文章目录

前言

前言

SpringMVC是一个应用于表现层的经典框架，其中M代表模型（数据模型[pojo/vo/po]+业务模型）主要作用是充当C——>V的数据传递介质，V代表view视图（jps、html）负责请求域中M的展示，C代表Controller控制器（Servlet）主要作用是接收请求调用业务层进行业务处理，并将处理结果转发到V或者直接响应给浏览器。
SpringMVC请求处理流程较为宏观的描述

请求到达DispatcherServlet（前端控制器）后，DispatcherServlet调用HandlerMapping（处理器映射器）查询对应handler（处理器）
HandlerMapping根据请求的url获取对应的handler给到DispatcherServlet
DispatcherServlet将获取到的handler给到HandlerAdapter（处理器适配器）执行处理器处理请求业务
handler执行后返回ModelAndView给DispatcherServlet
DispatcherServlet请求视图解析器去解析view根据逻辑视图名拼接前后缀获取真正视图
DispatcherServlet将数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染
将渲染完成的视图响应给浏览器
由上述流程可以看出DispatcherServlet是负责串联SpringMVC各大组件的核心类，同时也是第一个接触Request的类，我们的源码剖析之旅就从DispatcherServlet入手。

前端控制器DispatcherServlet的继承结构分析及请求处理传递流程（一图胜万语）

在这里插入图片描述
doDispatch源码：

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    
		HttpServletRequest processedRequest = request;
		// 声明handler执行器链包含handler和拦截器数组
		HandlerExecutionChain mappedHandler = null;
		boolean multipartRequestParsed = false;
		//
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
    
    
			// 声明ModelAndView
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {
    
    
				// 检查是否文件上传请求如果是则返回MultipartHttpServletRequest不是则返回request原值
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				// 1.根据请求url获取handler执行器链包含处理当前请求的处理器对象和拦截器链
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
    
    
					// 如果handler链为空，则返回404
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				// 2.根据handler链中的handler处理器获取对应的处理器适配器（由于handler的格式不固定有可能是实现Controller接口的类，
				// 有可能是标记@RequestMapping的方法，所以不同的handler要对应不同适配器来执行handler业务逻辑）
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				if (isGet || "HEAD".equals(method)) {
    
    
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
    
    
						return;
					}
				}
				// 3.依次执行handler链中拦截器数组中拦截器的preHandler方法，返回true继续执行，false直接return
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    
    
					return;
				}

				// Actually invoke the handler.
				// 4.使用刚刚获取的HandlerAdapter处理器适配器执行handler逻辑，返回ModelAndView对象。
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
    
    
					return;
				}
                // 5.结果视图对象处理（如果未指定view逻辑视图名则根据请求路径给一个默认的逻辑视图名称）
				applyDefaultViewName(processedRequest, mv);
				// 6.依次执行handler链中拦截器数组中拦截器的postHandle方法
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
    
    
				dispatchException = ex;
			}
			catch (Throwable err) {
    
    
				// As of 4.3, we're processing Errors thrown from handler methods as well,
				// making them available for @ExceptionHandler methods and other scenarios.
				dispatchException = new NestedServletException("Handler dispatch failed", err);
			}
			// 7.数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
    
    
			// 8.依次执行handler链中拦截器数组中拦截器的afterCompletion方法
			//⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
    
    
			// 同8
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new NestedServletException("Handler processing failed", err));
		}
		finally {
    
    
			if (asyncManager.isConcurrentHandlingStarted()) {
    
    
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
    
    
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
    
    
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
    
    
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

提示：下面将按照doDispatch中的请求处理流程的8个主要流程逐一分析

1.根据请求url获取handler执行器链包含处理当前请求的处理器对象和处理器链 getHandler(processedRequest)方法；

HandlerExecutionChain处理器链包括handler和拦截器数组，处理器链类结构：

public class HandlerExecutionChain {
    
    

	private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
	// 处理器对象
	private final Object handler;
	// 拦截器数组
	@Nullable
	private HandlerInterceptor[] interceptors;

	@Nullable
	private List<HandlerInterceptor> interceptorList;

	private int interceptorIndex = -1;
   
