[Java] better default value handling (#14130)

* add test for array default value

* update null return

* minor fixes

* move default value tests to echo api spec

* add new files

* remove unused files

* fix enum array default, add tests

* better array init

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

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

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

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

* revert the fix

* improve default value handling

* update native samples, add tests

* update samples

* fix tests

* use conditional test for timezone

* add tests to apache http client echo api

* add option to default container to null

* fix map default value

* minor refactoring

* update samples

* fix javadoc

* fix pom.xml

* add tests in java native echo client

* add java apache client echo tests

* fix test

* fix test

---------

Co-authored-by: Leonard Brünings <lord_damokles@gmx.net>

samples/client/echo_api/java/apache-httpclient/.openapi-generator/FILES

@@ -10,6 +10,7 @@ docs/BodyApi.md
 docs/Category.md
 docs/DataQuery.md
 docs/DataQueryAllOf.md
+docs/DefaultValue.md
 docs/PathApi.md
 docs/Pet.md
 docs/Query.md
@@ -46,6 +47,7 @@ src/main/java/org/openapitools/client/model/Bird.java
 src/main/java/org/openapitools/client/model/Category.java
 src/main/java/org/openapitools/client/model/DataQuery.java
 src/main/java/org/openapitools/client/model/DataQueryAllOf.java
+src/main/java/org/openapitools/client/model/DefaultValue.java
 src/main/java/org/openapitools/client/model/Pet.java
 src/main/java/org/openapitools/client/model/Query.java
 src/main/java/org/openapitools/client/model/Tag.java

samples/client/echo_api/java/apache-httpclient/README.md

@@ -122,6 +122,7 @@ Class | Method | HTTP request | Description
  - [Category](docs/Category.md)
  - [DataQuery](docs/DataQuery.md)
  - [DataQueryAllOf](docs/DataQueryAllOf.md)
+ - [DefaultValue](docs/DefaultValue.md)
  - [Pet](docs/Pet.md)
  - [Query](docs/Query.md)
  - [Tag](docs/Tag.md)

samples/client/echo_api/java/apache-httpclient/api/openapi.yaml

@@ -301,6 +301,47 @@ components:
       type: object
       xml:
         name: pet
+    DefaultValue:
+      description: to test the default value of properties
+      properties:
+        array_string_enum_default:
+          default:
+          - success
+          - failure
+          items:
+            enum:
+            - success
+            - failure
+            - unclassified
+            type: string
+          type: array
+        array_string_default:
+          default:
+          - failure
+          - skipped
+          items:
+            type: string
+          type: array
+        array_integer_default:
+          default:
+          - 1
+          - 3
+          items:
+            type: integer
+          type: array
+        array_string:
+          items:
+            type: string
+          type: array
+        array_string_nullable:
+          items:
+            type: string
+          nullable: true
+          type: array
+        string_nullable:
+          nullable: true
+          type: string
+      type: object
     Bird:
       properties:
         size:

samples/client/echo_api/java/apache-httpclient/docs/DefaultValue.md

@@ -0,0 +1,29 @@
+
+
+# DefaultValue
+
+to test the default value of properties
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**arrayStringEnumDefault** | [**List<ArrayStringEnumDefaultEnum>**](#List<ArrayStringEnumDefaultEnum>) |  |  [optional] |
+|**arrayStringDefault** | **List<String>** |  |  [optional] |
+|**arrayIntegerDefault** | **List<Integer>** |  |  [optional] |
+|**arrayString** | **List<String>** |  |  [optional] |
+|**arrayStringNullable** | **List<String>** |  |  [optional] |
+|**stringNullable** | **String** |  |  [optional] |
+
+
+
+## Enum: List<ArrayStringEnumDefaultEnum>
+
+| Name | Value |
+|---- | -----|
+| SUCCESS | "success" |
+| FAILURE | "failure" |
+| UNCLASSIFIED | "unclassified" |
+
+
+

