthorizations;
+  }
+
+  public Feign.Builder getFeignBuilder() {
+    return feignBuilder;
+  }
+
+  public ApiClient setFeignBuilder(Feign.Builder feignBuilder) {
+    this.feignBuilder = feignBuilder;
+    return this;
+  }
+
+  private ObjectMapper createObjectMapper() {
+    ObjectMapper objectMapper = new ObjectMapper();
+    objectMapper.enable(SerializationFeature.WRITE_ENUMS_USING_TO_STRING);
+    objectMapper.enable(DeserializationFeature.READ_ENUMS_USING_TO_STRING);
+    objectMapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
+    objectMapper.disable(DeserializationFeature.FAIL_ON_INVALID_SUBTYPE);
+    objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
+    objectMapper.setDateFormat(new RFC3339DateFormat());
+    ThreeTenModule module = new ThreeTenModule();
+    module.addDeserializer(Instant.class, CustomInstantDeserializer.INSTANT);
+    module.addDeserializer(OffsetDateTime.class, CustomInstantDeserializer.OFFSET_DATE_TIME);
+    module.addDeserializer(ZonedDateTime.class, CustomInstantDeserializer.ZONED_DATE_TIME);
+    objectMapper.registerModule(module);
+    return objectMapper;
+  }
+
+  public ObjectMapper getObjectMapper(){
+    return objectMapper;
+  }
+
+  /**
+   * Creates a feign client for given API interface.
+   *
+   * Usage:
+   *    ApiClient apiClient = new ApiClient();
+   *    apiClient.setBasePath("http://localhost:8080");
+   *    XYZApi api = apiClient.buildClient(XYZApi.class);
+   *    XYZResponse response = api.someMethod(...);
+   * @param <T> Type
+   * @param clientClass Client class
+   * @return The Client
+   */
+  public <T extends Api> T buildClient(Class<T> clientClass) {
+    return feignBuilder.target(clientClass, basePath);
+  }
+
+  /**
+   * Select the Accept header's value from the given accepts array:
+   *   if JSON exists in the given array, use it;
+   *   otherwise use all of them (joining into a string)
+   *
+   * @param accepts The accepts array to select from
+   * @return The Accept header to use. If the given array is empty,
+   *   null will be returned (not to set the Accept header explicitly).
+   */
+  public String selectHeaderAccept(String[] accepts) {
+    if (accepts.length == 0) return null;
+    if (StringUtil.containsIgnoreCase(accepts, "application/json")) return "application/json";
+    return StringUtil.join(accepts, ",");
+  }
+
+  /**
+   * Select the Content-Type header's value from the given array:
+   *   if JSON exists in the given array, use it;
+   *   otherwise use the first one of the array.
+   *
+   * @param contentTypes The Content-Type array to select from
+   * @return The Content-Type header to use. If the given array is empty,
+   *   JSON will be used.
+   */
+  public String selectHeaderContentType(String[] contentTypes) {
+    if (contentTypes.length == 0) return "application/json";
+    if (StringUtil.containsIgnoreCase(contentTypes, "application/json")) return "application/json";
+    return contentTypes[0];
+  }
+
+
+  /**
+   * Helper method to configure the bearer token.
+   * @param bearerToken the bearer token.
+   */
+  public void setBearerToken(String bearerToken) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof HttpBearerAuth) {
+        ((HttpBearerAuth) apiAuthorization).setBearerToken(bearerToken);
+        return;
+      }
+    }
+    throw new RuntimeException("No Bearer authentication configured!");
+  }
+
+  /**
+   * Helper method to configure the first api key found
+   * @param apiKey API key
+   */
+  public void setApiKey(String apiKey) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof ApiKeyAuth) {
+        ApiKeyAuth keyAuth = (ApiKeyAuth) apiAuthorization;
+        keyAuth.setApiKey(apiKey);
+        return ;
+      }
+    }
+    throw new RuntimeException("No API key authentication configured!");
+  }
+
+  /**
+   * Helper method to configure the username/password for basic auth or password OAuth
+   * @param username Username
+   * @param password Password
+   */
+  public void setCredentials(String username, String password) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof HttpBasicAuth) {
+        HttpBasicAuth basicAuth = (HttpBasicAuth) apiAuthorization;
+        basicAuth.setCredentials(username, password);
+        return;
+      }
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        oauth.getTokenRequestBuilder().setUsername(username).setPassword(password);
+        return;
+      }
+    }
+    throw new RuntimeException("No Basic authentication or OAuth configured!");
+  }
+
+  /**
+   * Helper method to configure the token endpoint of the first oauth found in the apiAuthorizations (there should be only one)
+   * @return Token request builder
+   */
+  public TokenRequestBuilder getTokenEndPoint() {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        return oauth.getTokenRequestBuilder();
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Helper method to configure authorization endpoint of the first oauth found in the apiAuthorizations (there should be only one)
+   * @return Authentication request builder
+   */
+  public AuthenticationRequestBuilder getAuthorizationEndPoint() {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        return oauth.getAuthenticationRequestBuilder();
+      }
+    }
+    return null;
+  }
+
+  /**
+   * Helper method to pre-set the oauth access token of the first oauth found in the apiAuthorizations (there should be only one)
+   * @param accessToken Access Token
+   * @param expiresIn Validity period in seconds
+   */
+  public void setAccessToken(String accessToken, Long expiresIn) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        oauth.setAccessToken(accessToken, expiresIn);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Helper method to configure the oauth accessCode/implicit flow parameters
+   * @param clientId Client ID
+   * @param clientSecret Client secret
+   * @param redirectURI Redirect URI
+   */
+  public void configureAuthorizationFlow(String clientId, String clientSecret, String redirectURI) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        oauth.getTokenRequestBuilder()
+                .setClientId(clientId)
+                .setClientSecret(clientSecret)
+                .setRedirectURI(redirectURI);
+        oauth.getAuthenticationRequestBuilder()
+                .setClientId(clientId)
+                .setRedirectURI(redirectURI);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Configures a listener which is notified when a new access token is received.
+   * @param accessTokenListener Acesss token listener
+   */
+  public void registerAccessTokenListener(AccessTokenListener accessTokenListener) {
+    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
+      if (apiAuthorization instanceof OAuth) {
+        OAuth oauth = (OAuth) apiAuthorization;
+        oauth.registerAccessTokenListener(accessTokenListener);
+        return;
+      }
+    }
+  }
+
+  /**
+   * Gets request interceptor based on authentication name
+   * @param authName Authentiation name
+   * @return Request Interceptor
+   */
+  public RequestInterceptor getAuthorization(String authName) {
+    return apiAuthorizations.get(authName);
+  }
+
+  /**
+   * Adds an authorization to be used by the client
+   * @param authName Authentication name
+   * @param authorization Request interceptor
+   */
+  public void addAuthorization(String authName, RequestInterceptor authorization) {
+    if (apiAuthorizations.containsKey(authName)) {
+      throw new RuntimeException("auth name \"" + authName + "\" already in api authorizations");
+    }
+    apiAuthorizations.put(authName, authorization);
+    feignBuilder.requestInterceptor(authorization);
+  }
+
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/CustomInstantDeserializer.java

