[Java][jaxrs-jersey] unnecessary multipart imports in generated code

Description

if the java jaxrs-jersey server code is generated from a model which doesn't need the jersey multipart feature, the multipart packages are imported anyway.

openapi-generator version

openapi-generator 3.3.2

OpenAPI declaration file content or url

openapi: 3.0.1
info:
  title: foo
  description: >-
    bar
  version: 1.1.0
paths:
  /foo/v1/bar:
    get:
      summary: read foo bar
      operationId: getFooBar
      responses:
        200:
          content:
            application/json:
              schema:
                default:
          description: all went ok

Command line used for generation

Java -jar openapi-generator-cli-3.3.2.jar generate -i /foobar.yaml -g jaxrs-jersey -o /foobar

java output

package fooBar.impl;

import fooBar.*;
import fooBar.model.*;


import java.util.List;
import fooBar.NotFoundException;

import java.io.InputStream;

import org.glassfish.jersey.media.multipart.FormDataContentDisposition;

import javax.ws.rs.core.Response;
import javax.ws.rs.core.SecurityContext;
import javax.validation.constraints.*;
@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaJerseyServerCodegen", date = "2018-11-12T10:51:46.203+01:00[Europe/Berlin]")
public class FooApiServiceImpl extends FooApiService {
    @Override
    public Response getFooBar(SecurityContext securityContext) throws NotFoundException {
        // do some magic!
        return Response.ok().entity(new ApiResponseMessage(ApiResponseMessage.OK, "magic!")).build();
    }
}

Suggest a fix/enhancement

in the templates should be a check around the multipart imports:

{{#useMultipartFeature}}
import org.glassfish.jersey.media.multipart.FormDataContentDisposition;
import org.glassfish.jersey.media.multipart.FormDataParam;
{{/useMultipartFeature}}

Start with the jaxrs-jersey templates and reproduce the supplied Java generation command using the minimal OpenAPI YAML. Check how multipart imports are emitted when the model has no multipart feature, then verify generation still includes them for multipart endpoints. Done means unused multipart imports are absent without breaking cases that need them.