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/DefaultValue.java

@@ -0,0 +1,496 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import java.util.Objects;
+import java.util.Arrays;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import com.fasterxml.jackson.annotation.JsonValue;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import org.openapitools.jackson.nullable.JsonNullable;
+import java.util.NoSuchElementException;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import java.io.UnsupportedEncodingException;
+import java.net.URLEncoder;
+import java.util.StringJoiner;
+
+/**
+ * to test the default value of properties
+ */
+@JsonPropertyOrder({
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_INTEGER_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_NULLABLE,
+  DefaultValue.JSON_PROPERTY_STRING_NULLABLE
+})
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class DefaultValue {
+  /**
+   * Gets or Sets arrayStringEnumDefault
+   */
+  public enum ArrayStringEnumDefaultEnum {
+    SUCCESS("success"),
+    
+    FAILURE("failure"),
+    
+    UNCLASSIFIED("unclassified");
+
+    private String value;
+
+    ArrayStringEnumDefaultEnum(String value) {
+      this.value = value;
+    }
+
+    @JsonValue
+    public String getValue() {
+      return value;
+    }
+
+    @Override
+    public String toString() {
+      return String.valueOf(value);
+    }
+
+    @JsonCreator
+    public static ArrayStringEnumDefaultEnum fromValue(String value) {
+      for (ArrayStringEnumDefaultEnum b : ArrayStringEnumDefaultEnum.values()) {
+        if (b.value.equals(value)) {
+          return b;
+        }
+      }
+      throw new IllegalArgumentException("Unexpected value '" + value + "'");
+    }
+  }
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT = "array_string_enum_default";
+  private List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_DEFAULT = "array_string_default";
+  private List<String> arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+
+  public static final String JSON_PROPERTY_ARRAY_INTEGER_DEFAULT = "array_integer_default";
+  private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+
+  public static final String JSON_PROPERTY_ARRAY_STRING = "array_string";
+  private List<String> arrayString = new ArrayList<>();
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_NULLABLE = "array_string_nullable";
+  private JsonNullable<List<String>> arrayStringNullable = JsonNullable.<List<String>>undefined();
+
+  public static final String JSON_PROPERTY_STRING_NULLABLE = "string_nullable";
+  private JsonNullable<String> stringNullable = JsonNullable.<String>undefined();
+
+  public DefaultValue() {
+  }
+
+  public DefaultValue arrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringEnumDefaultItem(ArrayStringEnumDefaultEnum arrayStringEnumDefaultItem) {
+    if (this.arrayStringEnumDefault == null) {
+      this.arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+    }
+    this.arrayStringEnumDefault.add(arrayStringEnumDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringEnumDefault
+   * @return arrayStringEnumDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<ArrayStringEnumDefaultEnum> getArrayStringEnumDefault() {
+    return arrayStringEnumDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+  }
+
+
+  public DefaultValue arrayStringDefault(List<String> arrayStringDefault) {
+    
+    this.arrayStringDefault = arrayStringDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringDefaultItem(String arrayStringDefaultItem) {
+    if (this.arrayStringDefault == null) {
+      this.arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+    }
+    this.arrayStringDefault.add(arrayStringDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringDefault
+   * @return arrayStringDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<String> getArrayStringDefault() {
+    return arrayStringDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayStringDefault(List<String> arrayStringDefault) {
+    this.arrayStringDefault = arrayStringDefault;
+  }
+
+
+  public DefaultValue arrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    
+    this.arrayIntegerDefault = arrayIntegerDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayIntegerDefaultItem(Integer arrayIntegerDefaultItem) {
+    if (this.arrayIntegerDefault == null) {
+      this.arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+    }
+    this.arrayIntegerDefault.add(arrayIntegerDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayIntegerDefault
+   * @return arrayIntegerDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_INTEGER_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<Integer> getArrayIntegerDefault() {
+    return arrayIntegerDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_INTEGER_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    this.arrayIntegerDefault = arrayIntegerDefault;
+  }
+
+
+  public DefaultValue arrayString(List<String> arrayString) {
+    
+    this.arrayString = arrayString;
+    return this;
+  }
+
+  public DefaultValue addArrayStringItem(String arrayStringItem) {
+    if (this.arrayString == null) {
+      this.arrayString = new ArrayList<>();
+    }
+    this.arrayString.add(arrayStringItem);
+    return this;
+  }
+
+   /**
+   * Get arrayString
+   * @return arrayString
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<String> getArrayString() {
+    return arrayString;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayString(List<String> arrayString) {
+    this.arrayString = arrayString;
+  }
+
+
+  public DefaultValue arrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = JsonNullable.<List<String>>of(arrayStringNullable);
+    
+    return this;
+  }
+
+  public DefaultValue addArrayStringNullableItem(String arrayStringNullableItem) {
+    if (this.arrayStringNullable == null || !this.arrayStringNullable.isPresent()) {
+      this.arrayStringNullable = JsonNullable.<List<String>>of(null);
+    }
+    try {
+      this.arrayStringNullable.get().add(arrayStringNullableItem);
+    } catch (java.util.NoSuchElementException e) {
+      // this can never happen, as we make sure above that the value is present
+    }
+    return this;
+  }
+
+   /**
+   * Get arrayStringNullable
+   * @return arrayStringNullable
+  **/
+  @javax.annotation.Nullable
+  @JsonIgnore
+
+  public List<String> getArrayStringNullable() {
+        return arrayStringNullable.orElse(null);
+  }
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_NULLABLE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public JsonNullable<List<String>> getArrayStringNullable_JsonNullable() {
+    return arrayStringNullable;
+  }
+  
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_NULLABLE)
+  public void setArrayStringNullable_JsonNullable(JsonNullable<List<String>> arrayStringNullable) {
+    this.arrayStringNullable = arrayStringNullable;
+  }
+
+  public void setArrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = JsonNullable.<List<String>>of(arrayStringNullable);
+  }
+
+
+  public DefaultValue stringNullable(String stringNullable) {
+    this.stringNullable = JsonNullable.<String>of(stringNullable);
+    
+    return this;
+  }
+
+   /**
+   * Get stringNullable
+   * @return stringNullable
+  **/
+  @javax.annotation.Nullable
+  @JsonIgnore
+
+  public String getStringNullable() {
+        return stringNullable.orElse(null);
+  }
+
+  @JsonProperty(JSON_PROPERTY_STRING_NULLABLE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public JsonNullable<String> getStringNullable_JsonNullable() {
+    return stringNullable;
+  }
+  
+  @JsonProperty(JSON_PROPERTY_STRING_NULLABLE)
+  public void setStringNullable_JsonNullable(JsonNullable<String> stringNullable) {
+    this.stringNullable = stringNullable;
+  }
+
+  public void setStringNullable(String stringNullable) {
+    this.stringNullable = JsonNullable.<String>of(stringNullable);
+  }
+
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    DefaultValue defaultValue = (DefaultValue) o;
+    return Objects.equals(this.arrayStringEnumDefault, defaultValue.arrayStringEnumDefault) &&
+        Objects.equals(this.arrayStringDefault, defaultValue.arrayStringDefault) &&
+        Objects.equals(this.arrayIntegerDefault, defaultValue.arrayIntegerDefault) &&
+        Objects.equals(this.arrayString, defaultValue.arrayString) &&
+        equalsNullable(this.arrayStringNullable, defaultValue.arrayStringNullable) &&
+        equalsNullable(this.stringNullable, defaultValue.stringNullable);
+  }
+
+  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
+    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(arrayStringEnumDefault, arrayStringDefault, arrayIntegerDefault, arrayString, hashCodeNullable(arrayStringNullable), hashCodeNullable(stringNullable));
+  }
+
+  private static <T> int hashCodeNullable(JsonNullable<T> a) {
+    if (a == null) {
+      return 1;
+    }
+    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class DefaultValue {\n");
+    sb.append("    arrayStringEnumDefault: ").append(toIndentedString(arrayStringEnumDefault)).append("\n");
+    sb.append("    arrayStringDefault: ").append(toIndentedString(arrayStringDefault)).append("\n");
+    sb.append("    arrayIntegerDefault: ").append(toIndentedString(arrayIntegerDefault)).append("\n");
+    sb.append("    arrayString: ").append(toIndentedString(arrayString)).append("\n");
+    sb.append("    arrayStringNullable: ").append(toIndentedString(arrayStringNullable)).append("\n");
+    sb.append("    stringNullable: ").append(toIndentedString(stringNullable)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+
+  /**
+   * Convert the instance into URL query string.
+   *
+   * @return URL query string
+   */
+  public String toUrlQueryString() {
+    return toUrlQueryString(null);
+  }
+
+  /**
+   * Convert the instance into URL query string.
+   *
+   * @param prefix prefix of the query string
+   * @return URL query string
+   */
+  public String toUrlQueryString(String prefix) {
+    String suffix = "";
+    String containerSuffix = "";
+    String containerPrefix = "";
+    if (prefix == null) {
+      // style=form, explode=true, e.g. /pet?name=cat&type=manx
+      prefix = "";
+    } else {
+      // deepObject style e.g. /pet?id[name]=cat&id[type]=manx
+      prefix = prefix + "[";
+      suffix = "]";
+      containerSuffix = "]";
+      containerPrefix = "[";
+    }
+
+    StringJoiner joiner = new StringJoiner("&");
+
+    // add `array_string_enum_default` to the URL query string
+    if (getArrayStringEnumDefault() != null) {
+      for (int i = 0; i < getArrayStringEnumDefault().size(); i++) {
+        try {
+          joiner.add(String.format("%sarray_string_enum_default%s%s=%s", prefix, suffix,
+              "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+              URLEncoder.encode(String.valueOf(getArrayStringEnumDefault().get(i)), "UTF-8").replaceAll("\\+", "%20")));
+        } catch (UnsupportedEncodingException e) {
+          // Should never happen, UTF-8 is always supported
+          throw new RuntimeException(e);
+        }
+      }
+    }
+
+    // add `array_string_default` to the URL query string
+    if (getArrayStringDefault() != null) {
+      for (int i = 0; i < getArrayStringDefault().size(); i++) {
+        try {
+          joiner.add(String.format("%sarray_string_default%s%s=%s", prefix, suffix,
+              "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+              URLEncoder.encode(String.valueOf(getArrayStringDefault().get(i)), "UTF-8").replaceAll("\\+", "%20")));
+        } catch (UnsupportedEncodingException e) {
+          // Should never happen, UTF-8 is always supported
+          throw new RuntimeException(e);
+        }
+      }
+    }
+
+    // add `array_integer_default` to the URL query string
+    if (getArrayIntegerDefault() != null) {
+      for (int i = 0; i < getArrayIntegerDefault().size(); i++) {
+        try {
+          joiner.add(String.format("%sarray_integer_default%s%s=%s", prefix, suffix,
+              "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+              URLEncoder.encode(String.valueOf(getArrayIntegerDefault().get(i)), "UTF-8").replaceAll("\\+", "%20")));
+        } catch (UnsupportedEncodingException e) {
+          // Should never happen, UTF-8 is always supported
+          throw new RuntimeException(e);
+        }
+      }
+    }
+
+    // add `array_string` to the URL query string
+    if (getArrayString() != null) {
+      for (int i = 0; i < getArrayString().size(); i++) {
+        try {
+          joiner.add(String.format("%sarray_string%s%s=%s", prefix, suffix,
+              "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+              URLEncoder.encode(String.valueOf(getArrayString().get(i)), "UTF-8").replaceAll("\\+", "%20")));
+        } catch (UnsupportedEncodingException e) {
+          // Should never happen, UTF-8 is always supported
+          throw new RuntimeException(e);
+        }
+      }
+    }
+
+    // add `array_string_nullable` to the URL query string
+    if (getArrayStringNullable() != null) {
+      for (int i = 0; i < getArrayStringNullable().size(); i++) {
+        try {
+          joiner.add(String.format("%sarray_string_nullable%s%s=%s", prefix, suffix,
+              "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+              URLEncoder.encode(String.valueOf(getArrayStringNullable().get(i)), "UTF-8").replaceAll("\\+", "%20")));
+        } catch (UnsupportedEncodingException e) {
+          // Should never happen, UTF-8 is always supported
+          throw new RuntimeException(e);
+        }
+      }
+    }
+
+    // add `string_nullable` to the URL query string
+    if (getStringNullable() != null) {
+      try {
+        joiner.add(String.format("%sstring_nullable%s=%s", prefix, suffix, URLEncoder.encode(String.valueOf(getStringNullable()), "UTF-8").replaceAll("\\+", "%20")));
+      } catch (UnsupportedEncodingException e) {
+        // Should never happen, UTF-8 is always supported
+        throw new RuntimeException(e);
+      }
+    }
+
+    return joiner.toString();
+  }
+
+}
+

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Pet.java

@@ -56,7 +56,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags = null;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/Query.java

@@ -78,7 +78,7 @@ public class Query {
   }
 
   public static final String JSON_PROPERTY_OUTCOMES = "outcomes";
-  private List<OutcomesEnum> outcomes = null;
+  private List<OutcomesEnum> outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
 
   public Query() {
   }
@@ -117,7 +117,7 @@ public class Query {
 
   public Query addOutcomesItem(OutcomesEnum outcomesItem) {
     if (this.outcomes == null) {
-      this.outcomes = new ArrayList<>();
+      this.outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
     }
     this.outcomes.add(outcomesItem);
     return this;

samples/client/echo_api/java/apache-httpclient/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java

@@ -38,7 +38,7 @@ import java.util.StringJoiner;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String JSON_PROPERTY_VALUES = "values";
-  private List<String> values = null;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }

samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/CustomTest.java

@@ -13,6 +13,7 @@
 
 package org.openapitools.client;
 
+import com.fasterxml.jackson.core.type.TypeReference;
 import org.junit.Assert;
 import org.openapitools.client.ApiException;
 import org.openapitools.client.api.*;
@@ -20,6 +21,7 @@ import org.openapitools.client.model.*;
 import org.junit.Test;
 import org.junit.Ignore;
 
+import java.io.IOException;
 import java.util.*;
 
 
@@ -138,4 +140,106 @@ public class CustomTest {
         Assert.assertEquals("/query/integer/boolean/string?integer_query=1&boolean_query=true&string_query=Hello%20World", p.path);
     }
 
+    @Test
+    public void testArrayDefaultValues() {
+        // test array default values
+        DefaultValue d = new DefaultValue();
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        // test addItem
+        d.addArrayStringEnumDefaultItem(DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 3);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(2), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+
+        d.addArrayStringDefaultItem("new item");
+        Assert.assertEquals(d.getArrayStringDefault().size(), 3);
+        Assert.assertEquals(d.getArrayStringDefault().get(2), "new item");
+
+        d.addArrayIntegerDefaultItem(5);
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 3);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(2), Integer.valueOf(5));
+
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{}";
+
+        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+        });
+
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3],\"array_string\":[],\"array_string_nullable\":{\"present\":false},\"string_nullable\":{\"present\":false}}");
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithJSONString() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{ \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
+
+        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+        });
+
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 1);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 1);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3],\"array_string\":[],\"array_string_nullable\":{\"present\":false},\"string_nullable\":{\"present\":false}}");
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
+
+        try {
+            DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+            });
+            Assert.assertTrue(false); // the test should not reach this line
+        } catch (com.fasterxml.jackson.databind.exc.ValueInstantiationException e) {
+            Assert.assertEquals(e.getMessage(), "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
+                    " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])");
+        }
+    }
+
 }

samples/client/echo_api/java/apache-httpclient/src/test/java/org/openapitools/client/model/DefaultValueTest.java