@@ -0,0 +1,232 @@
+package org.openapitools.client;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonTokenId;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import com.fasterxml.jackson.databind.JsonDeserializer;
+import com.fasterxml.jackson.datatype.threetenbp.DecimalUtils;
+import com.fasterxml.jackson.datatype.threetenbp.deser.ThreeTenDateTimeDeserializerBase;
+import com.fasterxml.jackson.datatype.threetenbp.function.BiFunction;
+import com.fasterxml.jackson.datatype.threetenbp.function.Function;
+import org.threeten.bp.DateTimeException;
+import org.threeten.bp.DateTimeUtils;
+import org.threeten.bp.Instant;
+import org.threeten.bp.OffsetDateTime;
+import org.threeten.bp.ZoneId;
+import org.threeten.bp.ZonedDateTime;
+import org.threeten.bp.format.DateTimeFormatter;
+import org.threeten.bp.temporal.Temporal;
+import org.threeten.bp.temporal.TemporalAccessor;
+
+import java.io.IOException;
+import java.math.BigDecimal;
+
+/**
+ * Deserializer for ThreeTen temporal {@link Instant}s, {@link OffsetDateTime}, and {@link ZonedDateTime}s.
+ * Adapted from the jackson threetenbp InstantDeserializer to add support for deserializing rfc822 format.
+ *
+ * @author Nick Williams
+ */
+public class CustomInstantDeserializer<T extends Temporal>
+    extends ThreeTenDateTimeDeserializerBase<T> {
+  private static final long serialVersionUID = 1L;
+
+  public static final CustomInstantDeserializer<Instant> INSTANT = new CustomInstantDeserializer<Instant>(
+      Instant.class, DateTimeFormatter.ISO_INSTANT,
+      new Function<TemporalAccessor, Instant>() {
+        @Override
+        public Instant apply(TemporalAccessor temporalAccessor) {
+          return Instant.from(temporalAccessor);
+        }
+      },
+      new Function<FromIntegerArguments, Instant>() {
+        @Override
+        public Instant apply(FromIntegerArguments a) {
+          return Instant.ofEpochMilli(a.value);
+        }
+      },
+      new Function<FromDecimalArguments, Instant>() {
+        @Override
+        public Instant apply(FromDecimalArguments a) {
+          return Instant.ofEpochSecond(a.integer, a.fraction);
+        }
+      },
+      null
+  );
+
+  public static final CustomInstantDeserializer<OffsetDateTime> OFFSET_DATE_TIME = new CustomInstantDeserializer<OffsetDateTime>(
+      OffsetDateTime.class, DateTimeFormatter.ISO_OFFSET_DATE_TIME,
+      new Function<TemporalAccessor, OffsetDateTime>() {
+        @Override
+        public OffsetDateTime apply(TemporalAccessor temporalAccessor) {
+          return OffsetDateTime.from(temporalAccessor);
+        }
+      },
+      new Function<FromIntegerArguments, OffsetDateTime>() {
+        @Override
+        public OffsetDateTime apply(FromIntegerArguments a) {
+          return OffsetDateTime.ofInstant(Instant.ofEpochMilli(a.value), a.zoneId);
+        }
+      },
+      new Function<FromDecimalArguments, OffsetDateTime>() {
+        @Override
+        public OffsetDateTime apply(FromDecimalArguments a) {
+          return OffsetDateTime.ofInstant(Instant.ofEpochSecond(a.integer, a.fraction), a.zoneId);
+        }
+      },
+      new BiFunction<OffsetDateTime, ZoneId, OffsetDateTime>() {
+        @Override
+        public OffsetDateTime apply(OffsetDateTime d, ZoneId z) {
+          return d.withOffsetSameInstant(z.getRules().getOffset(d.toLocalDateTime()));
+        }
+      }
+  );
+
+  public static final CustomInstantDeserializer<ZonedDateTime> ZONED_DATE_TIME = new CustomInstantDeserializer<ZonedDateTime>(
+      ZonedDateTime.class, DateTimeFormatter.ISO_ZONED_DATE_TIME,
+      new Function<TemporalAccessor, ZonedDateTime>() {
+        @Override
+        public ZonedDateTime apply(TemporalAccessor temporalAccessor) {
+          return ZonedDateTime.from(temporalAccessor);
+        }
+      },
+      new Function<FromIntegerArguments, ZonedDateTime>() {
+        @Override
+        public ZonedDateTime apply(FromIntegerArguments a) {
+          return ZonedDateTime.ofInstant(Instant.ofEpochMilli(a.value), a.zoneId);
+        }
+      },
+      new Function<FromDecimalArguments, ZonedDateTime>() {
+        @Override
+        public ZonedDateTime apply(FromDecimalArguments a) {
+          return ZonedDateTime.ofInstant(Instant.ofEpochSecond(a.integer, a.fraction), a.zoneId);
+        }
+      },
+      new BiFunction<ZonedDateTime, ZoneId, ZonedDateTime>() {
+        @Override
+        public ZonedDateTime apply(ZonedDateTime zonedDateTime, ZoneId zoneId) {
+          return zonedDateTime.withZoneSameInstant(zoneId);
+        }
+      }
+  );
+
+  protected final Function<FromIntegerArguments, T> fromMilliseconds;
+
+  protected final Function<FromDecimalArguments, T> fromNanoseconds;
+
+  protected final Function<TemporalAccessor, T> parsedToValue;
+
+  protected final BiFunction<T, ZoneId, T> adjust;
+
+  protected CustomInstantDeserializer(Class<T> supportedType,
+                    DateTimeFormatter parser,
+                    Function<TemporalAccessor, T> parsedToValue,
+                    Function<FromIntegerArguments, T> fromMilliseconds,
+                    Function<FromDecimalArguments, T> fromNanoseconds,
+                    BiFunction<T, ZoneId, T> adjust) {
+    super(supportedType, parser);
+    this.parsedToValue = parsedToValue;
+    this.fromMilliseconds = fromMilliseconds;
+    this.fromNanoseconds = fromNanoseconds;
+    this.adjust = adjust == null ? new BiFunction<T, ZoneId, T>() {
+      @Override
+      public T apply(T t, ZoneId zoneId) {
+        return t;
+      }
+    } : adjust;
+  }
+
+  @SuppressWarnings("unchecked")
+  protected CustomInstantDeserializer(CustomInstantDeserializer<T> base, DateTimeFormatter f) {
+    super((Class<T>) base.handledType(), f);
+    parsedToValue = base.parsedToValue;
+    fromMilliseconds = base.fromMilliseconds;
+    fromNanoseconds = base.fromNanoseconds;
+    adjust = base.adjust;
+  }
+
+  @Override
+  protected JsonDeserializer<T> withDateFormat(DateTimeFormatter dtf) {
+    if (dtf == _formatter) {
+      return this;
+    }
+    return new CustomInstantDeserializer<T>(this, dtf);
+  }
+
+  @Override
+  public T deserialize(JsonParser parser, DeserializationContext context) throws IOException {
+    //NOTE: Timestamps contain no timezone info, and are always in configured TZ. Only
+    //string values have to be adjusted to the configured TZ.
+    switch (parser.getCurrentTokenId()) {
+      case JsonTokenId.ID_NUMBER_FLOAT: {
+        BigDecimal value = parser.getDecimalValue();
+        long seconds = value.longValue();
+        int nanoseconds = DecimalUtils.extractNanosecondDecimal(value, seconds);
+        return fromNanoseconds.apply(new FromDecimalArguments(
+            seconds, nanoseconds, getZone(context)));
+      }
+
+      case JsonTokenId.ID_NUMBER_INT: {
+        long timestamp = parser.getLongValue();
+        if (context.isEnabled(DeserializationFeature.READ_DATE_TIMESTAMPS_AS_NANOSECONDS)) {
+          return this.fromNanoseconds.apply(new FromDecimalArguments(
+              timestamp, 0, this.getZone(context)
+          ));
+        }
+        return this.fromMilliseconds.apply(new FromIntegerArguments(
+            timestamp, this.getZone(context)
+        ));
+      }
+
+      case JsonTokenId.ID_STRING: {
+        String string = parser.getText().trim();
+        if (string.length() == 0) {
+          return null;
+        }
+        if (string.endsWith("+0000")) {
+          string = string.substring(0, string.length() - 5) + "Z";
+        }
+        T value;
+        try {
+          TemporalAccessor acc = _formatter.parse(string);
+          value = parsedToValue.apply(acc);
+          if (context.isEnabled(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE)) {
+            return adjust.apply(value, this.getZone(context));
+          }
+        } catch (DateTimeException e) {
+          throw _peelDTE(e);
+        }
+        return value;
+      }
+    }
+    throw context.mappingException("Expected type float, integer, or string.");
+  }
+
+  private ZoneId getZone(DeserializationContext context) {
+    // Instants are always in UTC, so don't waste compute cycles
+    return (_valueClass == Instant.class) ? null : DateTimeUtils.toZoneId(context.getTimeZone());
+  }
+
+  private static class FromIntegerArguments {
+    public final long value;
+    public final ZoneId zoneId;
+
+    private FromIntegerArguments(long value, ZoneId zoneId) {
+      this.value = value;
+      this.zoneId = zoneId;
+    }
+  }
+
+  private static class FromDecimalArguments {
+    public final long integer;
+    public final int fraction;
+    public final ZoneId zoneId;
+
+    private FromDecimalArguments(long integer, int fraction, ZoneId zoneId) {
+      this.integer = integer;
+      this.fraction = fraction;
+      this.zoneId = zoneId;
+    }
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/EncodingUtils.java

