How to use

DeferredResultMethodReturnValueHandler

in

org.springframework.web.servlet.mvc.method.annotation

handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));

@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
    ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
  if (returnValue == null) {
    mavContainer.setRequestHandled(true);
    return;
  }
  DeferredResult<?> result;
  if (returnValue instanceof DeferredResult) {
    result = (DeferredResult<?>) returnValue;
  }
  else if (returnValue instanceof ListenableFuture) {
    result = adaptListenableFuture((ListenableFuture<?>) returnValue);
  }
  else if (returnValue instanceof CompletionStage) {
    result = adaptCompletionStage((CompletionStage<?>) returnValue);
  }
  else {
    // Should not happen...
    throw new IllegalStateException("Unexpected return value type: " + returnValue);
  }
  WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(result, mavContainer);
}

@Test
public void supportsReturnType() throws Exception {
  assertTrue(this.handler.supportsReturnType(
      on(TestController.class).resolveReturnType(DeferredResult.class, String.class)));
  assertTrue(this.handler.supportsReturnType(
      on(TestController.class).resolveReturnType(ListenableFuture.class, String.class)));
  assertTrue(this.handler.supportsReturnType(
      on(TestController.class).resolveReturnType(CompletableFuture.class, String.class)));
}

private void testHandle(Object returnValue, Class<?> asyncType,
    Runnable setResultTask, Object expectedValue) throws Exception {
  ModelAndViewContainer mavContainer = new ModelAndViewContainer();
  MethodParameter returnType = on(TestController.class).resolveReturnType(asyncType, String.class);
  this.handler.handleReturnValue(returnValue, returnType, mavContainer, this.webRequest);
  assertTrue(this.request.isAsyncStarted());
  assertFalse(WebAsyncUtils.getAsyncManager(this.webRequest).hasConcurrentResult());
  setResultTask.run();
  assertTrue(WebAsyncUtils.getAsyncManager(this.webRequest).hasConcurrentResult());
  assertEquals(expectedValue, WebAsyncUtils.getAsyncManager(this.webRequest).getConcurrentResult());
}

handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));

@Override
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
    ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
  if (returnValue == null) {
    mavContainer.setRequestHandled(true);
    return;
  }
  DeferredResult<?> result;
  if (returnValue instanceof DeferredResult) {
    result = (DeferredResult<?>) returnValue;
  }
  else if (returnValue instanceof ListenableFuture) {
    result = adaptListenableFuture((ListenableFuture<?>) returnValue);
  }
  else if (returnValue instanceof CompletionStage) {
    result = adaptCompletionStage((CompletionStage<?>) returnValue);
  }
  else {
    // Should not happen...
    throw new IllegalStateException("Unexpected return value type: " + returnValue);
  }
  WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(result, mavContainer);
}

@Test
public void doesNotSupportReturnType() throws Exception {
  assertFalse(this.handler.supportsReturnType(on(TestController.class).resolveReturnType(String.class)));
}

@Before
public void setup() throws Exception {
  this.handler = new DeferredResultMethodReturnValueHandler();
  this.request = new MockHttpServletRequest();
  MockHttpServletResponse response = new MockHttpServletResponse();
  this.webRequest = new ServletWebRequest(this.request, response);
  AsyncWebRequest asyncWebRequest = new StandardServletAsyncWebRequest(this.request, response);
  WebAsyncUtils.getAsyncManager(this.webRequest).setAsyncWebRequest(asyncWebRequest);
  this.request.setAsyncSupported(true);
}

handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));

handlers.add(new HttpEntityMethodProcessor(getMessageConverters(), this.contentNegotiationManager));
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));

handlers.add(new HttpHeadersReturnValueHandler());
handlers.add(new CallableMethodReturnValueHandler());
handlers.add(new DeferredResultMethodReturnValueHandler());
handlers.add(new AsyncTaskMethodReturnValueHandler(this.beanFactory));