@@ -0,0 +1,94 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import com.fasterxml.jackson.annotation.JsonValue;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import org.openapitools.jackson.nullable.JsonNullable;
+import java.util.NoSuchElementException;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+
+/**
+ * Model tests for DefaultValue
+ */
+public class DefaultValueTest {
+    private final DefaultValue model = new DefaultValue();
+
+    /**
+     * Model tests for DefaultValue
+     */
+    @Test
+    public void testDefaultValue() {
+        // TODO: test DefaultValue
+    }
+
+    /**
+     * Test the property 'arrayStringEnumDefault'
+     */
+    @Test
+    public void arrayStringEnumDefaultTest() {
+        // TODO: test arrayStringEnumDefault
+    }
+
+    /**
+     * Test the property 'arrayStringDefault'
+     */
+    @Test
+    public void arrayStringDefaultTest() {
+        // TODO: test arrayStringDefault
+    }
+
+    /**
+     * Test the property 'arrayIntegerDefault'
+     */
+    @Test
+    public void arrayIntegerDefaultTest() {
+        // TODO: test arrayIntegerDefault
+    }
+
+    /**
+     * Test the property 'arrayString'
+     */
+    @Test
+    public void arrayStringTest() {
+        // TODO: test arrayString
+    }
+
+    /**
+     * Test the property 'arrayStringNullable'
+     */
+    @Test
+    public void arrayStringNullableTest() {
+        // TODO: test arrayStringNullable
+    }
+
+    /**
+     * Test the property 'stringNullable'
+     */
+    @Test
+    public void stringNullableTest() {
+        // TODO: test stringNullable
+    }
+
+}

samples/client/echo_api/java/feign-gson/.openapi-generator/FILES

@@ -30,6 +30,7 @@ src/main/java/org/openapitools/client/model/Bird.java
 src/main/java/org/openapitools/client/model/Category.java
 src/main/java/org/openapitools/client/model/DataQuery.java
 src/main/java/org/openapitools/client/model/DataQueryAllOf.java
+src/main/java/org/openapitools/client/model/DefaultValue.java
 src/main/java/org/openapitools/client/model/Pet.java
 src/main/java/org/openapitools/client/model/Query.java
 src/main/java/org/openapitools/client/model/Tag.java

samples/client/echo_api/java/feign-gson/api/openapi.yaml

@@ -301,6 +301,47 @@ components:
       type: object
       xml:
         name: pet
+    DefaultValue:
+      description: to test the default value of properties
+      properties:
+        array_string_enum_default:
+          default:
+          - success
+          - failure
+          items:
+            enum:
+            - success
+            - failure
+            - unclassified
+            type: string
+          type: array
+        array_string_default:
+          default:
+          - failure
+          - skipped
+          items:
+            type: string
+          type: array
+        array_integer_default:
+          default:
+          - 1
+          - 3
+          items:
+            type: integer
+          type: array
+        array_string:
+          items:
+            type: string
+          type: array
+        array_string_nullable:
+          items:
+            type: string
+          nullable: true
+          type: array
+        string_nullable:
+          nullable: true
+          type: string
+      type: object
     Bird:
       properties:
         size:

samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/DefaultValue.java

@@ -0,0 +1,340 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import java.util.Objects;
+import java.util.Arrays;
+import com.google.gson.TypeAdapter;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+
+/**
+ * to test the default value of properties
+ */
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class DefaultValue {
+  /**
+   * Gets or Sets arrayStringEnumDefault
+   */
+  @JsonAdapter(ArrayStringEnumDefaultEnum.Adapter.class)
+  public enum ArrayStringEnumDefaultEnum {
+    SUCCESS("success"),
+    
+    FAILURE("failure"),
+    
+    UNCLASSIFIED("unclassified");
+
+    private String value;
+
+    ArrayStringEnumDefaultEnum(String value) {
+      this.value = value;
+    }
+
+    public String getValue() {
+      return value;
+    }
+
+    @Override
+    public String toString() {
+      return String.valueOf(value);
+    }
+
+    public static ArrayStringEnumDefaultEnum fromValue(String value) {
+      for (ArrayStringEnumDefaultEnum b : ArrayStringEnumDefaultEnum.values()) {
+        if (b.value.equals(value)) {
+          return b;
+        }
+      }
+      throw new IllegalArgumentException("Unexpected value '" + value + "'");
+    }
+
+    public static class Adapter extends TypeAdapter<ArrayStringEnumDefaultEnum> {
+      @Override
+      public void write(final JsonWriter jsonWriter, final ArrayStringEnumDefaultEnum enumeration) throws IOException {
+        jsonWriter.value(enumeration.getValue());
+      }
+
+      @Override
+      public ArrayStringEnumDefaultEnum read(final JsonReader jsonReader) throws IOException {
+        String value =  jsonReader.nextString();
+        return ArrayStringEnumDefaultEnum.fromValue(value);
+      }
+    }
+  }
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_ENUM_DEFAULT = "array_string_enum_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_ENUM_DEFAULT)
+  private List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_DEFAULT = "array_string_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_DEFAULT)
+  private List<String> arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+
+  public static final String SERIALIZED_NAME_ARRAY_INTEGER_DEFAULT = "array_integer_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_INTEGER_DEFAULT)
+  private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING = "array_string";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING)
+  private List<String> arrayString = new ArrayList<>();
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_NULLABLE = "array_string_nullable";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_NULLABLE)
+  private List<String> arrayStringNullable = null;
+
+  public static final String SERIALIZED_NAME_STRING_NULLABLE = "string_nullable";
+  @SerializedName(SERIALIZED_NAME_STRING_NULLABLE)
+  private String stringNullable;
+
+  public DefaultValue() {
+  }
+
+  public DefaultValue arrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringEnumDefaultItem(ArrayStringEnumDefaultEnum arrayStringEnumDefaultItem) {
+    if (this.arrayStringEnumDefault == null) {
+      this.arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+    }
+    this.arrayStringEnumDefault.add(arrayStringEnumDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringEnumDefault
+   * @return arrayStringEnumDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<ArrayStringEnumDefaultEnum> getArrayStringEnumDefault() {
+    return arrayStringEnumDefault;
+  }
+
+
+  public void setArrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+  }
+
+
+  public DefaultValue arrayStringDefault(List<String> arrayStringDefault) {
+    
+    this.arrayStringDefault = arrayStringDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringDefaultItem(String arrayStringDefaultItem) {
+    if (this.arrayStringDefault == null) {
+      this.arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+    }
+    this.arrayStringDefault.add(arrayStringDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringDefault
+   * @return arrayStringDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayStringDefault() {
+    return arrayStringDefault;
+  }
+
+
+  public void setArrayStringDefault(List<String> arrayStringDefault) {
+    this.arrayStringDefault = arrayStringDefault;
+  }
+
+
+  public DefaultValue arrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    
+    this.arrayIntegerDefault = arrayIntegerDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayIntegerDefaultItem(Integer arrayIntegerDefaultItem) {
+    if (this.arrayIntegerDefault == null) {
+      this.arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+    }
+    this.arrayIntegerDefault.add(arrayIntegerDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayIntegerDefault
+   * @return arrayIntegerDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<Integer> getArrayIntegerDefault() {
+    return arrayIntegerDefault;
+  }
+
+
+  public void setArrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    this.arrayIntegerDefault = arrayIntegerDefault;
+  }
+
+
+  public DefaultValue arrayString(List<String> arrayString) {
+    
+    this.arrayString = arrayString;
+    return this;
+  }
+
+  public DefaultValue addArrayStringItem(String arrayStringItem) {
+    if (this.arrayString == null) {
+      this.arrayString = new ArrayList<>();
+    }
+    this.arrayString.add(arrayStringItem);
+    return this;
+  }
+
+   /**
+   * Get arrayString
+   * @return arrayString
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayString() {
+    return arrayString;
+  }
+
+
+  public void setArrayString(List<String> arrayString) {
+    this.arrayString = arrayString;
+  }
+
+
+  public DefaultValue arrayStringNullable(List<String> arrayStringNullable) {
+    
+    this.arrayStringNullable = arrayStringNullable;
+    return this;
+  }
+
+  public DefaultValue addArrayStringNullableItem(String arrayStringNullableItem) {
+    if (this.arrayStringNullable == null) {
+      this.arrayStringNullable = null;
+    }
+    this.arrayStringNullable.add(arrayStringNullableItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringNullable
+   * @return arrayStringNullable
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayStringNullable() {
+    return arrayStringNullable;
+  }
+
+
+  public void setArrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = arrayStringNullable;
+  }
+
+
+  public DefaultValue stringNullable(String stringNullable) {
+    
+    this.stringNullable = stringNullable;
+    return this;
+  }
+
+   /**
+   * Get stringNullable
+   * @return stringNullable
+  **/
+  @javax.annotation.Nullable
+
+  public String getStringNullable() {
+    return stringNullable;
+  }
+
+
+  public void setStringNullable(String stringNullable) {
+    this.stringNullable = stringNullable;
+  }
+
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    DefaultValue defaultValue = (DefaultValue) o;
+    return Objects.equals(this.arrayStringEnumDefault, defaultValue.arrayStringEnumDefault) &&
+        Objects.equals(this.arrayStringDefault, defaultValue.arrayStringDefault) &&
+        Objects.equals(this.arrayIntegerDefault, defaultValue.arrayIntegerDefault) &&
+        Objects.equals(this.arrayString, defaultValue.arrayString) &&
+        Objects.equals(this.arrayStringNullable, defaultValue.arrayStringNullable) &&
+        Objects.equals(this.stringNullable, defaultValue.stringNullable);
+  }
+
+  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
+    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(arrayStringEnumDefault, arrayStringDefault, arrayIntegerDefault, arrayString, arrayStringNullable, stringNullable);
+  }
+
+  private static <T> int hashCodeNullable(JsonNullable<T> a) {
+    if (a == null) {
+      return 1;
+    }
+    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class DefaultValue {\n");
+    sb.append("    arrayStringEnumDefault: ").append(toIndentedString(arrayStringEnumDefault)).append("\n");
+    sb.append("    arrayStringDefault: ").append(toIndentedString(arrayStringDefault)).append("\n");
+    sb.append("    arrayIntegerDefault: ").append(toIndentedString(arrayIntegerDefault)).append("\n");
+    sb.append("    arrayString: ").append(toIndentedString(arrayString)).append("\n");
+    sb.append("    arrayStringNullable: ").append(toIndentedString(arrayStringNullable)).append("\n");
+    sb.append("    stringNullable: ").append(toIndentedString(stringNullable)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+
+}
+

samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Pet.java

@@ -49,7 +49,7 @@ public class Pet {
 
   public static final String SERIALIZED_NAME_TAGS = "tags";
   @SerializedName(SERIALIZED_NAME_TAGS)
-  private List<Tag> tags = null;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store

samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/Query.java

@@ -84,7 +84,7 @@ public class Query {
 
   public static final String SERIALIZED_NAME_OUTCOMES = "outcomes";
   @SerializedName(SERIALIZED_NAME_OUTCOMES)
-  private List<OutcomesEnum> outcomes = null;
+  private List<OutcomesEnum> outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
 
   public Query() {
   }
@@ -119,7 +119,7 @@ public class Query {
 
   public Query addOutcomesItem(OutcomesEnum outcomesItem) {
     if (this.outcomes == null) {
-      this.outcomes = new ArrayList<>();
+      this.outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
     }
     this.outcomes.add(outcomesItem);
     return this;

samples/client/echo_api/java/feign-gson/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java

@@ -31,7 +31,7 @@ import java.util.List;
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String SERIALIZED_NAME_VALUES = "values";
   @SerializedName(SERIALIZED_NAME_VALUES)
-  private List<String> values = null;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() {
   }

samples/client/echo_api/java/feign-gson/src/test/java/org/openapitools/client/model/DefaultValueTest.java

@@ -0,0 +1,90 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import com.google.gson.TypeAdapter;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import org.junit.jupiter.api.Test;
+
+
+/**
+ * Model tests for DefaultValue
+ */
+class DefaultValueTest {
+    private final DefaultValue model = new DefaultValue();
+
+    /**
+     * Model tests for DefaultValue
+     */
+    @Test
+    void testDefaultValue() {
+        // TODO: test DefaultValue
+    }
+
+    /**
+     * Test the property 'arrayStringEnumDefault'
+     */
+    @Test
+    void arrayStringEnumDefaultTest() {
+        // TODO: test arrayStringEnumDefault
+    }
+
+    /**
+     * Test the property 'arrayStringDefault'
+     */
+    @Test
+    void arrayStringDefaultTest() {
+        // TODO: test arrayStringDefault
+    }
+
+    /**
+     * Test the property 'arrayIntegerDefault'
+     */
+    @Test
+    void arrayIntegerDefaultTest() {
+        // TODO: test arrayIntegerDefault
+    }
+
+    /**
+     * Test the property 'arrayString'
+     */
+    @Test
+    void arrayStringTest() {
+        // TODO: test arrayString
+    }
+
+    /**
+     * Test the property 'arrayStringNullable'
+     */
+    @Test
+    void arrayStringNullableTest() {
+        // TODO: test arrayStringNullable
+    }
+
+    /**
+     * Test the property 'stringNullable'
+     */
+    @Test
+    void stringNullableTest() {
+        // TODO: test stringNullable
+    }
+
+}

samples/client/echo_api/java/native/.openapi-generator/FILES

@@ -10,6 +10,7 @@ docs/BodyApi.md
 docs/Category.md
 docs/DataQuery.md
 docs/DataQueryAllOf.md
+docs/DefaultValue.md
 docs/PathApi.md
 docs/Pet.md
 docs/Query.md
@@ -43,6 +44,7 @@ src/main/java/org/openapitools/client/model/Bird.java
 src/main/java/org/openapitools/client/model/Category.java
 src/main/java/org/openapitools/client/model/DataQuery.java
 src/main/java/org/openapitools/client/model/DataQueryAllOf.java
+src/main/java/org/openapitools/client/model/DefaultValue.java
 src/main/java/org/openapitools/client/model/Pet.java
 src/main/java/org/openapitools/client/model/Query.java
 src/main/java/org/openapitools/client/model/Tag.java

samples/client/echo_api/java/native/README.md

@@ -129,6 +129,7 @@ Class | Method | HTTP request | Description
  - [Category](docs/Category.md)
  - [DataQuery](docs/DataQuery.md)
  - [DataQueryAllOf](docs/DataQueryAllOf.md)
+ - [DefaultValue](docs/DefaultValue.md)
  - [Pet](docs/Pet.md)
  - [Query](docs/Query.md)
  - [Tag](docs/Tag.md)

samples/client/echo_api/java/native/api/openapi.yaml

@@ -301,6 +301,47 @@ components:
       type: object
       xml:
         name: pet
+    DefaultValue:
+      description: to test the default value of properties
+      properties:
+        array_string_enum_default:
+          default:
+          - success
+          - failure
+          items:
+            enum:
+            - success
+            - failure
+            - unclassified
+            type: string
+          type: array
+        array_string_default:
+          default:
+          - failure
+          - skipped
+          items:
+            type: string
+          type: array
+        array_integer_default:
+          default:
+          - 1
+          - 3
+          items:
+            type: integer
+          type: array
+        array_string:
+          items:
+            type: string
+          type: array
+        array_string_nullable:
+          items:
+            type: string
+          nullable: true
+          type: array
+        string_nullable:
+          nullable: true
+          type: string
+      type: object
     Bird:
       properties:
         size:

samples/client/echo_api/java/native/docs/DefaultValue.md

@@ -0,0 +1,29 @@
+
+
+# DefaultValue
+
+to test the default value of properties
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**arrayStringEnumDefault** | [**List<ArrayStringEnumDefaultEnum>**](#List<ArrayStringEnumDefaultEnum>) |  |  [optional] |
+|**arrayStringDefault** | **List<String>** |  |  [optional] |
+|**arrayIntegerDefault** | **List<Integer>** |  |  [optional] |
+|**arrayString** | **List<String>** |  |  [optional] |
+|**arrayStringNullable** | **List<String>** |  |  [optional] |
+|**stringNullable** | **String** |  |  [optional] |
+
+
+
+## Enum: List<ArrayStringEnumDefaultEnum>
+
+| Name | Value |
+|---- | -----|
+| SUCCESS | "success" |
+| FAILURE | "failure" |
+| UNCLASSIFIED | "unclassified" |
+
+
+

samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/DefaultValue.java

@@ -0,0 +1,464 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
+import java.util.StringJoiner;
+import java.util.Objects;
+import java.util.Arrays;
+import java.util.Map;
+import java.util.HashMap;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import com.fasterxml.jackson.annotation.JsonValue;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import org.openapitools.jackson.nullable.JsonNullable;
+import java.util.NoSuchElementException;
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+
+
+/**
+ * to test the default value of properties
+ */
+@JsonPropertyOrder({
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_INTEGER_DEFAULT,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING,
+  DefaultValue.JSON_PROPERTY_ARRAY_STRING_NULLABLE,
+  DefaultValue.JSON_PROPERTY_STRING_NULLABLE
+})
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class DefaultValue {
+  /**
+   * Gets or Sets arrayStringEnumDefault
+   */
+  public enum ArrayStringEnumDefaultEnum {
+    SUCCESS("success"),
+    
+    FAILURE("failure"),
+    
+    UNCLASSIFIED("unclassified");
+
+    private String value;
+
+    ArrayStringEnumDefaultEnum(String value) {
+      this.value = value;
+    }
+
+    @JsonValue
+    public String getValue() {
+      return value;
+    }
+
+    @Override
+    public String toString() {
+      return String.valueOf(value);
+    }
+
+    @JsonCreator
+    public static ArrayStringEnumDefaultEnum fromValue(String value) {
+      for (ArrayStringEnumDefaultEnum b : ArrayStringEnumDefaultEnum.values()) {
+        if (b.value.equals(value)) {
+          return b;
+        }
+      }
+      throw new IllegalArgumentException("Unexpected value '" + value + "'");
+    }
+  }
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT = "array_string_enum_default";
+  private List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_DEFAULT = "array_string_default";
+  private List<String> arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+
+  public static final String JSON_PROPERTY_ARRAY_INTEGER_DEFAULT = "array_integer_default";
+  private List<Integer> arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+
+  public static final String JSON_PROPERTY_ARRAY_STRING = "array_string";
+  private List<String> arrayString = new ArrayList<>();
+
+  public static final String JSON_PROPERTY_ARRAY_STRING_NULLABLE = "array_string_nullable";
+  private JsonNullable<List<String>> arrayStringNullable = JsonNullable.<List<String>>undefined();
+
+  public static final String JSON_PROPERTY_STRING_NULLABLE = "string_nullable";
+  private JsonNullable<String> stringNullable = JsonNullable.<String>undefined();
+
+  public DefaultValue() { 
+  }
+
+  public DefaultValue arrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringEnumDefaultItem(ArrayStringEnumDefaultEnum arrayStringEnumDefaultItem) {
+    if (this.arrayStringEnumDefault == null) {
+      this.arrayStringEnumDefault = new ArrayList<>();
+    }
+    this.arrayStringEnumDefault.add(arrayStringEnumDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringEnumDefault
+   * @return arrayStringEnumDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<ArrayStringEnumDefaultEnum> getArrayStringEnumDefault() {
+    return arrayStringEnumDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_ENUM_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+  }
+
+
+  public DefaultValue arrayStringDefault(List<String> arrayStringDefault) {
+    this.arrayStringDefault = arrayStringDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringDefaultItem(String arrayStringDefaultItem) {
+    if (this.arrayStringDefault == null) {
+      this.arrayStringDefault = new ArrayList<>();
+    }
+    this.arrayStringDefault.add(arrayStringDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringDefault
+   * @return arrayStringDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<String> getArrayStringDefault() {
+    return arrayStringDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayStringDefault(List<String> arrayStringDefault) {
+    this.arrayStringDefault = arrayStringDefault;
+  }
+
+
+  public DefaultValue arrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    this.arrayIntegerDefault = arrayIntegerDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayIntegerDefaultItem(Integer arrayIntegerDefaultItem) {
+    if (this.arrayIntegerDefault == null) {
+      this.arrayIntegerDefault = new ArrayList<>();
+    }
+    this.arrayIntegerDefault.add(arrayIntegerDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayIntegerDefault
+   * @return arrayIntegerDefault
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_INTEGER_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<Integer> getArrayIntegerDefault() {
+    return arrayIntegerDefault;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_INTEGER_DEFAULT)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    this.arrayIntegerDefault = arrayIntegerDefault;
+  }
+
+
+  public DefaultValue arrayString(List<String> arrayString) {
+    this.arrayString = arrayString;
+    return this;
+  }
+
+  public DefaultValue addArrayStringItem(String arrayStringItem) {
+    if (this.arrayString == null) {
+      this.arrayString = new ArrayList<>();
+    }
+    this.arrayString.add(arrayStringItem);
+    return this;
+  }
+
+   /**
+   * Get arrayString
+   * @return arrayString
+  **/
+  @javax.annotation.Nullable
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public List<String> getArrayString() {
+    return arrayString;
+  }
+
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+  public void setArrayString(List<String> arrayString) {
+    this.arrayString = arrayString;
+  }
+
+
+  public DefaultValue arrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = JsonNullable.<List<String>>of(arrayStringNullable);
+    return this;
+  }
+
+  public DefaultValue addArrayStringNullableItem(String arrayStringNullableItem) {
+    if (this.arrayStringNullable == null || !this.arrayStringNullable.isPresent()) {
+      this.arrayStringNullable = JsonNullable.<List<String>>of(null);
+    }
+    try {
+      this.arrayStringNullable.get().add(arrayStringNullableItem);
+    } catch (java.util.NoSuchElementException e) {
+      // this can never happen, as we make sure above that the value is present
+    }
+    return this;
+  }
+
+   /**
+   * Get arrayStringNullable
+   * @return arrayStringNullable
+  **/
+  @javax.annotation.Nullable
+  @JsonIgnore
+
+  public List<String> getArrayStringNullable() {
+        return arrayStringNullable.orElse(null);
+  }
+
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_NULLABLE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public JsonNullable<List<String>> getArrayStringNullable_JsonNullable() {
+    return arrayStringNullable;
+  }
+  
+  @JsonProperty(JSON_PROPERTY_ARRAY_STRING_NULLABLE)
+  public void setArrayStringNullable_JsonNullable(JsonNullable<List<String>> arrayStringNullable) {
+    this.arrayStringNullable = arrayStringNullable;
+  }
+
+  public void setArrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = JsonNullable.<List<String>>of(arrayStringNullable);
+  }
+
+
+  public DefaultValue stringNullable(String stringNullable) {
+    this.stringNullable = JsonNullable.<String>of(stringNullable);
+    return this;
+  }
+
+   /**
+   * Get stringNullable
+   * @return stringNullable
+  **/
+  @javax.annotation.Nullable
+  @JsonIgnore
+
+  public String getStringNullable() {
+        return stringNullable.orElse(null);
+  }
+
+  @JsonProperty(JSON_PROPERTY_STRING_NULLABLE)
+  @JsonInclude(value = JsonInclude.Include.USE_DEFAULTS)
+
+  public JsonNullable<String> getStringNullable_JsonNullable() {
+    return stringNullable;
+  }
+  
+  @JsonProperty(JSON_PROPERTY_STRING_NULLABLE)
+  public void setStringNullable_JsonNullable(JsonNullable<String> stringNullable) {
+    this.stringNullable = stringNullable;
+  }
+
+  public void setStringNullable(String stringNullable) {
+    this.stringNullable = JsonNullable.<String>of(stringNullable);
+  }
+
+
+  /**
+   * Return true if this DefaultValue object is equal to o.
+   */
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    DefaultValue defaultValue = (DefaultValue) o;
+    return Objects.equals(this.arrayStringEnumDefault, defaultValue.arrayStringEnumDefault) &&
+        Objects.equals(this.arrayStringDefault, defaultValue.arrayStringDefault) &&
+        Objects.equals(this.arrayIntegerDefault, defaultValue.arrayIntegerDefault) &&
+        Objects.equals(this.arrayString, defaultValue.arrayString) &&
+        equalsNullable(this.arrayStringNullable, defaultValue.arrayStringNullable) &&
+        equalsNullable(this.stringNullable, defaultValue.stringNullable);
+  }
+
+  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
+    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(arrayStringEnumDefault, arrayStringDefault, arrayIntegerDefault, arrayString, hashCodeNullable(arrayStringNullable), hashCodeNullable(stringNullable));
+  }
+
+  private static <T> int hashCodeNullable(JsonNullable<T> a) {
+    if (a == null) {
+      return 1;
+    }
+    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class DefaultValue {\n");
+    sb.append("    arrayStringEnumDefault: ").append(toIndentedString(arrayStringEnumDefault)).append("\n");
+    sb.append("    arrayStringDefault: ").append(toIndentedString(arrayStringDefault)).append("\n");
+    sb.append("    arrayIntegerDefault: ").append(toIndentedString(arrayIntegerDefault)).append("\n");
+    sb.append("    arrayString: ").append(toIndentedString(arrayString)).append("\n");
+    sb.append("    arrayStringNullable: ").append(toIndentedString(arrayStringNullable)).append("\n");
+    sb.append("    stringNullable: ").append(toIndentedString(stringNullable)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+
+  /**
+   * Convert the instance into URL query string.
+   *
+   * @return URL query string
+   */
+  public String toUrlQueryString() {
+    return toUrlQueryString(null);
+  }
+
+  /**
+   * Convert the instance into URL query string.
+   *
+   * @param prefix prefix of the query string
+   * @return URL query string
+   */
+  public String toUrlQueryString(String prefix) {
+    String suffix = "";
+    String containerSuffix = "";
+    String containerPrefix = "";
+    if (prefix == null) {
+      // style=form, explode=true, e.g. /pet?name=cat&type=manx
+      prefix = "";
+    } else {
+      // deepObject style e.g. /pet?id[name]=cat&id[type]=manx
+      prefix = prefix + "[";
+      suffix = "]";
+      containerSuffix = "]";
+      containerPrefix = "[";
+    }
+
+    StringJoiner joiner = new StringJoiner("&");
+
+    // add `array_string_enum_default` to the URL query string
+    if (getArrayStringEnumDefault() != null) {
+      for (int i = 0; i < getArrayStringEnumDefault().size(); i++) {
+        joiner.add(String.format("%sarray_string_enum_default%s%s=%s", prefix, suffix,
+            "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+            URLEncoder.encode(String.valueOf(getArrayStringEnumDefault().get(i)), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+      }
+    }
+
+    // add `array_string_default` to the URL query string
+    if (getArrayStringDefault() != null) {
+      for (int i = 0; i < getArrayStringDefault().size(); i++) {
+        joiner.add(String.format("%sarray_string_default%s%s=%s", prefix, suffix,
+            "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+            URLEncoder.encode(String.valueOf(getArrayStringDefault().get(i)), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+      }
+    }
+
+    // add `array_integer_default` to the URL query string
+    if (getArrayIntegerDefault() != null) {
+      for (int i = 0; i < getArrayIntegerDefault().size(); i++) {
+        joiner.add(String.format("%sarray_integer_default%s%s=%s", prefix, suffix,
+            "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+            URLEncoder.encode(String.valueOf(getArrayIntegerDefault().get(i)), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+      }
+    }
+
+    // add `array_string` to the URL query string
+    if (getArrayString() != null) {
+      for (int i = 0; i < getArrayString().size(); i++) {
+        joiner.add(String.format("%sarray_string%s%s=%s", prefix, suffix,
+            "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+            URLEncoder.encode(String.valueOf(getArrayString().get(i)), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+      }
+    }
+
+    // add `array_string_nullable` to the URL query string
+    if (getArrayStringNullable() != null) {
+      for (int i = 0; i < getArrayStringNullable().size(); i++) {
+        joiner.add(String.format("%sarray_string_nullable%s%s=%s", prefix, suffix,
+            "".equals(suffix) ? "" : String.format("%s%d%s", containerPrefix, i, containerSuffix),
+            URLEncoder.encode(String.valueOf(getArrayStringNullable().get(i)), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+      }
+    }
+
+    // add `string_nullable` to the URL query string
+    if (getStringNullable() != null) {
+      joiner.add(String.format("%sstring_nullable%s=%s", prefix, suffix, URLEncoder.encode(String.valueOf(getStringNullable()), StandardCharsets.UTF_8).replaceAll("\\+", "%20")));
+    }
+
+    return joiner.toString();
+  }
+}
+

samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Pet.java

@@ -58,7 +58,7 @@ public class Pet {
   private List<String> photoUrls = new ArrayList<>();
 
   public static final String JSON_PROPERTY_TAGS = "tags";
-  private List<Tag> tags = null;
+  private List<Tag> tags = new ArrayList<>();
 
