/*
    * Copyright 2002-2014 the original author or authors.
    *
    * Licensed under the Apache License, Version 2.0 (the "License");
    * you may not use this file except in compliance with the License.
    * You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.springframework.web.servlet.mvc.method.annotation;
  
  import org.springframework.core.MethodParameter;
  import org.springframework.util.concurrent.ListenableFuture;
  import org.springframework.util.concurrent.ListenableFutureCallback;
  import org.springframework.web.context.request.NativeWebRequest;
  import org.springframework.web.context.request.async.DeferredResult;
  import org.springframework.web.context.request.async.WebAsyncUtils;
  import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
  import org.springframework.web.method.support.ModelAndViewContainer;
  
  /**
   * Handles return values of type
   * {@link org.springframework.util.concurrent.ListenableFuture}.
   *
   * @author Rossen Stoyanchev
   * @since 4.1
   */
  public class ListenableFutureReturnValueHandler implements HandlerMethodReturnValueHandler {
  
  	@Override
  	public boolean supportsReturnType(MethodParameter returnType) {
  		return ListenableFuture.class.isAssignableFrom(returnType.getParameterType());
  	}
  
  	@Override
  	public void handleReturnValue(Object returnValue, MethodParameter returnType,
  			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
  
  		if (returnValue == null) {
  			mavContainer.setRequestHandled(true);
  			return;
  		}
  
  		final DeferredResult<Object> deferredResult = new DeferredResult<Object>();
  		WebAsyncUtils.getAsyncManager(webRequest).startDeferredResultProcessing(deferredResult, mavContainer);
  
  		ListenableFuture<?> future = (ListenableFuture<?>) returnValue;
  		future.addCallback(new ListenableFutureCallback<Object>() {
  			@Override
  			public void onSuccess(Object result) {
  				deferredResult.setResult(result);
  			}
  			@Override
  			public void onFailure(Throwable ex) {
  				deferredResult.setErrorResult(ex);
  			}
  		});
  	}
  
  }