title: @Async in Rest Controller not working
body: <p>I am developing a REST API and want to make it as an asynchronous Rest Controller,
  So my Controller is below:</p>
  
  <pre><code>@RestController
  @Async
  public class ApiController {
      List&lt;ApiObject&gt;  apiDataList;   
  
      @RequestMapping(value="/data",produces={MediaType.APPLICATION_JSON_VALUE},method=RequestMethod.GET)
      public ResponseEntity&lt;List&lt;ApiObject&gt;&gt; getData(){                                       
          List&lt;ApiObject&gt; apiDataList=getApiData();
          return new ResponseEntity&lt;List&lt;ApiObject&gt;&gt;(apiDataList,HttpStatus.OK);
      }
      @ResponseBody   
      public List&lt;ApiObject&gt;  getApiData(){
          List&lt;ApiObject&gt;  apiDataList3=new List&lt;ApiObject&gt; ();
          //do the processing
          return apiDataList3;
      }
  }
  </code></pre>
  
  <p>Then in the Spring boot Application class I created as </p>
  
  <pre><code>@SpringBootApplication
  @EnableScheduling
  @EnableCaching
  @EnableAsync
  
  public class APIApplication {
  
      public static void main(String[] args) {
          SpringApplication.run(APIApplication.class, args);
      }
  
  
  }
  </code></pre>
  
  <p>After that in the server.xml I tried to add the Nio Connector like below:</p>
  
  <pre><code>&lt;Connector maxThreads="1000" port="8080" protocol="org.apache.coyote.http11.Http11Nioprotocol"
                 connectionTimeout="20000"
                 redirectPort="8443" /&gt;
  </code></pre>
  
  <p>But the Application starts but the response is empty.Any help is appreciated</p>