   /**
    * pet status in the store

samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/Query.java

@@ -80,7 +80,7 @@ public class Query {
   }
 
   public static final String JSON_PROPERTY_OUTCOMES = "outcomes";
-  private List<OutcomesEnum> outcomes = null;
+  private List<OutcomesEnum> outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
 
   public Query() { 
   }

samples/client/echo_api/java/native/src/main/java/org/openapitools/client/model/TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter.java

@@ -39,7 +39,7 @@ import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 @javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
 public class TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter {
   public static final String JSON_PROPERTY_VALUES = "values";
-  private List<String> values = null;
+  private List<String> values = new ArrayList<>();
 
   public TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter() { 
   }

samples/client/echo_api/java/native/src/test/java/org/openapitools/client/CustomTest.java

@@ -13,6 +13,7 @@
 
 package org.openapitools.client;
 
+import com.fasterxml.jackson.core.type.TypeReference;
 import org.junit.Assert;
 import org.openapitools.client.ApiException;
 import org.openapitools.client.api.*;
@@ -20,9 +21,9 @@ import org.openapitools.client.model.*;
 import org.junit.Test;
 import org.junit.Ignore;
 
+import java.io.IOException;
 import java.util.*;
 
-
 /**
  * API tests for QueryApi
  */
@@ -143,4 +144,105 @@ public class CustomTest {
         org.openapitools.client.EchoServerResponseParser p = new org.openapitools.client.EchoServerResponseParser(response);
         Assert.assertEquals("/query/style_form/explode_true/array_string?values=hello%20world%201&values=hello%20world%202", p.path);
     }
+
+    @Test
+    public void testArrayDefaultValues() {
+        // test array default values
+        DefaultValue d = new DefaultValue();
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        // test addItem
+        d.addArrayStringEnumDefaultItem(DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 3);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(2), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+
+        d.addArrayStringDefaultItem("new item");
+        Assert.assertEquals(d.getArrayStringDefault().size(), 3);
+        Assert.assertEquals(d.getArrayStringDefault().get(2), "new item");
+
+        d.addArrayIntegerDefaultItem(5);
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 3);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(2), Integer.valueOf(5));
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithEmptyPayload() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{}";
+
+        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+        });
+
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.SUCCESS);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(1), DefaultValue.ArrayStringEnumDefaultEnum.FAILURE);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 2);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+        Assert.assertEquals(d.getArrayStringDefault().get(1), "skipped");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_default\":[\"success\",\"failure\"],\"array_string_default\":[\"failure\",\"skipped\"],\"array_integer_default\":[1,3],\"array_string\":[]}");
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithJSONString() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{ \"array_string_enum_default\": [\"unclassified\"], \"array_string_default\": [\"failure\"] }";
+
+        DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+        });
+
+        Assert.assertEquals(d.getArrayStringEnumDefault().size(), 1);
+        Assert.assertEquals(d.getArrayStringEnumDefault().get(0), DefaultValue.ArrayStringEnumDefaultEnum.UNCLASSIFIED);
+
+        Assert.assertEquals(d.getArrayStringDefault().size(), 1);
+        Assert.assertEquals(d.getArrayStringDefault().get(0), "failure");
+
+        Assert.assertEquals(d.getArrayIntegerDefault().size(), 2);
+        Assert.assertEquals(d.getArrayIntegerDefault().get(0), Integer.valueOf(1));
+        Assert.assertEquals(d.getArrayIntegerDefault().get(1), Integer.valueOf(3));
+
+        Assert.assertNull(d.getArrayStringNullable());
+        Assert.assertEquals(d.getArrayString().size(), 0);
+
+        Assert.assertEquals(apiClient.getObjectMapper().writeValueAsString(d), "{\"array_string_enum_default\":[\"unclassified\"],\"array_string_default\":[\"failure\"],\"array_integer_default\":[1,3],\"array_string\":[]}");
+    }
+
+    @Test
+    public void testDefaultValuesSerializationWithIncorrectDefaultValues() throws IOException {
+        ApiClient apiClient = new ApiClient();
+
+        String str = "{ \"array_string_enum_default\": [\"invalid\"] }";
+
+        try {
+            DefaultValue d = apiClient.getObjectMapper().readValue(str, new TypeReference<DefaultValue>() {
+            });
+            Assert.assertTrue(false); // the test should not reach this line
+        } catch (com.fasterxml.jackson.databind.exc.ValueInstantiationException e) {
+            Assert.assertEquals(e.getMessage(), "Cannot construct instance of `org.openapitools.client.model.DefaultValue$ArrayStringEnumDefaultEnum`, problem: Unexpected value 'invalid'\n" +
+                    " at [Source: (String)\"{ \"array_string_enum_default\": [\"invalid\"] }\"; line: 1, column: 33] (through reference chain: org.openapitools.client.model.DefaultValue[\"array_string_enum_default\"]->java.util.ArrayList[0])");
+        }
+    }
 }

samples/client/echo_api/java/native/src/test/java/org/openapitools/client/model/DefaultValueTest.java

@@ -0,0 +1,86 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonCreator;
+import com.fasterxml.jackson.annotation.JsonTypeName;
+import com.fasterxml.jackson.annotation.JsonValue;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import org.openapitools.jackson.nullable.JsonNullable;
+import java.util.NoSuchElementException;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+
+/**
+ * Model tests for DefaultValue
+ */
+public class DefaultValueTest {
+    private final DefaultValue model = new DefaultValue();
+
+    /**
+     * Model tests for DefaultValue
+     */
+    @Test
+    public void testDefaultValue() {
+        // TODO: test DefaultValue
+    }
+
+    /**
+     * Test the property 'arrayStringEnumDefault'
+     */
+    @Test
+    public void arrayStringEnumDefaultTest() {
+        // TODO: test arrayStringEnumDefault
+    }
+
+    /**
+     * Test the property 'arrayStringDefault'
+     */
+    @Test
+    public void arrayStringDefaultTest() {
+        // TODO: test arrayStringDefault
+    }
+
+    /**
+     * Test the property 'arrayString'
+     */
+    @Test
+    public void arrayStringTest() {
+        // TODO: test arrayString
+    }
+
+    /**
+     * Test the property 'arrayStringNullable'
+     */
+    @Test
+    public void arrayStringNullableTest() {
+        // TODO: test arrayStringNullable
+    }
+
+    /**
+     * Test the property 'stringNullable'
+     */
+    @Test
+    public void stringNullableTest() {
+        // TODO: test stringNullable
+    }
+
+}

samples/client/echo_api/java/okhttp-gson/.openapi-generator/FILES

@@ -10,6 +10,7 @@ docs/BodyApi.md
 docs/Category.md
 docs/DataQuery.md
 docs/DataQueryAllOf.md
+docs/DefaultValue.md
 docs/PathApi.md
 docs/Pet.md
 docs/Query.md
@@ -51,6 +52,7 @@ src/main/java/org/openapitools/client/model/Bird.java
 src/main/java/org/openapitools/client/model/Category.java
 src/main/java/org/openapitools/client/model/DataQuery.java
 src/main/java/org/openapitools/client/model/DataQueryAllOf.java
+src/main/java/org/openapitools/client/model/DefaultValue.java
 src/main/java/org/openapitools/client/model/Pet.java
 src/main/java/org/openapitools/client/model/Query.java
 src/main/java/org/openapitools/client/model/Tag.java

samples/client/echo_api/java/okhttp-gson/README.md

@@ -129,6 +129,7 @@ Class | Method | HTTP request | Description
  - [Category](docs/Category.md)
  - [DataQuery](docs/DataQuery.md)
  - [DataQueryAllOf](docs/DataQueryAllOf.md)
+ - [DefaultValue](docs/DefaultValue.md)
  - [Pet](docs/Pet.md)
  - [Query](docs/Query.md)
  - [Tag](docs/Tag.md)

samples/client/echo_api/java/okhttp-gson/api/openapi.yaml

@@ -301,6 +301,47 @@ components:
       type: object
       xml:
         name: pet
+    DefaultValue:
+      description: to test the default value of properties
+      properties:
+        array_string_enum_default:
+          default:
+          - success
+          - failure
+          items:
+            enum:
+            - success
+            - failure
+            - unclassified
+            type: string
+          type: array
+        array_string_default:
+          default:
+          - failure
+          - skipped
+          items:
+            type: string
+          type: array
+        array_integer_default:
+          default:
+          - 1
+          - 3
+          items:
+            type: integer
+          type: array
+        array_string:
+          items:
+            type: string
+          type: array
+        array_string_nullable:
+          items:
+            type: string
+          nullable: true
+          type: array
+        string_nullable:
+          nullable: true
+          type: string
+      type: object
     Bird:
       properties:
         size:

