21、SpringMVC源码分析 - HandlerMethodReturnValueHandler

前言

HandlerMethodReturnValueHandler用于对接口返回值的处理。

一、HandlerMethodReturnValueHandler

public interface HandlerMethodReturnValueHandler {
   
     

	//是否支持返回值的类型
	boolean supportsReturnType(MethodParameter returnType);

	//对返回值进行处理
	void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;

}

二、ModelAndViewMethodReturnValueHandler

用于处理ModelAndView类型

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		//返回值是ModelAndView类型
		return ModelAndView.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     
		//返回值是null
		if (returnValue == null) {
   
     
			mavContainer.setRequestHandled(true);
			return;
		}

		ModelAndView mav = (ModelAndView) returnValue;
		//view是否是String类型
		if (mav.isReference()) {
   
     
			String viewName = mav.getViewName();
			mavContainer.setViewName(viewName);
			//是否是重定向
			if (viewName != null && isRedirectViewName(viewName)) {
   
     
				mavContainer.setRedirectModelScenario(true);
			}
		}
		else {
   
     
			//处理View类型
			View view = mav.getView();
			mavContainer.setView(view);
			//重定向
			if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
   
     
				mavContainer.setRedirectModelScenario(true);
			}
		}
		mavContainer.setStatus(mav.getStatus());
		mavContainer.addAllAttributes(mav.getModel());
	}

三、ModelMethodProcessor

用于处理Model类型

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		//返回值是Model类型
		return Model.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     

		if (returnValue == null) {
   
     
			return;
		}
		else if (returnValue instanceof Model) {
   
     
			//Model类型，将model的参数添加到ModelMap中
			mavContainer.addAllAttributes(((Model) returnValue).asMap());
		}
		else {
   
     
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type [" +
					returnType.getParameterType().getName() + "] in method: " + returnType.getMethod());
		}
	}

四、ViewMethodReturnValueHandler

用于处理View类型

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		//返回值是View类型
		return View.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     

		if (returnValue instanceof View) {
   
     
			View view = (View) returnValue;
			//设置view
			mavContainer.setView(view);
			//校验重定向
			if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
   
     
				mavContainer.setRedirectModelScenario(true);
			}
		}
		else if (returnValue != null) {
   
     
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type: " +
					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
		}
	}

五、HttpEntityMethodProcessor

用于处理HttpEntity、ResponseEntity类型

	@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		//返回值是HttpEntity类型，并且不能是RequestEntity类型
		return (HttpEntity.class.isAssignableFrom(returnType.getParameterType()) &&
				!RequestEntity.class.isAssignableFrom(returnType.getParameterType()));
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     

		mavContainer.setRequestHandled(true);
		if (returnValue == null) {
   
     
			return;
		}
		//request
		ServletServerHttpRequest inputMessage = createInputMessage(webRequest);
		//response
		ServletServerHttpResponse outputMessage = createOutputMessage(webRequest);

		//returnValue是HttpEntity类型
		Assert.isInstanceOf(HttpEntity.class, returnValue);
		HttpEntity<?> responseEntity = (HttpEntity<?>) returnValue;

		HttpHeaders outputHeaders = outputMessage.getHeaders();
		HttpHeaders entityHeaders = responseEntity.getHeaders();
		//设置响应的headers
		if (!entityHeaders.isEmpty()) {
   
     
			entityHeaders.forEach((key, value) -> {
   
     
				if (HttpHeaders.VARY.equals(key) && outputHeaders.containsKey(HttpHeaders.VARY)) {
   
     
					List<String> values = getVaryRequestHeadersToAdd(outputHeaders, entityHeaders);
					if (!values.isEmpty()) {
   
     
						outputHeaders.setVary(values);
					}
				}
				else {
   
     
					outputHeaders.put(key, value);
				}
			});
		}
		
		//ResponseEntity类型
		if (responseEntity instanceof ResponseEntity) {
   
     
			int returnStatus = ((ResponseEntity<?>) responseEntity).getStatusCodeValue();
			outputMessage.getServletResponse().setStatus(returnStatus);
			if (returnStatus == 200) {
   
     
				HttpMethod method = inputMessage.getMethod();
				//get和head方法，校验资源是否没有修改过，没有修改直接返回
				if ((HttpMethod.GET.equals(method) || HttpMethod.HEAD.equals(method))
						&& isResourceNotModified(inputMessage, outputMessage)) {
   
     
					outputMessage.flush();
					return;
				}
			}
			else if (returnStatus / 100 == 3) {
   
     
				String location = outputHeaders.getFirst("location");
				if (location != null) {
   
     
					//处理重定向
					saveFlashAttributes(mavContainer, webRequest, location);
				}
			}
		}

		// Try even with null body. ResponseBodyAdvice could get involved.
		//通过MessageConverters填充body
		writeWithMessageConverters(responseEntity.getBody(), returnType, inputMessage, outputMessage);

		// Ensure headers are flushed even if no body was written.
		outputMessage.flush();
	}

六、 MapMethodProcessor

用于处理Map类型

@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		//Map类型
		return Map.class.isAssignableFrom(returnType.getParameterType());
	}

	@Override
	@SuppressWarnings({
   
     "rawtypes", "unchecked"})
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     

		if (returnValue instanceof Map){
   
     
			//将Map中参数设置到ModelMap中
			mavContainer.addAllAttributes((Map) returnValue);
		}
		else if (returnValue != null) {
   
     
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type [" +
					returnType.getParameterType().getName() + "] in method: " + returnType.getMethod());
		}
	}

七、 ViewNameMethodReturnValueHandler

用于处理void和CharSequence类型

@Override
	public boolean supportsReturnType(MethodParameter returnType) {
   
     
		Class<?> paramType = returnType.getParameterType();
		return (void.class == paramType || CharSequence.class.isAssignableFrom(paramType));
	}

	@Override
	public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
   
     

		if (returnValue instanceof CharSequence) {
   
     
			String viewName = returnValue.toString();
			mavContainer.setViewName(viewName);
			if (isRedirectViewName(viewName)) {
   
     
				mavContainer.setRedirectModelScenario(true);
			}
		}
		else if (returnValue != null) {
   
     
			// should not happen
			throw new UnsupportedOperationException("Unexpected return type: " +
					returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
		}
	}