   //...省略若干方法

}

DIspatcherServlet的getHandler(processedRequest)方法

DIspatcherServlet.class
//处理器映射器集合
private List<HandlerMapping> handlerMappings;
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    
    
		if (this.handlerMappings != null) {
    
    
			for (HandlerMapping mapping : this.handlerMappings) {
    
    
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
    
    
					return handler;
				}
			}
		}
		return null;
	}

在这里插入图片描述
HandlerMapping为处理器映射器，用于缓存和获取url对应的处理器和拦截器。
private List handlerMappings; 为处理器映射器集合，目前有两种实现1.BeanNameURLHandlerMapping用于保存在标签里配置的url与Handler和Interceptor之间的映射关系，目前基本不用了；2.RequestMappingHandlerMapping用于保存通过@RequestMapping注解配置的url与Handler和Interceptor之间的映射关系，目前主流。
下面进入AbstractHandlerMapping#getHandler

AbstractHandlerMapping.java
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    
    
		// 匹配handler
		Object handler = getHandlerInternal(request);
		if (handler == null) {
    
    
			handler = getDefaultHandler();
		}
		if (handler == null) {
    
    
			return null;
		}
		// Bean name or resolved handler?
		if (handler instanceof String) {
    
    
			String handlerName = (String) handler;
			handler = obtainApplicationContext().getBean(handlerName);
		}
		// 匹配拦截器数组，将获取到的拦截器数组+handler封装到HandlerExecutionChain处理器链对象中
		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

		if (logger.isTraceEnabled()) {
    
    
			logger.trace("Mapped to " + handler);
		}
		else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) {
    
    
			logger.debug("Mapped to " + executionChain.getHandler());
		}

		if (CorsUtils.isCorsRequest(request)) {
    
    
			CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request);
			CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
			CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
			executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
		}

		return executionChain;
	}

2.根据handler链中的handler处理器获取对应的HandlerAdapter处理器适配器getHandlerAdapter(mappedHandler.getHandler());

由于handler的格式不固定有可能是实现Controller接口的类，有可能是标记@RequestMapping的方法，所以不同的handler要对应不同适配器来执行handler业务逻辑，HandlerAdapter可以理解为利用反射机制执行handler逻辑的反射工具类。

DIspatcherServlet.class
// 处理器适配器集合
private List<HandlerAdapter> handlerAdapters;
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
    
    
		if (this.handlerAdapters != null) {
    
    
			for (HandlerAdapter adapter : this.handlerAdapters) {
    
    
				if (adapter.supports(handler)) {
    
    
					return adapter;
				}
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}

在这里插入图片描述
根据handler在private List handlerAdapters;处理器集合中选择合适的适配器
SpringMVC中自带了三个处理器适配器:

HttpRequestHandlerAdapter，处理实现了HttpRequestHandler接口的handler

public boolean supports(Object handler) {
    
    
		return (handler instanceof HttpRequestHandler);
	}

SimpleControllerHandlerAdapter，处理实现了Controller接口的handler

public boolean supports(Object handler) {
    
    
		return (handler instanceof Controller);
	}

RequestMappingHandlerAdapter，处理被@RequestMapping注解标注的方法handler

public final boolean supports(Object handler) {
    
    
		return (handler instanceof HandlerMethod && supportsInternal((HandlerMethod) handler));
	}

3.依次执行handler链中拦截器数组中拦截器的preHandler方法，返回true继续执行，false直接return； mappedHandler.applyPreHandle(processedRequest, response)

此处会遍历拦截器数组中全部连接器，并且一次执行其preHandler方法，由此可见拦截器的preHandler在handler逻辑之前执行，可在拦截器的preHandler方法中进行权限验证等操作。

HandlerExecutionChain.class
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    
		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
    
    
			for (int i = 0; i < interceptors.length; i++) {
    
    
				HandlerInterceptor interceptor = interceptors[i];
				// 调用拦截器的preHandler方法
				if (!interceptor.preHandle(request, response, this.handler)) {
    
    
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

4.使用刚刚获取的HandlerAdapter处理器适配器执行handler逻辑，返回ModelAndView对象。mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

a.进入ha.handle

AbstractHandlerMethodAdapter.java
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
    