@@ -0,0 +1,86 @@
+package org.openapitools.client;
+
+import java.io.UnsupportedEncodingException;
+import java.net.URLEncoder;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+/**
+* Utilities to support Swagger encoding formats in Feign.
+*/
+public final class EncodingUtils {
+
+  /**
+   * Private constructor. Do not construct this class.
+   */
+  private EncodingUtils() {}
+
+  /**
+   * <p>Encodes a collection of query parameters according to the Swagger
+   * collection format.</p>
+   *
+   * <p>Of the various collection formats defined by Swagger ("csv", "tsv",
+   * etc), Feign only natively supports "multi". This utility generates the
+   * other format types so it will be properly processed by Feign.</p>
+   *
+   * <p>Note, as part of reformatting, it URL encodes the parameters as
+   * well.</p>
+   * @param parameters The collection object to be formatted. This object will
+   *                   not be changed.
+   * @param collectionFormat The Swagger collection format (eg, "csv", "tsv",
+   *                         "pipes"). See the
+   *                         <a href="http://swagger.io/specification/#parameter-object-44">
+   *                         OpenAPI Spec</a> for more details.
+   * @return An object that will be correctly formatted by Feign.
+   */
+  public static Object encodeCollection(Collection<?> parameters,
+                                     String collectionFormat) {
+    if (parameters == null) {
+      return parameters;
+    }
+    List<String> stringValues = new ArrayList<>(parameters.size());
+    for (Object parameter : parameters) {
+      // ignore null values (same behavior as Feign)
+      if (parameter != null) {
+        stringValues.add(encode(parameter));
+      }
+    }
+    // Feign natively handles single-element lists and the "multi" format.
+    if (stringValues.size() < 2 || "multi".equals(collectionFormat)) {
+      return stringValues;
+    }
+    // Otherwise return a formatted String
+    String[] stringArray = stringValues.toArray(new String[0]);
+    switch (collectionFormat) {
+      case "csv":
+      default:
+        return StringUtil.join(stringArray, ",");
+      case "ssv":
+        return StringUtil.join(stringArray, " ");
+      case "tsv":
+        return StringUtil.join(stringArray, "\t");
+      case "pipes":
+        return StringUtil.join(stringArray, "|");
+    }
+  }
+
+  /**
+   * URL encode a single query parameter.
+   * @param parameter The query parameter to encode. This object will not be
+   *                  changed.
+   * @return The URL encoded string representation of the parameter. If the
+   *         parameter is null, returns null.
+   */
+  public static String encode(Object parameter) {
+    if (parameter == null) {
+      return null;
+    }
+    try {
+      return URLEncoder.encode(parameter.toString(), "UTF-8").replaceAll("\\+", "%20");
+    } catch (UnsupportedEncodingException e) {
+      // Should never happen, UTF-8 is always supported
+      throw new RuntimeException(e);
+    }
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ParamExpander.java

@@ -0,0 +1,22 @@
+package org.openapitools.client;
+
+import feign.Param;
+
+import java.text.DateFormat;
+import java.util.Date;
+
+/**
+ * Param Expander to convert {@link Date} to RFC3339
+ */
+public class ParamExpander implements Param.Expander {
+
+  private static final DateFormat dateformat = new RFC3339DateFormat();
+
+  @Override
+  public String expand(Object value) {
+    if (value instanceof Date) {
+      return dateformat.format(value);
+    }
+    return value.toString();
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/RFC3339DateFormat.java

@@ -0,0 +1,55 @@
+/*
+ * OpenAPI Petstore
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * 
+ *
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Do not edit the class manually.
+ */
+
+package org.openapitools.client;
+
+import com.fasterxml.jackson.databind.util.StdDateFormat;
+
+import java.text.DateFormat;
+import java.text.FieldPosition;
+import java.text.ParsePosition;
+import java.util.Date;
+import java.util.GregorianCalendar;
+import java.util.TimeZone;
+
+public class RFC3339DateFormat extends DateFormat {
+  private static final long serialVersionUID = 1L;
+  private static final TimeZone TIMEZONE_Z = TimeZone.getTimeZone("UTC");
+
+  private final StdDateFormat fmt = new StdDateFormat()
+          .withTimeZone(TIMEZONE_Z)
+          .withColonInTimeZone(true);
+
+  public RFC3339DateFormat() {
+    this.calendar = new GregorianCalendar();
+  }
+
+  @Override
+  public Date parse(String source) {
+    return parse(source, new ParsePosition(0));
+  }
+
+  @Override
+  public Date parse(String source, ParsePosition pos) {
+    return fmt.parse(source, pos);
+  }
+
+  @Override
+  public StringBuffer format(Date date, StringBuffer toAppendTo, FieldPosition fieldPosition) {
+    return fmt.format(date, toAppendTo, fieldPosition);
+  }
+
+  @Override
+  public Object clone() {
+    return this;
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ServerConfiguration.java

@@ -0,0 +1,58 @@
+package org.openapitools.client;
+
+import java.util.Map;
+
+/**
+ * Representing a Server configuration.
+ */
+public class ServerConfiguration {
+    public String URL;
+    public String description;
+    public Map<String, ServerVariable> variables;
+
+    /**
+     * @param URL A URL to the target host.
+     * @param description A describtion of the host designated by the URL.
+     * @param variables A map between a variable name and its value. The value is used for substitution in the server's URL template.
+     */
+    public ServerConfiguration(String URL, String description, Map<String, ServerVariable> variables) {
+        this.URL = URL;
+        this.description = description;
+        this.variables = variables;
+    }
+
+    /**
+     * Format URL template using given variables.
+     *
+     * @param variables A map between a variable name and its value.
+     * @return Formatted URL.
+     */
+    public String URL(Map<String, String> variables) {
+        String url = this.URL;
+
+        // go through variables and replace placeholders
+        for (Map.Entry<String, ServerVariable> variable: this.variables.entrySet()) {
+            String name = variable.getKey();
+            ServerVariable serverVariable = variable.getValue();
+            String value = serverVariable.defaultValue;
+
+            if (variables != null && variables.containsKey(name)) {
+                value = variables.get(name);
+                if (serverVariable.enumValues.size() > 0 && !serverVariable.enumValues.contains(value)) {
+                    throw new RuntimeException("The variable " + name + " in the server URL has invalid value " + value + ".");
+                }
+            }
+            url = url.replaceAll("\\{" + name + "\\}", value);
+        }
+        return url;
+    }
+
+    /**
+     * Format URL template using default server variables.
+     *
+     * @return Formatted URL.
+     */
+    public String URL() {
+        return URL(null);
+    }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ServerVariable.java

@@ -0,0 +1,23 @@
+package org.openapitools.client;
+
+import java.util.HashSet;
+
+/**
+ * Representing a Server Variable for server URL template substitution.
+ */
+public class ServerVariable {
+    public String description;
+    public String defaultValue;
+    public HashSet<String> enumValues = null;
+
+    /**
+     * @param description A description for the server variable.
+     * @param defaultValue The default value to use for substitution.
+     * @param enumValues An enumeration of string values to be used if the substitution options are from a limited set.
+     */
+    public ServerVariable(String description, String defaultValue, HashSet<String> enumValues) {
+        this.description = description;
+        this.defaultValue = defaultValue;
+        this.enumValues = enumValues;
+    }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/StringUtil.java

