/*
    * 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 javax.servlet.http.HttpServletResponse;
  
  import org.springframework.core.MethodParameter;
  import org.springframework.http.HttpHeaders;
  import org.springframework.http.server.ServletServerHttpResponse;
  import org.springframework.util.Assert;
  import org.springframework.web.context.request.NativeWebRequest;
  import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
  import org.springframework.web.method.support.ModelAndViewContainer;
  
  /**
   * Handles {@link HttpHeaders} return values.
   *
   * @author Stephane Nicoll
   * @since 4.0.1
   */
  public class HttpHeadersReturnValueHandler implements HandlerMethodReturnValueHandler {
  
  	@Override
  	public boolean supportsReturnType(MethodParameter returnType) {
  		return HttpHeaders.class.isAssignableFrom(returnType.getParameterType());
  	}
  
  	@Override
  	@SuppressWarnings("resource")
  	public void handleReturnValue(Object returnValue, MethodParameter returnType,
  			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
  
  		mavContainer.setRequestHandled(true);
  
  		Assert.isInstanceOf(HttpHeaders.class, returnValue);
  		HttpHeaders headers = (HttpHeaders) returnValue;
  
  		if (!headers.isEmpty()) {
  			HttpServletResponse servletResponse = webRequest.getNativeResponse(HttpServletResponse.class);
  			ServletServerHttpResponse outputMessage = new ServletServerHttpResponse(servletResponse);
  			outputMessage.getHeaders().putAll(headers);
  			outputMessage.getBody(); // flush headers
  		}
  	}
  
  }