    

		return handleInternal(request, response, (HandlerMethod) handler);
	}

b.进入handleInternal

RequestMappingHandlerAdapter.java
protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    
    

		ModelAndView mav;
		checkRequest(request);

		// Execute invokeHandlerMethod in synchronized block if required.
		// 判断当前是否需要支持同一个session线性处理请求，保证session线程安全（可配置）
		if (this.synchronizeOnSession) {
    
    
			// 获取当前请求的session对象，如果尚未创建返回null。（如果getSession(true)是如尚未创建则会创建新session）
			HttpSession session = request.getSession(false);
			if (session != null) {
    
    
				// 根据session获取唯一key进行加锁
				Object mutex = WebUtils.getSessionMutex(session);
				synchronized (mutex) {
    
    
					// handler处理核心逻辑
					mav = invokeHandlerMethod(request, response, handlerMethod);
				}
			}
			else {
    
    
				// No HttpSession available -> no mutex necessary
				// session=null时
				// handler处理核心逻辑
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		}
		else {
    
    
			// No synchronization on session demanded at all...
			// session可以请求并行处理时
			// handler处理核心逻辑
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}

		if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
    
    
			if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
    
    
				applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
			}
			else {
    
    
				prepareResponse(response);
			}
		}

		return mav;
	}

c.进入invokeHandlerMethod

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
    
    

		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		try {
    
    
			WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
			ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

			ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
			if (this.argumentResolvers != null) {
    
    
				invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
			}
			if (this.returnValueHandlers != null) {
    
    
				invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
			}
			invocableMethod.setDataBinderFactory(binderFactory);
			invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
			// 封装ModelAndView容器
			ModelAndViewContainer mavContainer = new ModelAndViewContainer();
			mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
			modelFactory.initModel(webRequest, mavContainer, invocableMethod);
			mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

			AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
			asyncWebRequest.setTimeout(this.asyncRequestTimeout);

			WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
			asyncManager.setTaskExecutor(this.taskExecutor);
			asyncManager.setAsyncWebRequest(asyncWebRequest);
			asyncManager.registerCallableInterceptors(this.callableInterceptors);
			asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

			if (asyncManager.hasConcurrentResult()) {
    
    
				Object result = asyncManager.getConcurrentResult();
				mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
				asyncManager.clearConcurrentResult();
				LogFormatUtils.traceDebug(logger, traceOn -> {
    
    
					String formatted = LogFormatUtils.formatValue(result, !traceOn);
					return "Resume with async result [" + formatted + "]";
				});
				invocableMethod = invocableMethod.wrapConcurrentResult(result);
			}
			// handler核心处理逻辑
			invocableMethod.invokeAndHandle(webRequest, mavContainer);
			if (asyncManager.isConcurrentHandlingStarted()) {
    
    
				return null;
			}
			// 获取ModelAndView对象
			return getModelAndView(mavContainer, modelFactory, webRequest);
		}
		finally {
    
    
			webRequest.requestCompleted();
		}
	}

d.进入invokeAndHandle

ServletInvocableHandlerMethod.class
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
    
    
		// handler执行核心逻辑
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
    
    
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
    
    
				disableContentCachingIfNecessary(webRequest);
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
    
    
			mavContainer.setRequestHandled(true);
			return;
		}

		mavContainer.setRequestHandled(false);
		Assert.state(this.returnValueHandlers != null, "No return value handlers");
		try {
    
    
			// 获取结果处理器，处理handler返回值，保存到ModelAndView容器中。
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
    
    
			if (logger.isTraceEnabled()) {
    
    
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

e.进入invokeForRequest

InvocableHandlerMethod.class
public Object invokeForRequest(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
    
    
		// 获取handler1执行所需参数
		Object[] args = getMethodArgumentValues(request, mavContainer, providedArgs);
		if (logger.isTraceEnabled()) {
    
    
			logger.trace("Arguments: " + Arrays.toString(args));
		}
		// 反射调用handler方法，执行handler中的逻辑
		return doInvoke(args);
	}

f.进入getMethodArgumentValues

protected Object[] getMethodArgumentValues(NativeWebRequest request, @Nullable ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
    