samples/client/echo_api/java/okhttp-gson/docs/DefaultValue.md

@@ -0,0 +1,29 @@
+
+
+# DefaultValue
+
+to test the default value of properties
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**arrayStringEnumDefault** | [**List<ArrayStringEnumDefaultEnum>**](#List<ArrayStringEnumDefaultEnum>) |  |  [optional] |
+|**arrayStringDefault** | **List<String>** |  |  [optional] |
+|**arrayIntegerDefault** | **List<Integer>** |  |  [optional] |
+|**arrayString** | **List<String>** |  |  [optional] |
+|**arrayStringNullable** | **List<String>** |  |  [optional] |
+|**stringNullable** | **String** |  |  [optional] |
+
+
+
+## Enum: List<ArrayStringEnumDefaultEnum>
+
+| Name | Value |
+|---- | -----|
+| SUCCESS | "success" |
+| FAILURE | "failure" |
+| UNCLASSIFIED | "unclassified" |
+
+
+

samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/JSON.java

@@ -97,6 +97,7 @@ public class JSON {
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.Category.CustomTypeAdapterFactory());
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.DataQuery.CustomTypeAdapterFactory());
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.DataQueryAllOf.CustomTypeAdapterFactory());
+        gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.DefaultValue.CustomTypeAdapterFactory());
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.Pet.CustomTypeAdapterFactory());
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.Tag.CustomTypeAdapterFactory());
         gsonBuilder.registerTypeAdapterFactory(new org.openapitools.client.model.TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter.CustomTypeAdapterFactory());

samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/DefaultValue.java

@@ -0,0 +1,473 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import java.util.Objects;
+import java.util.Arrays;
+import com.google.gson.TypeAdapter;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonDeserializationContext;
+import com.google.gson.JsonDeserializer;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParseException;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.reflect.TypeToken;
+
+import java.lang.reflect.Type;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+import org.openapitools.client.JSON;
+
+/**
+ * to test the default value of properties
+ */
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class DefaultValue {
+  /**
+   * Gets or Sets arrayStringEnumDefault
+   */
+  @JsonAdapter(ArrayStringEnumDefaultEnum.Adapter.class)
+  public enum ArrayStringEnumDefaultEnum {
+    SUCCESS("success"),
+    
+    FAILURE("failure"),
+    
+    UNCLASSIFIED("unclassified");
+
+    private String value;
+
+    ArrayStringEnumDefaultEnum(String value) {
+      this.value = value;
+    }
+
+    public String getValue() {
+      return value;
+    }
+
+    @Override
+    public String toString() {
+      return String.valueOf(value);
+    }
+
+    public static ArrayStringEnumDefaultEnum fromValue(String value) {
+      for (ArrayStringEnumDefaultEnum b : ArrayStringEnumDefaultEnum.values()) {
+        if (b.value.equals(value)) {
+          return b;
+        }
+      }
+      throw new IllegalArgumentException("Unexpected value '" + value + "'");
+    }
+
+    public static class Adapter extends TypeAdapter<ArrayStringEnumDefaultEnum> {
+      @Override
+      public void write(final JsonWriter jsonWriter, final ArrayStringEnumDefaultEnum enumeration) throws IOException {
+        jsonWriter.value(enumeration.getValue());
+      }
+
+      @Override
+      public ArrayStringEnumDefaultEnum read(final JsonReader jsonReader) throws IOException {
+        String value =  jsonReader.nextString();
+        return ArrayStringEnumDefaultEnum.fromValue(value);
+      }
+    }
+  }
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_ENUM_DEFAULT = "array_string_enum_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_ENUM_DEFAULT)
+  private List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault = null;
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_DEFAULT = "array_string_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_DEFAULT)
+  private List<String> arrayStringDefault = null;
+
+  public static final String SERIALIZED_NAME_ARRAY_INTEGER_DEFAULT = "array_integer_default";
+  @SerializedName(SERIALIZED_NAME_ARRAY_INTEGER_DEFAULT)
+  private List<Integer> arrayIntegerDefault = null;
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING = "array_string";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING)
+  private List<String> arrayString = null;
+
+  public static final String SERIALIZED_NAME_ARRAY_STRING_NULLABLE = "array_string_nullable";
+  @SerializedName(SERIALIZED_NAME_ARRAY_STRING_NULLABLE)
+  private List<String> arrayStringNullable = null;
+
+  public static final String SERIALIZED_NAME_STRING_NULLABLE = "string_nullable";
+  @SerializedName(SERIALIZED_NAME_STRING_NULLABLE)
+  private String stringNullable;
+
+  public DefaultValue() {
+  }
+
+  public DefaultValue arrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringEnumDefaultItem(ArrayStringEnumDefaultEnum arrayStringEnumDefaultItem) {
+    if (this.arrayStringEnumDefault == null) {
+      this.arrayStringEnumDefault = new ArrayList<>(Arrays.asList(ArrayStringEnumDefaultEnum.SUCCESS, ArrayStringEnumDefaultEnum.FAILURE));
+    }
+    this.arrayStringEnumDefault.add(arrayStringEnumDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringEnumDefault
+   * @return arrayStringEnumDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<ArrayStringEnumDefaultEnum> getArrayStringEnumDefault() {
+    return arrayStringEnumDefault;
+  }
+
+
+  public void setArrayStringEnumDefault(List<ArrayStringEnumDefaultEnum> arrayStringEnumDefault) {
+    this.arrayStringEnumDefault = arrayStringEnumDefault;
+  }
+
+
+  public DefaultValue arrayStringDefault(List<String> arrayStringDefault) {
+    
+    this.arrayStringDefault = arrayStringDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayStringDefaultItem(String arrayStringDefaultItem) {
+    if (this.arrayStringDefault == null) {
+      this.arrayStringDefault = new ArrayList<>(Arrays.asList("failure", "skipped"));
+    }
+    this.arrayStringDefault.add(arrayStringDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringDefault
+   * @return arrayStringDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayStringDefault() {
+    return arrayStringDefault;
+  }
+
+
+  public void setArrayStringDefault(List<String> arrayStringDefault) {
+    this.arrayStringDefault = arrayStringDefault;
+  }
+
+
+  public DefaultValue arrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    
+    this.arrayIntegerDefault = arrayIntegerDefault;
+    return this;
+  }
+
+  public DefaultValue addArrayIntegerDefaultItem(Integer arrayIntegerDefaultItem) {
+    if (this.arrayIntegerDefault == null) {
+      this.arrayIntegerDefault = new ArrayList<>(Arrays.asList(1, 3));
+    }
+    this.arrayIntegerDefault.add(arrayIntegerDefaultItem);
+    return this;
+  }
+
+   /**
+   * Get arrayIntegerDefault
+   * @return arrayIntegerDefault
+  **/
+  @javax.annotation.Nullable
+
+  public List<Integer> getArrayIntegerDefault() {
+    return arrayIntegerDefault;
+  }
+
+
+  public void setArrayIntegerDefault(List<Integer> arrayIntegerDefault) {
+    this.arrayIntegerDefault = arrayIntegerDefault;
+  }
+
+
+  public DefaultValue arrayString(List<String> arrayString) {
+    
+    this.arrayString = arrayString;
+    return this;
+  }
+
+  public DefaultValue addArrayStringItem(String arrayStringItem) {
+    if (this.arrayString == null) {
+      this.arrayString = new ArrayList<>();
+    }
+    this.arrayString.add(arrayStringItem);
+    return this;
+  }
+
+   /**
+   * Get arrayString
+   * @return arrayString
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayString() {
+    return arrayString;
+  }
+
+
+  public void setArrayString(List<String> arrayString) {
+    this.arrayString = arrayString;
+  }
+
+
+  public DefaultValue arrayStringNullable(List<String> arrayStringNullable) {
+    
+    this.arrayStringNullable = arrayStringNullable;
+    return this;
+  }
+
+  public DefaultValue addArrayStringNullableItem(String arrayStringNullableItem) {
+    if (this.arrayStringNullable == null) {
+      this.arrayStringNullable = null;
+    }
+    this.arrayStringNullable.add(arrayStringNullableItem);
+    return this;
+  }
+
+   /**
+   * Get arrayStringNullable
+   * @return arrayStringNullable
+  **/
+  @javax.annotation.Nullable
+
+  public List<String> getArrayStringNullable() {
+    return arrayStringNullable;
+  }
+
+
+  public void setArrayStringNullable(List<String> arrayStringNullable) {
+    this.arrayStringNullable = arrayStringNullable;
+  }
+
+
+  public DefaultValue stringNullable(String stringNullable) {
+    
+    this.stringNullable = stringNullable;
+    return this;
+  }
+
+   /**
+   * Get stringNullable
+   * @return stringNullable
+  **/
+  @javax.annotation.Nullable
+
+  public String getStringNullable() {
+    return stringNullable;
+  }
+
+
+  public void setStringNullable(String stringNullable) {
+    this.stringNullable = stringNullable;
+  }
+
+
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    DefaultValue defaultValue = (DefaultValue) o;
+    return Objects.equals(this.arrayStringEnumDefault, defaultValue.arrayStringEnumDefault) &&
+        Objects.equals(this.arrayStringDefault, defaultValue.arrayStringDefault) &&
+        Objects.equals(this.arrayIntegerDefault, defaultValue.arrayIntegerDefault) &&
+        Objects.equals(this.arrayString, defaultValue.arrayString) &&
+        Objects.equals(this.arrayStringNullable, defaultValue.arrayStringNullable) &&
+        Objects.equals(this.stringNullable, defaultValue.stringNullable);
+  }
+
+  private static <T> boolean equalsNullable(JsonNullable<T> a, JsonNullable<T> b) {
+    return a == b || (a != null && b != null && a.isPresent() && b.isPresent() && Objects.deepEquals(a.get(), b.get()));
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(arrayStringEnumDefault, arrayStringDefault, arrayIntegerDefault, arrayString, arrayStringNullable, stringNullable);
+  }
+
+  private static <T> int hashCodeNullable(JsonNullable<T> a) {
+    if (a == null) {
+      return 1;
+    }
+    return a.isPresent() ? Arrays.deepHashCode(new Object[]{a.get()}) : 31;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder sb = new StringBuilder();
+    sb.append("class DefaultValue {\n");
+    sb.append("    arrayStringEnumDefault: ").append(toIndentedString(arrayStringEnumDefault)).append("\n");
+    sb.append("    arrayStringDefault: ").append(toIndentedString(arrayStringDefault)).append("\n");
+    sb.append("    arrayIntegerDefault: ").append(toIndentedString(arrayIntegerDefault)).append("\n");
+    sb.append("    arrayString: ").append(toIndentedString(arrayString)).append("\n");
+    sb.append("    arrayStringNullable: ").append(toIndentedString(arrayStringNullable)).append("\n");
+    sb.append("    stringNullable: ").append(toIndentedString(stringNullable)).append("\n");
+    sb.append("}");
+    return sb.toString();
+  }
+
+  /**
+   * Convert the given object to string with each line indented by 4 spaces
+   * (except the first line).
+   */
+  private String toIndentedString(Object o) {
+    if (o == null) {
+      return "null";
+    }
+    return o.toString().replace("\n", "\n    ");
+  }
+
+
+  public static HashSet<String> openapiFields;
+  public static HashSet<String> openapiRequiredFields;
+
+  static {
+    // a set of all properties/fields (JSON key names)
+    openapiFields = new HashSet<String>();
+    openapiFields.add("array_string_enum_default");
+    openapiFields.add("array_string_default");
+    openapiFields.add("array_integer_default");
+    openapiFields.add("array_string");
+    openapiFields.add("array_string_nullable");
+    openapiFields.add("string_nullable");
+
+    // a set of required properties/fields (JSON key names)
+    openapiRequiredFields = new HashSet<String>();
+  }
+
+ /**
+  * Validates the JSON Object and throws an exception if issues found
+  *
+  * @param jsonObj JSON Object
+  * @throws IOException if the JSON Object is invalid with respect to DefaultValue
+  */
+  public static void validateJsonObject(JsonObject jsonObj) throws IOException {
+      if (jsonObj == null) {
+        if (!DefaultValue.openapiRequiredFields.isEmpty()) { // has required fields but JSON object is null
+          throw new IllegalArgumentException(String.format("The required field(s) %s in DefaultValue is not found in the empty JSON string", DefaultValue.openapiRequiredFields.toString()));
+        }
+      }
+
+      Set<Entry<String, JsonElement>> entries = jsonObj.entrySet();
+      // check to see if the JSON string contains additional fields
+      for (Entry<String, JsonElement> entry : entries) {
+        if (!DefaultValue.openapiFields.contains(entry.getKey())) {
+          throw new IllegalArgumentException(String.format("The field `%s` in the JSON string is not defined in the `DefaultValue` properties. JSON: %s", entry.getKey(), jsonObj.toString()));
+        }
+      }
+      // ensure the optional json data is an array if present
+      if (jsonObj.get("array_string_enum_default") != null && !jsonObj.get("array_string_enum_default").isJsonArray()) {
+        throw new IllegalArgumentException(String.format("Expected the field `array_string_enum_default` to be an array in the JSON string but got `%s`", jsonObj.get("array_string_enum_default").toString()));
+      }
+      // ensure the optional json data is an array if present
+      if (jsonObj.get("array_string_default") != null && !jsonObj.get("array_string_default").isJsonArray()) {
+        throw new IllegalArgumentException(String.format("Expected the field `array_string_default` to be an array in the JSON string but got `%s`", jsonObj.get("array_string_default").toString()));
+      }
+      // ensure the optional json data is an array if present
+      if (jsonObj.get("array_integer_default") != null && !jsonObj.get("array_integer_default").isJsonArray()) {
+        throw new IllegalArgumentException(String.format("Expected the field `array_integer_default` to be an array in the JSON string but got `%s`", jsonObj.get("array_integer_default").toString()));
+      }
+      // ensure the optional json data is an array if present
+      if (jsonObj.get("array_string") != null && !jsonObj.get("array_string").isJsonArray()) {
+        throw new IllegalArgumentException(String.format("Expected the field `array_string` to be an array in the JSON string but got `%s`", jsonObj.get("array_string").toString()));
+      }
+      // ensure the optional json data is an array if present
+      if (jsonObj.get("array_string_nullable") != null && !jsonObj.get("array_string_nullable").isJsonArray()) {
+        throw new IllegalArgumentException(String.format("Expected the field `array_string_nullable` to be an array in the JSON string but got `%s`", jsonObj.get("array_string_nullable").toString()));
+      }
+      if ((jsonObj.get("string_nullable") != null && !jsonObj.get("string_nullable").isJsonNull()) && !jsonObj.get("string_nullable").isJsonPrimitive()) {
+        throw new IllegalArgumentException(String.format("Expected the field `string_nullable` to be a primitive type in the JSON string but got `%s`", jsonObj.get("string_nullable").toString()));
+      }
+  }
+
+  public static class CustomTypeAdapterFactory implements TypeAdapterFactory {
+    @SuppressWarnings("unchecked")
+    @Override
+    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+       if (!DefaultValue.class.isAssignableFrom(type.getRawType())) {
+         return null; // this class only serializes 'DefaultValue' and its subtypes
+       }
+       final TypeAdapter<JsonElement> elementAdapter = gson.getAdapter(JsonElement.class);
+       final TypeAdapter<DefaultValue> thisAdapter
+                        = gson.getDelegateAdapter(this, TypeToken.get(DefaultValue.class));
+
+       return (TypeAdapter<T>) new TypeAdapter<DefaultValue>() {
+           @Override
+           public void write(JsonWriter out, DefaultValue value) throws IOException {
+             JsonObject obj = thisAdapter.toJsonTree(value).getAsJsonObject();
+             elementAdapter.write(out, obj);
+           }
+
+           @Override
+           public DefaultValue read(JsonReader in) throws IOException {
+             JsonObject jsonObj = elementAdapter.read(in).getAsJsonObject();
+             validateJsonObject(jsonObj);
+             return thisAdapter.fromJsonTree(jsonObj);
+           }
+
+       }.nullSafe();
+    }
+  }
+
+ /**
+  * Create an instance of DefaultValue given an JSON string
+  *
+  * @param jsonString JSON string
+  * @return An instance of DefaultValue
+  * @throws IOException if the JSON string is invalid with respect to DefaultValue
+  */
+  public static DefaultValue fromJson(String jsonString) throws IOException {
+    return JSON.getGson().fromJson(jsonString, DefaultValue.class);
+  }
+
+ /**
+  * Convert an instance of DefaultValue to an JSON string
+  *
+  * @return JSON string
+  */
+  public String toJson() {
+    return JSON.getGson().toJson(this);
+  }
+}
+

