[Bugfix][Java] Fixed jersey clients for multiple file upload (#19476)

* Fixed jersey3 client for multiple file upload

* Updated sample

* Fixed typo

* Fix

* Fix for jersey2

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

@@ -988,24 +988,10 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -1034,6 +1020,36 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

modules/openapi-generator/src/main/resources/Java/libraries/jersey3/ApiClient.mustache

@@ -988,24 +988,10 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -1034,6 +1020,36 @@ public class ApiClient{{#jsr310}} extends JavaTimeFormatter{{/jsr310}} {
     return entity;
   }
 
+  /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/client/others/java/jersey2-oneOf-Mixed/src/main/java/org/openapitools/client/ApiClient.java

@@ -767,24 +767,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -813,6 +799,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/client/others/java/jersey2-oneOf-duplicates/src/main/java/org/openapitools/client/ApiClient.java

@@ -767,24 +767,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -813,6 +799,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/client/petstore/java/jersey2-java8-localdatetime/src/main/java/org/openapitools/client/ApiClient.java

@@ -908,24 +908,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -954,6 +940,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java

@@ -908,24 +908,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -954,6 +940,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/client/petstore/java/jersey3/src/main/java/org/openapitools/client/ApiClient.java

@@ -990,24 +990,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -1036,6 +1022,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+  /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/openapi3/client/extensions/x-auth-id-alias/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java

@@ -816,24 +816,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -862,6 +848,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/openapi3/client/petstore/java/jersey2-java8-special-characters/src/main/java/org/openapitools/client/ApiClient.java

@@ -767,24 +767,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -813,6 +799,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/openapi3/client/petstore/java/jersey2-java8-swagger1/src/main/java/org/openapitools/client/ApiClient.java

@@ -892,24 +892,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -938,6 +924,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/openapi3/client/petstore/java/jersey2-java8-swagger2/src/main/java/org/openapitools/client/ApiClient.java

@@ -892,24 +892,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -938,6 +924,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).

samples/openapi3/client/petstore/java/jersey2-java8/src/main/java/org/openapitools/client/ApiClient.java

@@ -990,24 +990,10 @@ public class ApiClient extends JavaTimeFormatter {
     if (contentType.startsWith("multipart/form-data")) {
       MultiPart multiPart = new MultiPart();
       for (Entry<String, Object> param: formParams.entrySet()) {
-        if (param.getValue() instanceof File) {
+        if (param.getValue() instanceof Iterable) {
-          File file = (File) param.getValue();
+          ((Iterable)param.getValue()).forEach(v -> addParamToMultipart(v, param.getKey(), multiPart));
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey())
-              .fileName(file.getName()).size(file.length()).build();
-
-          // Attempt to probe the content type for the file so that the form part is more correctly
-          // and precisely identified, but fall back to application/octet-stream if that fails.
-          MediaType type;
-          try {
-            type = MediaType.valueOf(Files.probeContentType(file.toPath()));
-          } catch (IOException | IllegalArgumentException e) {
-            type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
-          }
-
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
         } else {
-          FormDataContentDisposition contentDisp = FormDataContentDisposition.name(param.getKey()).build();
+          addParamToMultipart(param.getValue(), param.getKey(), multiPart);
-          multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(param.getValue())));
         }
       }
       entity = Entity.entity(multiPart, MediaType.MULTIPART_FORM_DATA_TYPE);
@@ -1036,6 +1022,36 @@ public class ApiClient extends JavaTimeFormatter {
     return entity;
   }
 
+    /**
+   * Adds the object with the provided key to the MultiPart.
+   * Based on the object type sets Content-Disposition and Content-Type.
+   *
+   * @param obj Object
+   * @param key Key of the object
+   * @param multiPart MultiPart to add the form param to
+   */
+  private void addParamToMultipart(Object value, String key, MultiPart multiPart) {
+    if (value instanceof File) {
+      File file = (File) value;
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key)
+          .fileName(file.getName()).size(file.length()).build();
+
+      // Attempt to probe the content type for the file so that the form part is more correctly
+      // and precisely identified, but fall back to application/octet-stream if that fails.
+      MediaType type;
+      try {
+        type = MediaType.valueOf(Files.probeContentType(file.toPath()));
+      } catch (IOException | IllegalArgumentException e) {
+        type = MediaType.APPLICATION_OCTET_STREAM_TYPE;
+      }
+
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, file, type));
+    } else {
+      FormDataContentDisposition contentDisp = FormDataContentDisposition.name(key).build();
+      multiPart.bodyPart(new FormDataBodyPart(contentDisp, parameterToString(value)));
+    }
+  } 
+
   /**
    * Serialize the given Java object into string according the given
    * Content-Type (only JSON, HTTP form is supported for now).