    
		// 获取当前handler方法的形参
		MethodParameter[] parameters = getMethodParameters();
		if (ObjectUtils.isEmpty(parameters)) {
    
    
			return EMPTY_ARGS;
		}
		// 创建新数组，用于封装handler被调用时的实参（不同类型的形参获取方式不一样）
		Object[] args = new Object[parameters.length];
		// 遍历形参
		for (int i = 0; i < parameters.length; i++) {
    
    
			MethodParameter parameter = parameters[i];
			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
			args[i] = findProvidedArgument(parameter, providedArgs);
			if (args[i] != null) {
    
    
				continue;
			}
			if (!this.resolvers.supportsParameter(parameter)) {
    
    
				throw new IllegalStateException(formatArgumentError(parameter, "No suitable resolver"));
			}
			try {
    
    
				// 根据形参获取实参
				args[i] = this.resolvers.resolveArgument(parameter, mavContainer, request, this.dataBinderFactory);
			}
			catch (Exception ex) {
    
    
				// Leave stack trace for later, exception may actually be resolved and handled...
				if (logger.isDebugEnabled()) {
    
    
					String exMsg = ex.getMessage();
					if (exMsg != null && !exMsg.contains(parameter.getExecutable().toGenericString())) {
    
    
						logger.debug(formatArgumentError(parameter, exMsg));
					}
				}
				throw ex;
			}
		}
		return args;
	}

g.进入resolveArgument

HandlerMethodArgumentResolverComposite.class
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
    
    
		// 根据不同类型的参数获取不同的参数解析器。如：String的参数解析器AbstractNamedValueMethodArgumentResolver、Map的参数解析器MapMethodProcessor等
		HandlerMethodArgumentResolver resolver = getArgumentResolver(parameter);
		if (resolver == null) {
    
    
			throw new IllegalArgumentException("Unsupported parameter type [" +
					parameter.getParameterType().getName() + "]. supportsParameter should be called first.");
		}
		// 利用对应的参数解析器解析形参获取实参
		return resolver.resolveArgument(parameter, mavContainer, webRequest, binderFactory);
	}

此处以String的参数解析器AbstractNamedValueMethodArgumentResolver、Map的参数解析器MapMethodProcessor为例
h1.String的参数解析器AbstractNamedValueMethodArgumentResolver#resolveArgument里最终执行的是根据形参名称分别在请求头、请求Param中获取对应名称的参数
h2.Map的参数解析器MapMethodProcessor

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
    
    

		Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
		// 直接返回ModelAndView容器中的Model作为实参，此处也可以解释：在方法中声明形参Map，Model，ModelMap  并向里面填充的内容都会被写到请求域中
		return mavContainer.getModel();
	}

i.拿到handler执行的实参后回到第e步的doInvoke(args)，反射调用handler方法

InvocableHandlerMethod.class
protected Object doInvoke(Object... args) throws Exception {
    
    
		ReflectionUtils.makeAccessible(getBridgedMethod());
		try {
    
    
			// 反射调用执行handler方法
			return getBridgedMethod().invoke(getBean(), args);
		}
		catch (IllegalArgumentException ex) {
    
    
			assertTargetBean(getBridgedMethod(), getBean(), args);
			String text = (ex.getMessage() != null ? ex.getMessage() : "Illegal argument");
			throw new IllegalStateException(formatInvokeError(text, args), ex);
		}
		catch (InvocationTargetException ex) {
    
    
			// Unwrap for HandlerExceptionResolvers ...
			Throwable targetException = ex.getTargetException();
			if (targetException instanceof RuntimeException) {
    
    
				throw (RuntimeException) targetException;
			}
			else if (targetException instanceof Error) {
    
    
				throw (Error) targetException;
			}
			else if (targetException instanceof Exception) {
    
    
				throw (Exception) targetException;
			}
			else {
    
    
				throw new IllegalStateException(formatInvokeError("Invocation failure", args), targetException);
			}
		}
	}

j.到此handler方法以执行完毕，下面应处理handler返回值，保存到ModelAndView容器中，回到步骤d的this.returnValueHandlers.handleReturnValue()方法

HandlerMethodReturnValueHandlerComposite.class
public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
    