@@ -0,0 +1,83 @@
+/*
+ * OpenAPI Petstore
+ * This spec is mainly for testing Petstore server and contains fake endpoints, models. Please do not use this for any other purpose. Special characters: \" \\
+ *
+ * The version of the OpenAPI document: 1.0.0
+ * 
+ *
+ * NOTE: This class is auto generated by OpenAPI Generator (https://openapi-generator.tech).
+ * https://openapi-generator.tech
+ * Do not edit the class manually.
+ */
+
+
+package org.openapitools.client;
+
+import java.util.Collection;
+import java.util.Iterator;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class StringUtil {
+  /**
+   * Check if the given array contains the given value (with case-insensitive comparison).
+   *
+   * @param array The array
+   * @param value The value to search
+   * @return true if the array contains the value
+   */
+  public static boolean containsIgnoreCase(String[] array, String value) {
+    for (String str : array) {
+      if (value == null && str == null) {
+        return true;
+      }
+      if (value != null && value.equalsIgnoreCase(str)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  /**
+   * Join an array of strings with the given separator.
+   * <p>
+   * Note: This might be replaced by utility method from commons-lang or guava someday
+   * if one of those libraries is added as dependency.
+   * </p>
+   *
+   * @param array     The array of strings
+   * @param separator The separator
+   * @return the resulting string
+   */
+  public static String join(String[] array, String separator) {
+    int len = array.length;
+    if (len == 0) {
+      return "";
+    }
+
+    StringBuilder out = new StringBuilder();
+    out.append(array[0]);
+    for (int i = 1; i < len; i++) {
+      out.append(separator).append(array[i]);
+    }
+    return out.toString();
+  }
+
+  /**
+   * Join a list of strings with the given separator.
+   *
+   * @param list      The list of strings
+   * @param separator The separator
+   * @return the resulting string
+   */
+  public static String join(Collection<String> list, String separator) {
+    Iterator<String> iterator = list.iterator();
+    StringBuilder out = new StringBuilder();
+    if (iterator.hasNext()) {
+      out.append(iterator.next());
+    }
+    while (iterator.hasNext()) {
+      out.append(separator).append(iterator.next());
+    }
+    return out.toString();
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/AnotherFakeApi.java

@@ -0,0 +1,30 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import org.openapitools.client.model.Client;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface AnotherFakeApi extends ApiClient.Api {
+
+
+  /**
+   * To test special tags
+   * To test special tags and operation ID starting with number
+   * @param body client model (required)
+   * @return Client
+   */
+  @RequestLine("PATCH /another-fake/dummy")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  Client call123testSpecialTags(Client body);
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/FakeApi.java

