title: Asynchronous REST API generating warning
body: <p>I am working with a Spring boot application. I have a rest controller that returns Callable.</p>
  
  <pre><code>@GetMapping("/fb-roles")
  @Timed
  public Callable&lt;List&lt;FbRole&gt;&gt; getAllFbRoles() {
      log.debug("REST request to get all FbRoles");
      return (() -&gt; { return fbRoleRepository.findAll(); });
  }
  </code></pre>
  
  <p>A ThreadPoolTaskExecutor is configures as follow:</p>
  
  <pre><code>@Configuration
  @EnableAsync
  @EnableScheduling
  public class AsyncConfiguration implements AsyncConfigurer {
  
  private final Logger log = LoggerFactory.getLogger(AsyncConfiguration.class);
  
  private final JHipsterProperties jHipsterProperties;
  
  public AsyncConfiguration(JHipsterProperties jHipsterProperties) {
      this.jHipsterProperties = jHipsterProperties;
  }
  
  @Override
  @Bean(name = "taskExecutor")
  public Executor getAsyncExecutor() {
      log.debug("Creating Async Task Executor");
      ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
      executor.setCorePoolSize(jHipsterProperties.getAsync().getCorePoolSize());
      executor.setMaxPoolSize(jHipsterProperties.getAsync().getMaxPoolSize());
      executor.setQueueCapacity(jHipsterProperties.getAsync().getQueueCapacity());
      executor.setThreadNamePrefix("fb-quiz-Executor-");
      return new ExceptionHandlingAsyncTaskExecutor(executor);
  }
  
  @Override
  public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
      return new SimpleAsyncUncaughtExceptionHandler();
  }
  </code></pre>
  
  <p>}</p>
  
  <blockquote>
    <p>2018-09-19 00:43:58.434  WARN 10104 --- [ XNIO-2 task-28] o.s.w.c.request.async.WebAsyncManager    :
    !!!
    An Executor is required to handle java.util.concurrent.Callable return values.
    Please, configure a TaskExecutor in the MVC config under "async support".
    The SimpleAsyncTaskExecutor currently in use is not suitable under load.</p>
  </blockquote>
  
  <p>But while accessing the api server is producing the following warning</p>