Fix customized source folder in Java client (#1978)

* fix customized source folder in java client

* update samples

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

@@ -349,6 +349,7 @@ public abstract class AbstractJavaCodegen extends DefaultCodegen implements Code
         if (additionalProperties.containsKey(CodegenConstants.SOURCE_FOLDER)) {
             this.setSourceFolder((String) additionalProperties.get(CodegenConstants.SOURCE_FOLDER));
         }
+        additionalProperties.put(CodegenConstants.SOURCE_FOLDER, sourceFolder);
 
         if (additionalProperties.containsKey(CodegenConstants.LOCAL_VARIABLE_PREFIX)) {
             this.setLocalVariablePrefix((String) additionalProperties.get(CodegenConstants.LOCAL_VARIABLE_PREFIX));

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

@@ -1,5 +1,8 @@
 apply plugin: 'idea'
 apply plugin: 'eclipse'
+{{#sourceFolder}}
+apply plugin: 'java'
+{{/sourceFolder}}
 
 group = '{{groupId}}'
 version = '{{artifactVersion}}'
@@ -18,8 +21,12 @@ buildscript {
 repositories {
     jcenter()
 }
+{{#sourceFolder}}
+sourceSets {
+    main.java.srcDirs = ['{{sourceFolder}}']
+}
 
-
+{{/sourceFolder}}
 if(hasProperty('target') && target == 'android') {
 
     apply plugin: 'com.android.library'

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

@@ -121,8 +121,7 @@
                         </goals>
                         <configuration>
                             <sources>
-                                <source>
-                                src/main/java</source>
+                                <source>{{{sourceFolder}}}</source>
                             </sources>
                         </configuration>
                     </execution>
@@ -134,8 +133,7 @@
                         </goals>
                         <configuration>
                             <sources>
-                                <source>
-                                src/test/java</source>
+                                <source>src/test/java</source>
                             </sources>
                         </configuration>
                     </execution>