@@ -0,0 +1,422 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import java.math.BigDecimal;
+import org.openapitools.client.model.Client;
+import java.io.File;
+import org.openapitools.client.model.FileSchemaTestClass;
+import org.threeten.bp.LocalDate;
+import org.threeten.bp.OffsetDateTime;
+import org.openapitools.client.model.OuterComposite;
+import org.openapitools.client.model.User;
+import org.openapitools.client.model.XmlItem;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface FakeApi extends ApiClient.Api {
+
+
+  /**
+   * creates an XmlItem
+   * this route creates an XmlItem
+   * @param xmlItem XmlItem Body (required)
+   */
+  @RequestLine("POST /fake/create_xml_item")
+  @Headers({
+    "Content-Type: application/xml",
+    "Accept: application/json",
+  })
+  void createXmlItem(XmlItem xmlItem);
+
+  /**
+   * 
+   * Test serialization of outer boolean types
+   * @param body Input boolean as post body (optional)
+   * @return Boolean
+   */
+  @RequestLine("POST /fake/outer/boolean")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: */*",
+  })
+  Boolean fakeOuterBooleanSerialize(Boolean body);
+
+  /**
+   * 
+   * Test serialization of object with outer number type
+   * @param body Input composite as post body (optional)
+   * @return OuterComposite
+   */
+  @RequestLine("POST /fake/outer/composite")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: */*",
+  })
+  OuterComposite fakeOuterCompositeSerialize(OuterComposite body);
+
+  /**
+   * 
+   * Test serialization of outer number types
+   * @param body Input number as post body (optional)
+   * @return BigDecimal
+   */
+  @RequestLine("POST /fake/outer/number")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: */*",
+  })
+  BigDecimal fakeOuterNumberSerialize(BigDecimal body);
+
+  /**
+   * 
+   * Test serialization of outer string types
+   * @param body Input string as post body (optional)
+   * @return String
+   */
+  @RequestLine("POST /fake/outer/string")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: */*",
+  })
+  String fakeOuterStringSerialize(String body);
+
+  /**
+   * 
+   * For this test, the body for this request much reference a schema named `File`.
+   * @param body  (required)
+   */
+  @RequestLine("PUT /fake/body-with-file-schema")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  void testBodyWithFileSchema(FileSchemaTestClass body);
+
+  /**
+   * 
+   * 
+   * @param query  (required)
+   * @param body  (required)
+   */
+  @RequestLine("PUT /fake/body-with-query-params?query={query}")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  void testBodyWithQueryParams(@Param("query") String query, User body);
+
+  /**
+   * 
+   * 
+   * Note, this is equivalent to the other <code>testBodyWithQueryParams</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link TestBodyWithQueryParamsQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param body  (required)
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>query -  (required)</li>
+   *   </ul>
+   */
+  @RequestLine("PUT /fake/body-with-query-params?query={query}")
+  @Headers({
+  "Content-Type: application/json",
+  "Accept: application/json",
+  })
+  void testBodyWithQueryParams(User body, @QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>testBodyWithQueryParams</code> method in a fluent style.
+   */
+  public static class TestBodyWithQueryParamsQueryParams extends HashMap<String, Object> {
+    public TestBodyWithQueryParamsQueryParams query(final String value) {
+      put("query", EncodingUtils.encode(value));
+      return this;
+    }
+  }
+
+  /**
+   * To test \&quot;client\&quot; model
+   * To test \&quot;client\&quot; model
+   * @param body client model (required)
+   * @return Client
+   */
+  @RequestLine("PATCH /fake")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  Client testClientModel(Client body);
+
+  /**
+   * Fake endpoint for testing various parameters  假端點  偽のエンドポイント  가짜 엔드 포인트
+   * Fake endpoint for testing various parameters  假端點  偽のエンドポイント  가짜 엔드 포인트
+   * @param number None (required)
+   * @param _double None (required)
+   * @param patternWithoutDelimiter None (required)
+   * @param _byte None (required)
+   * @param integer None (optional)
+   * @param int32 None (optional)
+   * @param int64 None (optional)
+   * @param _float None (optional)
+   * @param string None (optional)
+   * @param binary None (optional)
+   * @param date None (optional)
+   * @param dateTime None (optional)
+   * @param password None (optional)
+   * @param paramCallback None (optional)
+   */
+  @RequestLine("POST /fake")
+  @Headers({
+    "Content-Type: application/x-www-form-urlencoded",
+    "Accept: application/json",
+  })
+  void testEndpointParameters(@Param("number") BigDecimal number, @Param("_double") Double _double, @Param("patternWithoutDelimiter") String patternWithoutDelimiter, @Param("_byte") byte[] _byte, @Param("integer") Integer integer, @Param("int32") Integer int32, @Param("int64") Long int64, @Param("_float") Float _float, @Param("string") String string, @Param("binary") File binary, @Param("date") LocalDate date, @Param("dateTime") OffsetDateTime dateTime, @Param("password") String password, @Param("paramCallback") String paramCallback);
+
+  /**
+   * To test enum parameters
+   * To test enum parameters
+   * @param enumHeaderStringArray Header parameter enum test (string array) (optional)
+   * @param enumHeaderString Header parameter enum test (string) (optional, default to -efg)
+   * @param enumQueryStringArray Query parameter enum test (string array) (optional)
+   * @param enumQueryString Query parameter enum test (string) (optional, default to -efg)
+   * @param enumQueryInteger Query parameter enum test (double) (optional)
+   * @param enumQueryDouble Query parameter enum test (double) (optional)
+   * @param enumFormStringArray Form parameter enum test (string array) (optional)
+   * @param enumFormString Form parameter enum test (string) (optional, default to -efg)
+   */
+  @RequestLine("GET /fake?enum_query_string_array={enumQueryStringArray}&enum_query_string={enumQueryString}&enum_query_integer={enumQueryInteger}&enum_query_double={enumQueryDouble}")
+  @Headers({
+    "Content-Type: application/x-www-form-urlencoded",
+    "Accept: application/json",
+    "enum_header_string_array: {enumHeaderStringArray}",
+    
+    "enum_header_string: {enumHeaderString}"
+  })
+  void testEnumParameters(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enumQueryStringArray") List<String> enumQueryStringArray, @Param("enumQueryString") String enumQueryString, @Param("enumQueryInteger") Integer enumQueryInteger, @Param("enumQueryDouble") Double enumQueryDouble, @Param("enumFormStringArray") List<String> enumFormStringArray, @Param("enumFormString") String enumFormString);
+
+  /**
+   * To test enum parameters
+   * To test enum parameters
+   * Note, this is equivalent to the other <code>testEnumParameters</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link TestEnumParametersQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param enumHeaderStringArray Header parameter enum test (string array) (optional)
+   * @param enumHeaderString Header parameter enum test (string) (optional, default to -efg)
+   * @param enumFormStringArray Form parameter enum test (string array) (optional)
+   * @param enumFormString Form parameter enum test (string) (optional, default to -efg)
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>enumQueryStringArray - Query parameter enum test (string array) (optional)</li>
+   *   <li>enumQueryString - Query parameter enum test (string) (optional, default to -efg)</li>
+   *   <li>enumQueryInteger - Query parameter enum test (double) (optional)</li>
+   *   <li>enumQueryDouble - Query parameter enum test (double) (optional)</li>
+   *   </ul>
+   */
+  @RequestLine("GET /fake?enum_query_string_array={enumQueryStringArray}&enum_query_string={enumQueryString}&enum_query_integer={enumQueryInteger}&enum_query_double={enumQueryDouble}")
+  @Headers({
+  "Content-Type: application/x-www-form-urlencoded",
+  "Accept: application/json",
+      "enum_header_string_array: {enumHeaderStringArray}",
+      
+      "enum_header_string: {enumHeaderString}"
+  })
+  void testEnumParameters(@Param("enumHeaderStringArray") List<String> enumHeaderStringArray, @Param("enumHeaderString") String enumHeaderString, @Param("enumFormStringArray") List<String> enumFormStringArray, @Param("enumFormString") String enumFormString, @QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>testEnumParameters</code> method in a fluent style.
+   */
+  public static class TestEnumParametersQueryParams extends HashMap<String, Object> {
+    public TestEnumParametersQueryParams enumQueryStringArray(final List<String> value) {
+      put("enum_query_string_array", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+    public TestEnumParametersQueryParams enumQueryString(final String value) {
+      put("enum_query_string", EncodingUtils.encode(value));
+      return this;
+    }
+    public TestEnumParametersQueryParams enumQueryInteger(final Integer value) {
+      put("enum_query_integer", EncodingUtils.encode(value));
+      return this;
+    }
+    public TestEnumParametersQueryParams enumQueryDouble(final Double value) {
+      put("enum_query_double", EncodingUtils.encode(value));
+      return this;
+    }
+  }
+
+  /**
+   * Fake endpoint to test group parameters (optional)
+   * Fake endpoint to test group parameters (optional)
+   * @param requiredStringGroup Required String in group parameters (required)
+   * @param requiredBooleanGroup Required Boolean in group parameters (required)
+   * @param requiredInt64Group Required Integer in group parameters (required)
+   * @param stringGroup String in group parameters (optional)
+   * @param booleanGroup Boolean in group parameters (optional)
+   * @param int64Group Integer in group parameters (optional)
+   */
+  @RequestLine("DELETE /fake?required_string_group={requiredStringGroup}&required_int64_group={requiredInt64Group}&string_group={stringGroup}&int64_group={int64Group}")
+  @Headers({
+    "Accept: application/json",
+    "required_boolean_group: {requiredBooleanGroup}",
+    
+    "boolean_group: {booleanGroup}"
+  })
+  void testGroupParameters(@Param("requiredStringGroup") Integer requiredStringGroup, @Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("requiredInt64Group") Long requiredInt64Group, @Param("stringGroup") Integer stringGroup, @Param("booleanGroup") Boolean booleanGroup, @Param("int64Group") Long int64Group);
+
+  /**
+   * Fake endpoint to test group parameters (optional)
+   * Fake endpoint to test group parameters (optional)
+   * Note, this is equivalent to the other <code>testGroupParameters</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link TestGroupParametersQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param requiredBooleanGroup Required Boolean in group parameters (required)
+   * @param booleanGroup Boolean in group parameters (optional)
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>requiredStringGroup - Required String in group parameters (required)</li>
+   *   <li>requiredInt64Group - Required Integer in group parameters (required)</li>
+   *   <li>stringGroup - String in group parameters (optional)</li>
+   *   <li>int64Group - Integer in group parameters (optional)</li>
+   *   </ul>
+   */
+  @RequestLine("DELETE /fake?required_string_group={requiredStringGroup}&required_int64_group={requiredInt64Group}&string_group={stringGroup}&int64_group={int64Group}")
+  @Headers({
+  "Accept: application/json",
+      "required_boolean_group: {requiredBooleanGroup}",
+      
+      "boolean_group: {booleanGroup}"
+  })
+  void testGroupParameters(@Param("requiredBooleanGroup") Boolean requiredBooleanGroup, @Param("booleanGroup") Boolean booleanGroup, @QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>testGroupParameters</code> method in a fluent style.
+   */
+  public static class TestGroupParametersQueryParams extends HashMap<String, Object> {
+    public TestGroupParametersQueryParams requiredStringGroup(final Integer value) {
+      put("required_string_group", EncodingUtils.encode(value));
+      return this;
+    }
+    public TestGroupParametersQueryParams requiredInt64Group(final Long value) {
+      put("required_int64_group", EncodingUtils.encode(value));
+      return this;
+    }
+    public TestGroupParametersQueryParams stringGroup(final Integer value) {
+      put("string_group", EncodingUtils.encode(value));
+      return this;
+    }
+    public TestGroupParametersQueryParams int64Group(final Long value) {
+      put("int64_group", EncodingUtils.encode(value));
+      return this;
+    }
+  }
+
+  /**
+   * test inline additionalProperties
+   * 
+   * @param param request body (required)
+   */
+  @RequestLine("POST /fake/inline-additionalProperties")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  void testInlineAdditionalProperties(Map<String, String> param);
+
+  /**
+   * test json serialization of form data
+   * 
+   * @param param field1 (required)
+   * @param param2 field2 (required)
+   */
+  @RequestLine("GET /fake/jsonFormData")
+  @Headers({
+    "Content-Type: application/x-www-form-urlencoded",
+    "Accept: application/json",
+  })
+  void testJsonFormData(@Param("param") String param, @Param("param2") String param2);
+
+  /**
+   * 
+   * To test the collection format in query parameters
+   * @param pipe  (required)
+   * @param ioutil  (required)
+   * @param http  (required)
+   * @param url  (required)
+   * @param context  (required)
+   */
+  @RequestLine("PUT /fake/test-query-paramters?pipe={pipe}&ioutil={ioutil}&http={http}&url={url}&context={context}")
+  @Headers({
+    "Accept: application/json",
+  })
+  void testQueryParameterCollectionFormat(@Param("pipe") List<String> pipe, @Param("ioutil") List<String> ioutil, @Param("http") List<String> http, @Param("url") List<String> url, @Param("context") List<String> context);
+
+  /**
+   * 
+   * To test the collection format in query parameters
+   * Note, this is equivalent to the other <code>testQueryParameterCollectionFormat</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link TestQueryParameterCollectionFormatQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>pipe -  (required)</li>
+   *   <li>ioutil -  (required)</li>
+   *   <li>http -  (required)</li>
+   *   <li>url -  (required)</li>
+   *   <li>context -  (required)</li>
+   *   </ul>
+   */
+  @RequestLine("PUT /fake/test-query-paramters?pipe={pipe}&ioutil={ioutil}&http={http}&url={url}&context={context}")
+  @Headers({
+  "Accept: application/json",
+  })
+  void testQueryParameterCollectionFormat(@QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>testQueryParameterCollectionFormat</code> method in a fluent style.
+   */
+  public static class TestQueryParameterCollectionFormatQueryParams extends HashMap<String, Object> {
+    public TestQueryParameterCollectionFormatQueryParams pipe(final List<String> value) {
+      put("pipe", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+    public TestQueryParameterCollectionFormatQueryParams ioutil(final List<String> value) {
+      put("ioutil", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+    public TestQueryParameterCollectionFormatQueryParams http(final List<String> value) {
+      put("http", EncodingUtils.encodeCollection(value, "ssv"));
+      return this;
+    }
+    public TestQueryParameterCollectionFormatQueryParams url(final List<String> value) {
+      put("url", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+    public TestQueryParameterCollectionFormatQueryParams context(final List<String> value) {
+      put("context", EncodingUtils.encodeCollection(value, "multi"));
+      return this;
+    }
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/FakeClassnameTags123Api.java