    
		// 根据不同结果类型获取不同的结果处理器如：String类型的结果处理器ViewNameMethodReturnValueHandler、ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler
		HandlerMethodReturnValueHandler handler = selectHandler(returnValue, returnType);
		if (handler == null) {
    
    
			throw new IllegalArgumentException("Unknown return value type: " + returnType.getParameterType().getName());
		}
		// 调用结果处理器完成handler返回值与ModelAndViewContainer的关系组装
		handler.handleReturnValue(returnValue, returnType, mavContainer, webRequest);
	}

此处以String类型的结果处理器ViewNameMethodReturnValueHandler、ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler为例子
k1.String类型的结果处理器ViewNameMethodReturnValueHandler#handleReturnValue

public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {
    
    
		// 如果返回值是String时，将返回值作为逻辑视图保存到ModelAndViewContainer中的view里
		if (returnValue instanceof CharSequence) {
    
    
			String viewName = returnValue.toString();
			mavContainer.setViewName(viewName);
			// 返回值是否包含重定向关键字，如果包含设置RedirectModelScenario=true在视图渲染时会用到
			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());
		}
	}

k2.ModelAndView类型的结果处理器ModelAndViewMethodReturnValueHandler#handleReturnValue
当返回值是在handler中new ModelAndView时此处会与形参中的Map，Model等合并返回作为新的Model封装到容器中

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

		if (returnValue == null) {
    
    
			mavContainer.setRequestHandled(true);
			return;
		}

		ModelAndView mav = (ModelAndView) returnValue;
		if (mav.isReference()) {
    
    
			String viewName = mav.getViewName();
			mavContainer.setViewName(viewName);
			if (viewName != null && isRedirectViewName(viewName)) {
    
    
				mavContainer.setRedirectModelScenario(true);
			}
		}
		else {
    
    
			View view = mav.getView();
			mavContainer.setView(view);
			if (view instanceof SmartView && ((SmartView) view).isRedirectView()) {
    
    
				mavContainer.setRedirectModelScenario(true);
			}
		}
		mavContainer.setStatus(mav.getStatus());
		// 当返回值是在handler中new ModelAndView时此处会与形参中的Map，Model等合并返回作为新的Model封装到容器中
		mavContainer.addAllAttributes(mav.getModel());
	}

l.到此handler的结果值以封装到ModelAndView容器ModelAndViewContainer中回到步骤c的 getModelAndView(mavContainer, modelFactory, webRequest);方法中，获取ModeAndView对象并返回

private ModelAndView getModelAndView(ModelAndViewContainer mavContainer,
			ModelFactory modelFactory, NativeWebRequest webRequest) throws Exception {
    
    

		modelFactory.updateModel(webRequest, mavContainer);
		if (mavContainer.isRequestHandled()) {
    
    
			return null;
		}
		ModelMap model = mavContainer.getModel();
		ModelAndView mav = new ModelAndView(mavContainer.getViewName(), model, mavContainer.getStatus());
		if (!mavContainer.isViewReference()) {
    
    
			mav.setView((View) mavContainer.getView());
		}
		if (model instanceof RedirectAttributes) {
    
    
			Map<String, ?> flashAttributes = ((RedirectAttributes) model).getFlashAttributes();
			HttpServletRequest request = webRequest.getNativeRequest(HttpServletRequest.class);
			if (request != null) {
    
    
				RequestContextUtils.getOutputFlashMap(request).putAll(flashAttributes);
			}
		}
		return mav;
	}

5.结果视图对象处理（如果未指定view逻辑视图名则根据请求路径给一个默认的逻辑视图名称）applyDefaultViewName(processedRequest, mv);

进入applyDefaultViewName

DIspatcherServlet.class
private void applyDefaultViewName(HttpServletRequest request, @Nullable ModelAndView mv) throws Exception {
    
    
		if (mv != null && !mv.hasView()) {
    
    
			// 在请求中根据url获取默认视图名称
			String defaultViewName = getDefaultViewName(request);
			if (defaultViewName != null) {
    
    
				mv.setViewName(defaultViewName);
			}
		}
	}

进入getDefaultViewName

//默认视图名转换器组件 DefaultRequestToViewNameTranslator (SpringMVC9大组件之一)
DIspatcherServlet.class
private RequestToViewNameTranslator viewNameTranslator;
protected String getDefaultViewName(HttpServletRequest request) throws Exception {
    