samples/client/echo_api/java/okhttp-gson/src/main/java/org/openapitools/client/model/Query.java

@@ -140,7 +140,7 @@ public class Query {
 
   public Query addOutcomesItem(OutcomesEnum outcomesItem) {
     if (this.outcomes == null) {
-      this.outcomes = new ArrayList<>();
+      this.outcomes = new ArrayList<>(Arrays.asList(OutcomesEnum.SUCCESS, OutcomesEnum.FAILURE));
     }
     this.outcomes.add(outcomesItem);
     return this;

samples/client/echo_api/java/okhttp-gson/src/test/java/org/openapitools/client/model/DefaultValueTest.java

@@ -0,0 +1,91 @@
+/*
+ * Echo Server API
+ * Echo Server API
+ *
+ * The version of the OpenAPI document: 0.1.0
+ * Contact: team@openapitools.org
+ *
+ * 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.model;
+
+import com.google.gson.TypeAdapter;
+import com.google.gson.annotations.JsonAdapter;
+import com.google.gson.annotations.SerializedName;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.openapitools.jackson.nullable.JsonNullable;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
+
+
+/**
+ * Model tests for DefaultValue
+ */
+public class DefaultValueTest {
+    private final DefaultValue model = new DefaultValue();
+
+    /**
+     * Model tests for DefaultValue
+     */
+    @Test
+    public void testDefaultValue() {
+        // TODO: test DefaultValue
+    }
+
+    /**
+     * Test the property 'arrayStringEnumDefault'
+     */
+    @Test
+    public void arrayStringEnumDefaultTest() {
+        // TODO: test arrayStringEnumDefault
+    }
+
+    /**
+     * Test the property 'arrayStringDefault'
+     */
+    @Test
+    public void arrayStringDefaultTest() {
+        // TODO: test arrayStringDefault
+    }
+
+    /**
+     * Test the property 'arrayIntegerDefault'
+     */
+    @Test
+    public void arrayIntegerDefaultTest() {
+        // TODO: test arrayIntegerDefault
+    }
+
+    /**
+     * Test the property 'arrayString'
+     */
+    @Test
+    public void arrayStringTest() {
+        // TODO: test arrayString
+    }
+
+    /**
+     * Test the property 'arrayStringNullable'
+     */
+    @Test
+    public void arrayStringNullableTest() {
+        // TODO: test arrayStringNullable
+    }
+
+    /**
+     * Test the property 'stringNullable'
+     */
+    @Test
+    public void stringNullableTest() {
+        // TODO: test stringNullable
+    }
+
+}