@@ -0,0 +1,30 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import org.openapitools.client.model.Client;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface FakeClassnameTags123Api extends ApiClient.Api {
+
+
+  /**
+   * To test class name in snake case
+   * To test class name in snake case
+   * @param body client model (required)
+   * @return Client
+   */
+  @RequestLine("PATCH /fake_classname_test")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  Client testClassname(Client body);
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/PetApi.java

@@ -0,0 +1,201 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import java.io.File;
+import org.openapitools.client.model.ModelApiResponse;
+import org.openapitools.client.model.Pet;
+import java.util.Set;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface PetApi extends ApiClient.Api {
+
+
+  /**
+   * Add a new pet to the store
+   * 
+   * @param body Pet object that needs to be added to the store (required)
+   */
+  @RequestLine("POST /pet")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  void addPet(Pet body);
+
+  /**
+   * Deletes a pet
+   * 
+   * @param petId Pet id to delete (required)
+   * @param apiKey  (optional)
+   */
+  @RequestLine("DELETE /pet/{petId}")
+  @Headers({
+    "Accept: application/json",
+    "api_key: {apiKey}"
+  })
+  void deletePet(@Param("petId") Long petId, @Param("apiKey") String apiKey);
+
+  /**
+   * Finds Pets by status
+   * Multiple status values can be provided with comma separated strings
+   * @param status Status values that need to be considered for filter (required)
+   * @return List<Pet>
+   */
+  @RequestLine("GET /pet/findByStatus?status={status}")
+  @Headers({
+    "Accept: application/json",
+  })
+  List<Pet> findPetsByStatus(@Param("status") List<String> status);
+
+  /**
+   * Finds Pets by status
+   * Multiple status values can be provided with comma separated strings
+   * Note, this is equivalent to the other <code>findPetsByStatus</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link FindPetsByStatusQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>status - Status values that need to be considered for filter (required)</li>
+   *   </ul>
+   * @return List&lt;Pet&gt;
+   */
+  @RequestLine("GET /pet/findByStatus?status={status}")
+  @Headers({
+  "Accept: application/json",
+  })
+  List<Pet> findPetsByStatus(@QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>findPetsByStatus</code> method in a fluent style.
+   */
+  public static class FindPetsByStatusQueryParams extends HashMap<String, Object> {
+    public FindPetsByStatusQueryParams status(final List<String> value) {
+      put("status", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+  }
+
+  /**
+   * Finds Pets by tags
+   * Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.
+   * @param tags Tags to filter by (required)
+   * @return Set&lt;Pet&gt;
+   */
+  @RequestLine("GET /pet/findByTags?tags={tags}")
+  @Headers({
+    "Accept: application/json",
+  })
+  Set<Pet> findPetsByTags(@Param("tags") Set<String> tags);
+
+  /**
+   * Finds Pets by tags
+   * Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.
+   * Note, this is equivalent to the other <code>findPetsByTags</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link FindPetsByTagsQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>tags - Tags to filter by (required)</li>
+   *   </ul>
+   * @return Set&lt;Pet&gt;
+   */
+  @RequestLine("GET /pet/findByTags?tags={tags}")
+  @Headers({
+  "Accept: application/json",
+  })
+  Set<Pet> findPetsByTags(@QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>findPetsByTags</code> method in a fluent style.
+   */
+  public static class FindPetsByTagsQueryParams extends HashMap<String, Object> {
+    public FindPetsByTagsQueryParams tags(final Set<String> value) {
+      put("tags", EncodingUtils.encodeCollection(value, "csv"));
+      return this;
+    }
+  }
+
+  /**
+   * Find pet by ID
+   * Returns a single pet
+   * @param petId ID of pet to return (required)
+   * @return Pet
+   */
+  @RequestLine("GET /pet/{petId}")
+  @Headers({
+    "Accept: application/json",
+  })
+  Pet getPetById(@Param("petId") Long petId);
+
+  /**
+   * Update an existing pet
+   * 
+   * @param body Pet object that needs to be added to the store (required)
+   */
+  @RequestLine("PUT /pet")
+  @Headers({
+    "Content-Type: application/json",
+    "Accept: application/json",
+  })
+  void updatePet(Pet body);
+
+  /**
+   * Updates a pet in the store with form data
+   * 
+   * @param petId ID of pet that needs to be updated (required)
+   * @param name Updated name of the pet (optional)
+   * @param status Updated status of the pet (optional)
+   */
+  @RequestLine("POST /pet/{petId}")
+  @Headers({
+    "Content-Type: application/x-www-form-urlencoded",
+    "Accept: application/json",
+  })
+  void updatePetWithForm(@Param("petId") Long petId, @Param("name") String name, @Param("status") String status);
+
+  /**
+   * uploads an image
+   * 
+   * @param petId ID of pet to update (required)
+   * @param additionalMetadata Additional data to pass to server (optional)
+   * @param file file to upload (optional)
+   * @return ModelApiResponse
+   */
+  @RequestLine("POST /pet/{petId}/uploadImage")
+  @Headers({
+    "Content-Type: multipart/form-data",
+    "Accept: application/json",
+  })
+  ModelApiResponse uploadFile(@Param("petId") Long petId, @Param("additionalMetadata") String additionalMetadata, @Param("file") File file);
+
+  /**
+   * uploads an image (required)
+   * 
+   * @param petId ID of pet to update (required)
+   * @param requiredFile file to upload (required)
+   * @param additionalMetadata Additional data to pass to server (optional)
+   * @return ModelApiResponse
+   */
+  @RequestLine("POST /fake/{petId}/uploadImageWithRequiredFile")
+  @Headers({
+    "Content-Type: multipart/form-data",
+    "Accept: application/json",
+  })
+  ModelApiResponse uploadFileWithRequiredFile(@Param("petId") Long petId, @Param("requiredFile") File requiredFile, @Param("additionalMetadata") String additionalMetadata);
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/StoreApi.java