    
		// 如果初始化了默认视图名转换器组件则
		return (this.viewNameTranslator != null ? this.viewNameTranslator.getViewName(request) : null);
	}

进入getViewName
在这里插入图片描述

6.依次执行handler链中拦截器数组中拦截器的postHandle方法mappedHandler.applyPostHandle(processedRequest, response, mv);

此处会遍历拦截器数组中全部连接器，并且一次执行其postHandle方法，由此可见拦截器的postHandle在handler逻辑之后，视图渲染之前执行，可在拦截器的postHandle方法中对ModelAndView值进行修改。
进入applyPostHandle方法

HandlerExecutionChain.class
public void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {
    
    

		HandlerInterceptor[] interceptors = getInterceptors();
		if (!ObjectUtils.isEmpty(interceptors)) {
    
    
			for (int i = interceptors.length - 1; i >= 0; i--) {
    
    
				HandlerInterceptor interceptor = interceptors[i];
				// 循环调用拦截器的postHandler方法
				interceptor.postHandle(request, response, this.handler, mv);
			}
		}
	}

7.数据模型model封装到请求域中并请求转发到真正的视图进行视图渲染processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);

进入a.processDispatchResult

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {
    
    

		boolean errorView = false;

		if (exception != null) {
    
    
			if (exception instanceof ModelAndViewDefiningException) {
    
    
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = ((ModelAndViewDefiningException) exception).getModelAndView();
			}
			else {
    
    
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(request, response, handler, exception);
				errorView = (mv != null);
			}
		}

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
    
    
			// 视图渲染核心方法
			render(mv, request, response);
			if (errorView) {
    
    
				WebUtils.clearErrorRequestAttributes(request);
			}
		}
		else {
    
    
			if (logger.isTraceEnabled()) {
    
    
				logger.trace("No view rendering, null ModelAndView returned.");
			}
		}

		if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
    
    
			// Concurrent handling started during a forward
			return;
		}

		if (mappedHandler != null) {
    
    
			//8.当页面渲染请求转发后无异常时也会依次执行handler链中拦截器数组中拦截器的afterCompletion方法
			//afterCompletion方法在⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)
			mappedHandler.triggerAfterCompletion(request, response, null);
		}
	}

b.进入render

protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    
		// Determine locale for request and apply it to the response.
		Locale locale =
				(this.localeResolver != null ? this.localeResolver.resolveLocale(request) : request.getLocale());
		response.setLocale(locale);

		View view;
		String viewName = mv.getViewName();
		if (viewName != null) {
    
    
			// We need to resolve the view name.
			// 根据逻辑视图名解析封装实际视图
			view = resolveViewName(viewName, mv.getModelInternal(), locale, request);
			if (view == null) {
    
    
				throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
						"' in servlet with name '" + getServletName() + "'");
			}
		}
		else {
    
    
			// No need to lookup: the ModelAndView object contains the actual View object.
			view = mv.getView();
			if (view == null) {
    
    
				throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
						"View object in servlet with name '" + getServletName() + "'");
			}
		}

		// Delegate to the View object for rendering.
		if (logger.isTraceEnabled()) {
    
    
			logger.trace("Rendering view [" + view + "] ");
		}
		try {
    
    
			if (mv.getStatus() != null) {
    
    
				response.setStatus(mv.getStatus().value());
			}
			// 请求域数据封装，视图跳转（RedirectView重定向，AbstractUrlBasedView请求转发）
			view.render(mv.getModelInternal(), request, response);
		}
		catch (Exception ex) {
    
    
			if (logger.isDebugEnabled()) {
    
    
				logger.debug("Error rendering view [" + view + "]", ex);
			}
			throw ex;
		}
	}

c.进入resolveViewName，View是个接口，根据不同的逻辑视图名称，会创建出不同的View实现

DIspatcherServlet.class
//  视图解析器SpringMVC的九大组件之一需在xml中配置InternalResourceViewResolver（extends UrlBasedViewResolver），主要作用设置视图前缀后缀
private List<ViewResolver> viewResolvers;
protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
			Locale locale, HttpServletRequest request) throws Exception {
    
