Swagger Codegen does not support PATCH request

Description

Swagger-codegen Plugin does not support PATCH request to be made using Swagger generated Classes. The workaround around this issue as far as I know is to add line in invokeAPI method of ApiClient class
target.property(HttpUrlConnectorProvider.SET_METHOD_WORKAROUND, true);

public <T> ApiResponse<T> invokeAPI(String path, String method, List<Pair> queryParams, Object body, Map<String, String> headerParams, Map<String, Object> formParams, String accept, String contentType, String[] authNames, GenericType<T> returnType) throws ApiException {
    updateParamsForAuth(authNames, queryParams, headerParams);

    // Not using `.target(this.basePath).path(path)` below,
    // to support (constant) query string in `path`, e.g. "/posts?draft=1"
    WebTarget target = httpClient.target(this.basePath + path);
    target.property(HttpUrlConnectorProvider.SET_METHOD_WORKAROUND, true);

    if (queryParams != null) {
      for (Pair queryParam : queryParams) {
        if (queryParam.getValue() != null) {
          target = target.queryParam(queryParam.getName(), queryParam.getValue());
        }
      }
    }

    Invocation.Builder invocationBuilder = target.request().accept(accept);

    for (Entry<String, String> entry : headerParams.entrySet()) {
      String value = entry.getValue();
      if (value != null) {
        invocationBuilder = invocationBuilder.header(entry.getKey(), value);
      }
    }

    for (Entry<String, String> entry : defaultHeaderMap.entrySet()) {
      String key = entry.getKey();
      if (!headerParams.containsKey(key)) {
        String value = entry.getValue();
        if (value != null) {
          invocationBuilder = invocationBuilder.header(key, value);
        }
      }
    }

    Entity<?> entity = serialize(body, formParams, contentType);

    Response response = null;

    try {
      if ("GET".equals(method)) {
        response = invocationBuilder.get();
      } else if ("POST".equals(method)) {
        response = invocationBuilder.post(entity);
      } else if ("PUT".equals(method)) {
        response = invocationBuilder.put(entity);
      } else if ("DELETE".equals(method)) {
        response = invocationBuilder.delete();
      } else if ("PATCH".equals(method)) {
        response = invocationBuilder.method("PATCH", entity);
      } else if ("HEAD".equals(method)) {
        response = invocationBuilder.head();
      } else {
        throw new ApiException(500, "unknown method type " + method);
      }

      int statusCode = response.getStatusInfo().getStatusCode();
      Map<String, List<String>> responseHeaders = buildResponseHeaders(response);

      if (response.getStatus() == Status.NO_CONTENT.getStatusCode()) {
        return new ApiResponse<>(statusCode, responseHeaders);
      } else if (response.getStatusInfo().getFamily() == Status.Family.SUCCESSFUL) {
        if (returnType == null)
          return new ApiResponse<>(statusCode, responseHeaders);
        else
          return new ApiResponse<>(statusCode, responseHeaders, deserialize(response, returnType));
      } else {
        String message = "error";
        String respBody = null;
        if (response.hasEntity()) {
          try {
            respBody = String.valueOf(response.readEntity(String.class));
            message = respBody;
          } catch (RuntimeException e) {
            // e.printStackTrace();
          }
        }
        throw new ApiException(
          response.getStatus(),
          message,
          buildResponseHeaders(response),
          respBody);
      }
    } finally {
      try {
        response.close();
      } catch (Exception e) {
        // it's not critical, since the response object is local in method invokeAPI; that's fine, just continue
      }
    }
  }

Swagger-codegen version

swagger codegen - 2.3.1

Locate the generated ApiClient.invokeAPI method described in the issue and trace the Java client template that produces it. Verify how PATCH requests are currently sent in swagger-codegen 2.3.1, then ensure generated clients support PATCH without the reported workaround and confirm the behavior with the project's relevant tests.