@@ -0,0 +1,64 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import org.openapitools.client.model.Order;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface StoreApi extends ApiClient.Api {
+
+
+  /**
+   * Delete purchase order by ID
+   * For valid response try integer IDs with value < 1000. Anything above 1000 or nonintegers will generate API errors
+   * @param orderId ID of the order that needs to be deleted (required)
+   */
+  @RequestLine("DELETE /store/order/{orderId}")
+  @Headers({
+    "Accept: application/json",
+  })
+  void deleteOrder(@Param("orderId") String orderId);
+
+  /**
+   * Returns pet inventories by status
+   * Returns a map of status codes to quantities
+   * @return Map<String, Integer>
+   */
+  @RequestLine("GET /store/inventory")
+  @Headers({
+    "Accept: application/json",
+  })
+  Map<String, Integer> getInventory();
+
+  /**
+   * Find purchase order by ID
+   * For valid response try integer IDs with value &lt;&#x3D; 5 or &gt; 10. Other values will generated exceptions
+   * @param orderId ID of pet that needs to be fetched (required)
+   * @return Order
+   */
+  @RequestLine("GET /store/order/{orderId}")
+  @Headers({
+    "Accept: application/json",
+  })
+  Order getOrderById(@Param("orderId") Long orderId);
+
+  /**
+   * Place an order for a pet
+   * 
+   * @param body order placed for purchasing the pet (required)
+   * @return Order
+   */
+  @RequestLine("POST /store/order")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: application/json",
+  })
+  Order placeOrder(Order body);
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/api/UserApi.java

@@ -0,0 +1,149 @@
+package org.openapitools.client.api;
+
+import org.openapitools.client.ApiClient;
+import org.openapitools.client.EncodingUtils;
+
+import org.openapitools.client.model.User;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import feign.*;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public interface UserApi extends ApiClient.Api {
+
+
+  /**
+   * Create user
+   * This can only be done by the logged in user.
+   * @param body Created user object (required)
+   */
+  @RequestLine("POST /user")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: application/json",
+  })
+  void createUser(User body);
+
+  /**
+   * Creates list of users with given input array
+   * 
+   * @param body List of user object (required)
+   */
+  @RequestLine("POST /user/createWithArray")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: application/json",
+  })
+  void createUsersWithArrayInput(List<User> body);
+
+  /**
+   * Creates list of users with given input array
+   * 
+   * @param body List of user object (required)
+   */
+  @RequestLine("POST /user/createWithList")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: application/json",
+  })
+  void createUsersWithListInput(List<User> body);
+
+  /**
+   * Delete user
+   * This can only be done by the logged in user.
+   * @param username The name that needs to be deleted (required)
+   */
+  @RequestLine("DELETE /user/{username}")
+  @Headers({
+    "Accept: application/json",
+  })
+  void deleteUser(@Param("username") String username);
+
+  /**
+   * Get user by user name
+   * 
+   * @param username The name that needs to be fetched. Use user1 for testing. (required)
+   * @return User
+   */
+  @RequestLine("GET /user/{username}")
+  @Headers({
+    "Accept: application/json",
+  })
+  User getUserByName(@Param("username") String username);
+
+  /**
+   * Logs user into the system
+   * 
+   * @param username The user name for login (required)
+   * @param password The password for login in clear text (required)
+   * @return String
+   */
+  @RequestLine("GET /user/login?username={username}&password={password}")
+  @Headers({
+    "Accept: application/json",
+  })
+  String loginUser(@Param("username") String username, @Param("password") String password);
+
+  /**
+   * Logs user into the system
+   * 
+   * Note, this is equivalent to the other <code>loginUser</code> method,
+   * but with the query parameters collected into a single Map parameter. This
+   * is convenient for services with optional query parameters, especially when
+   * used with the {@link LoginUserQueryParams} class that allows for
+   * building up this map in a fluent style.
+   * @param queryParams Map of query parameters as name-value pairs
+   *   <p>The following elements may be specified in the query map:</p>
+   *   <ul>
+   *   <li>username - The user name for login (required)</li>
+   *   <li>password - The password for login in clear text (required)</li>
+   *   </ul>
+   * @return String
+   */
+  @RequestLine("GET /user/login?username={username}&password={password}")
+  @Headers({
+  "Accept: application/json",
+  })
+  String loginUser(@QueryMap(encoded=true) Map<String, Object> queryParams);
+
+  /**
+   * A convenience class for generating query parameters for the
+   * <code>loginUser</code> method in a fluent style.
+   */
+  public static class LoginUserQueryParams extends HashMap<String, Object> {
+    public LoginUserQueryParams username(final String value) {
+      put("username", EncodingUtils.encode(value));
+      return this;
+    }
+    public LoginUserQueryParams password(final String value) {
+      put("password", EncodingUtils.encode(value));
+      return this;
+    }
+  }
+
+  /**
+   * Logs out current logged in user session
+   * 
+   */
+  @RequestLine("GET /user/logout")
+  @Headers({
+    "Accept: application/json",
+  })
+  void logoutUser();
+
+  /**
+   * Updated user
+   * This can only be done by the logged in user.
+   * @param username name that need to be deleted (required)
+   * @param body Updated user object (required)
+   */
+  @RequestLine("PUT /user/{username}")
+  @Headers({
+    "Content-Type: */*",
+    "Accept: application/json",
+  })
+  void updateUser(@Param("username") String username, User body);
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/ApiKeyAuth.java

@@ -0,0 +1,43 @@
+package org.openapitools.client.auth;
+
+import feign.RequestInterceptor;
+import feign.RequestTemplate;
+
+public class ApiKeyAuth implements RequestInterceptor {
+    private final String location;
+    private final String paramName;
+
+    private String apiKey;
+
+    public ApiKeyAuth(String location, String paramName) {
+        this.location = location;
+        this.paramName = paramName;
+    }
+
+    public String getLocation() {
+        return location;
+    }
+
+    public String getParamName() {
+        return paramName;
+    }
+
+    public String getApiKey() {
+        return apiKey;
+    }
+
+    public void setApiKey(String apiKey) {
+        this.apiKey = apiKey;
+    }
+
+    @Override
+    public void apply(RequestTemplate template) {
+        if ("query".equals(location)) {
+            template.query(paramName, apiKey);
+        } else if ("header".equals(location)) {
+            template.header(paramName, apiKey);
+        } else if ("cookie".equals(location)) {
+            template.header("Cookie", String.format("%s=%s", paramName, apiKey));
+        }
+    }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/HttpBasicAuth.java

@@ -0,0 +1,41 @@
+package org.openapitools.client.auth;
+
+import feign.RequestInterceptor;
+import feign.RequestTemplate;
+import feign.auth.BasicAuthRequestInterceptor;
+
+/**
+ * An interceptor that adds the request header needed to use HTTP basic authentication.
+ */
+public class HttpBasicAuth implements RequestInterceptor {
+
+    private String username;
+    private String password;
+    
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+
+    public void setCredentials(String username, String password) {
+        this.username = username;
+        this.password = password;
+    }
+
+  @Override
+  public void apply(RequestTemplate template) {
+      RequestInterceptor requestInterceptor = new BasicAuthRequestInterceptor(username, password);
+      requestInterceptor.apply(template);
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/HttpBearerAuth.java