    

		if (this.viewResolvers != null) {
    
    
			// 遍历视图解析器，找到合适的视图解析器解析视图
			for (ViewResolver viewResolver : this.viewResolvers) {
    
    
				View view = viewResolver.resolveViewName(viewName, locale);
				if (view != null) {
    
    
					return view;
				}
			}
		}
		return null;
	}

d.进入resolveViewName

AbstractCachingViewResolver.class
public View resolveViewName(String viewName, Locale locale) throws Exception {
    
    
		if (!isCache()) {
    
    
			return createView(viewName, locale);
		}
		else {
    
    
			// 默认开启视图缓存机制，视图渲染跳转过一次后会进行缓存
			Object cacheKey = getCacheKey(viewName, locale);
			View view = this.viewAccessCache.get(cacheKey);

			if (view == null) {
    
    
				// 如果缓存中不存在该视图
				synchronized (this.viewCreationCache) {
    
    
					// 防止并发不安全锁内再判断一边
					view = this.viewCreationCache.get(cacheKey);
					if (view == null) {
    
    
						// Ask the subclass to create the View object.
						// 创建视图核心逻辑
						view = createView(viewName, locale);
						if (view == null && this.cacheUnresolved) {
    
    
							view = UNRESOLVED_VIEW;
						}
						if (view != null) {
    
    
							this.viewAccessCache.put(cacheKey, view);
							this.viewCreationCache.put(cacheKey, view);
						}
					}
				}
			}
			else {
    
    
				if (logger.isTraceEnabled()) {
    
    
					logger.trace(formatKey(cacheKey) + "served from cache");
				}
			}
			return (view != UNRESOLVED_VIEW ? view : null);
		}
	}

e.进入createView，根据逻辑视图名中不同的关键字获取不同类型的View实现如包含关键字"redirect:"创建RedirectView，包含关键字"forward"创建关键字InternalResourceView

protected View createView(String viewName, Locale locale) throws Exception {
    
    
		// If this resolver is not supposed to handle the given view,
		// return null to pass on to the next resolver in the chain.
		if (!canHandle(viewName, locale)) {
    
    
			return null;
		}

		// Check for special "redirect:" prefix.
		// 判断是否包含重定向关键字
		if (viewName.startsWith(REDIRECT_URL_PREFIX)) {
    
    
			String redirectUrl = viewName.substring(REDIRECT_URL_PREFIX.length());
			// 封装重定向视图
			RedirectView view = new RedirectView(redirectUrl,
					isRedirectContextRelative(), isRedirectHttp10Compatible());
			String[] hosts = getRedirectHosts();
			if (hosts != null) {
    
    
				view.setHosts(hosts);
			}
			// 将视图加载到Spring容器
			return applyLifecycleMethods(REDIRECT_URL_PREFIX, view);
		}

		// Check for special "forward:" prefix.
		// 判断是否包含请求转发关键字
		if (viewName.startsWith(FORWARD_URL_PREFIX)) {
    
    
			String forwardUrl = viewName.substring(FORWARD_URL_PREFIX.length());
			// 封装请求转发资源视图InternalResourceView extends AbstractUrlBasedView
			InternalResourceView view = new InternalResourceView(forwardUrl);
			// 将视图加载到Spring容器
			return applyLifecycleMethods(FORWARD_URL_PREFIX, view);
		}

		// Else fall back to superclass implementation: calling loadView.
		// 创建正常视图AbstractUrlBasedView（正常视图后面渲染流转也是走forward请求转发）
		return super.createView(viewName, locale);
	}

f.至此真正视图对象以获取，下面我们回到b步骤的view.render(mv.getModelInternal(), request, response);
请求域数据封装，视图跳转（RedirectView重定向，InternalResourceView请求转发）

AbstractView.class
public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {
    
    

		if (logger.isDebugEnabled()) {
    
    
			logger.debug("View " + formatViewName() +
					", model " + (model != null ? model : Collections.emptyMap()) +
					(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
		}
		// 合并model
		Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		// 准备响应设置参数
		prepareResponse(request, response);
		// 请求域数据封装+请求转发
		renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
	}

g1.进入RedirectView实现核心步骤RedirectView#renderMergedOutputModel
此处也解释了SpringMVC重定向请求数据传递的原理
在这里插入图片描述