@@ -0,0 +1,43 @@
+package org.openapitools.client.auth;
+
+import feign.RequestInterceptor;
+import feign.RequestTemplate;
+
+/**
+ * An interceptor that adds the request header needed to use HTTP bearer authentication.
+ */
+public class HttpBearerAuth implements RequestInterceptor {
+  private final String scheme;
+  private String bearerToken;
+
+  public HttpBearerAuth(String scheme) {
+    this.scheme = scheme;
+  }
+
+  /**
+   * Gets the token, which together with the scheme, will be sent as the value of the Authorization header.
+   */
+  public String getBearerToken() {
+    return bearerToken;
+  }
+
+  /**
+   * Sets the token, which together with the scheme, will be sent as the value of the Authorization header.
+   */
+  public void setBearerToken(String bearerToken) {
+    this.bearerToken = bearerToken;
+  }
+
+  @Override
+  public void apply(RequestTemplate template) {
+    if(bearerToken == null) {
+      return;
+    }
+
+    template.header("Authorization", (scheme != null ? upperCaseBearer(scheme) + " " : "") + bearerToken);
+  }
+
+  private static String upperCaseBearer(String scheme) {
+    return ("bearer".equalsIgnoreCase(scheme)) ? "Bearer" : scheme;
+  }
+}

samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OAuth.java

@@ -0,0 +1,198 @@
+package org.openapitools.client.auth;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.Map;
+import java.util.Map.Entry;
+
+import org.apache.oltu.oauth2.client.HttpClient;
+import org.apache.oltu.oauth2.client.OAuthClient;
+import org.apache.oltu.oauth2.client.request.OAuthClientRequest;
+import org.apache.oltu.oauth2.client.request.OAuthClientRequest.AuthenticationRequestBuilder;
+import org.apache.oltu.oauth2.client.request.OAuthClientRequest.TokenRequestBuilder;
+import org.apache.oltu.oauth2.client.response.OAuthClientResponse;
+import org.apache.oltu.oauth2.client.response.OAuthClientResponseFactory;
+import org.apache.oltu.oauth2.client.response.OAuthJSONAccessTokenResponse;
+import org.apache.oltu.oauth2.common.exception.OAuthProblemException;
+import org.apache.oltu.oauth2.common.exception.OAuthSystemException;
+import org.apache.oltu.oauth2.common.message.types.GrantType;
+import org.apache.oltu.oauth2.common.token.BasicOAuthToken;
+
+import feign.Client;
+import feign.Request.HttpMethod;
+import feign.Request.Options;
+import feign.RequestInterceptor;
+import feign.RequestTemplate;
+import feign.Response;
+import feign.RetryableException;
+import feign.Util;
+import org.openapitools.client.StringUtil;
+
+
+public class OAuth implements RequestInterceptor {
+
+    static final int MILLIS_PER_SECOND = 1000;
+
+    public interface AccessTokenListener {
+        void notify(BasicOAuthToken token);
+    }
+
+    private volatile String accessToken;
+    private Long expirationTimeMillis;
+    private OAuthClient oauthClient;
+    private TokenRequestBuilder tokenRequestBuilder;
+    private AuthenticationRequestBuilder authenticationRequestBuilder;
+    private AccessTokenListener accessTokenListener;
+
+    public OAuth(Client client, TokenRequestBuilder requestBuilder) {
+        this.oauthClient = new OAuthClient(new OAuthFeignClient(client));
+        this.tokenRequestBuilder = requestBuilder;
+    }
+
+    public OAuth(Client client, OAuthFlow flow, String authorizationUrl, String tokenUrl, String scopes) {
+        this(client, OAuthClientRequest.tokenLocation(tokenUrl).setScope(scopes));
+
+        switch(flow) {
+        case accessCode:
+        case implicit:
+            tokenRequestBuilder.setGrantType(GrantType.AUTHORIZATION_CODE);
+            break;
+        case password:
+            tokenRequestBuilder.setGrantType(GrantType.PASSWORD);
+            break;
+        case application:
+            tokenRequestBuilder.setGrantType(GrantType.CLIENT_CREDENTIALS);
+            break;
+        default:
+            break;
+        }
+        authenticationRequestBuilder = OAuthClientRequest.authorizationLocation(authorizationUrl);
+    }
+
+    public OAuth(OAuthFlow flow, String authorizationUrl, String tokenUrl, String scopes) {
+        this(new Client.Default(null, null), flow, authorizationUrl, tokenUrl, scopes);
+    }
+
+    @Override
+    public void apply(RequestTemplate template) {
+        // If the request already have an authorization (eg. Basic auth), do nothing
+        if (template.headers().containsKey("Authorization")) {
+            return;
+        }
+        // If first time, get the token
+        if (expirationTimeMillis == null || System.currentTimeMillis() >= expirationTimeMillis) {
+            updateAccessToken(template);
+        }
+        if (getAccessToken() != null) {
+            template.header("Authorization", "Bearer " + getAccessToken());
+        }
+    }
+
+    public synchronized void updateAccessToken(RequestTemplate template) {
+        OAuthJSONAccessTokenResponse accessTokenResponse;
+        try {
+            accessTokenResponse = oauthClient.accessToken(tokenRequestBuilder.buildBodyMessage());
+        } catch (Exception e) {
+            throw new RetryableException(0, e.getMessage(), HttpMethod.POST, e, null, template.request());
+        }
+        if (accessTokenResponse != null && accessTokenResponse.getAccessToken() != null) {
+            setAccessToken(accessTokenResponse.getAccessToken(), accessTokenResponse.getExpiresIn());
+            if (accessTokenListener != null) {
+                accessTokenListener.notify((BasicOAuthToken) accessTokenResponse.getOAuthToken());
+            }
+        }
+    }
+
+    public synchronized void registerAccessTokenListener(AccessTokenListener accessTokenListener) {
+        this.accessTokenListener = accessTokenListener;
+    }
+
+    public synchronized String getAccessToken() {
+        return accessToken;
+    }
+
+    public synchronized void setAccessToken(String accessToken, Long expiresIn) {
+        this.accessToken = accessToken;
+        this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
+    }
+
+    public TokenRequestBuilder getTokenRequestBuilder() {
+        return tokenRequestBuilder;
+    }
+
+    public void setTokenRequestBuilder(TokenRequestBuilder tokenRequestBuilder) {
+        this.tokenRequestBuilder = tokenRequestBuilder;
+    }
+
+    public AuthenticationRequestBuilder getAuthenticationRequestBuilder() {
+        return authenticationRequestBuilder;
+    }
+
+    public void setAuthenticationRequestBuilder(AuthenticationRequestBuilder authenticationRequestBuilder) {
+        this.authenticationRequestBuilder = authenticationRequestBuilder;
+    }
+
+    public OAuthClient getOauthClient() {
+        return oauthClient;
+    }
+
+    public void setOauthClient(OAuthClient oauthClient) {
+        this.oauthClient = oauthClient;
+    }
+
+    public void setOauthClient(Client client) {
+        this.oauthClient = new OAuthClient( new OAuthFeignClient(client));
+    }
+
+    public static class OAuthFeignClient implements HttpClient {
+
+        private Client client;
+
+        public OAuthFeignClient() {
+            this.client = new Client.Default(null, null);
+        }
+
+        public OAuthFeignClient(Client client) {
+            this.client = client;
+        }
+
+        public <T extends OAuthClientResponse> T execute(OAuthClientRequest request, Map<String, String> headers,
+                String requestMethod, Class<T> responseClass)
+                        throws OAuthSystemException, OAuthProblemException {
+
+            RequestTemplate req = new RequestTemplate()
+                    .append(request.getLocationUri())
+                    .method(requestMethod)
+                    .body(request.getBody());
+
+            for (Entry<String, String> entry : headers.entrySet()) {
+                req.header(entry.getKey(), entry.getValue());
+            }
+            Response feignResponse;
+            String body = "";
+            try {
+                feignResponse = client.execute(req.request(), new Options());
+                body = Util.toString(feignResponse.body().asReader());
+            } catch (IOException e) {
+                throw new OAuthSystemException(e);
+            }
+
+            String contentType = null;
+            Collection<String> contentTypeHeader =  feignResponse.headers().get("Content-Type");
+            if(contentTypeHeader != null) {
+                contentType = StringUtil.join(contentTypeHeader.toArray(new String[0]), ";");
+            }
+
+            return OAuthClientResponseFactory.createCustomResponse(
+                    body,
+                    contentType,
+                    feignResponse.status(),
+                    responseClass
+            );
+        }
+
+        public void shutdown() {
+            // Nothing to do here
+        }
+    }
+}