RedirectView.class
protected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request,
			HttpServletResponse response) throws IOException {
    
    

		String targetUrl = createTargetUrl(model, request);
		targetUrl = updateTargetUrl(targetUrl, model, request, response);

		// Save flash attributes
		//向session中添加Flash属性用于重定向传递参数
		RequestContextUtils.saveOutputFlashMap(targetUrl, request, response);

		// Redirect
		// 完成重定向response.sendRedirect(encodedURL);
		sendRedirect(request, response, targetUrl, this.http10Compatible);
	}

g2.进入InternalResourceView实现核心步骤InternalResourceView#renderMergedOutputModel

protected void renderMergedOutputModel(
			Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {
    
    

		// Expose the model object as request attributes.
		// 将model中的数据封装到请求域里request.setAttribute(name, value);
		exposeModelAsRequestAttributes(model, request);

		// Expose helpers as request attributes, if any.
		exposeHelpers(request);

		// Determine the path for the request dispatcher.
		// 获取真实视图地址
		String dispatcherPath = prepareForRendering(request, response);

		// Obtain a RequestDispatcher for the target resource (typically a JSP).
		// 封装请求转发器javax.servlet.RequestDispatcher
		RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);
		if (rd == null) {
    
    
			throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +
					"]: Check that the corresponding file exists within your web application archive!");
		}

		// If already included or response already committed, perform include, else forward.
		if (useInclude(request, response)) {
    
    
			response.setContentType(getContentType());
			if (logger.isDebugEnabled()) {
    
    
				logger.debug("Including [" + getUrl() + "]");
			}
			// 注： 当前response是否已经设置了响应值，列入在某个拦截器或者Servlet中进行了处理，则会抛出异常，阻止当前跳转，响应之前设置的内容
			rd.include(request, response);
		}

		else {
    
    
			// Note: The forwarded resource is supposed to determine the content type itself.
			if (logger.isDebugEnabled()) {
    
    
				logger.debug("Forwarding to [" + getUrl() + "]");
			}
			// 请求转发
			rd.forward(request, response);
		}
	}

注：至此视图的渲染和跳转已完成，等待当前请求的全部方法栈执行完毕后，浏览器即可看到调转效果，这里特别提一下回到a的mappedHandler.triggerAfterCompletion(request, response, null);当视图渲染跳转过程中无异常时，最后也会执行一遍流程8，也就是遍历调用拦截器的afterCompletion方法，此时异常为null

8.依次执行handler链中拦截器数组中拦截器的afterCompletion方法⻚⾯已经跳转渲染完毕之后,响应到浏览器之前执⾏（用来捕获视图渲染时发生的异常)triggerAfterCompletion(processedRequest, response, mappedHandler, ex);

此处会遍历拦截器数组中全部连接器，并且一次执行其triggerAfterCompletion方法，由此可见拦截器的triggerAfterCompletion在视图渲染之后并且出现渲染异常时调用，可以在拦截器的triggerAfterCompletion方法中进行异常捕获。

总结SpringMVC处理请求的详细流程：

1.请求到达DispatcherServlet前端控制器，DispatcherServlet遍历处理器映射器HandlerMapping集合,根据请求的url匹配对应的处理器链HandlerExecutionChain包含一个Handler处理器和一个拦截器HandlerInterceptor[]数组。
2.DispatcherServlet遍历处理器适配器HandlerAdapter集合，根据处理器链中的Handler匹配对应的处理器适配器。
3.DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的preHandle方法（可在拦截器此方法中进行权限验证）
4.DispatcherServlet委派HandlerAdapter执行Handler业务方法，遍历handler的形参，根据不同的形参类型获取不同的HandlerMethodArgumentResolver参数解析器，调用参数解析器获取实参，获取实参后反射调用handler方法并保存方法returnValue返回值，根据返回值的类型获取对应的结果处理器，调用结果处理器将returnValue封装为ModelAndView返回DispatcherServlet.
5.检测ModelAndView中是否包含逻辑视图名称，如果逻辑视图名称为空则调用DefaultRequestToViewNameTranslator默认视图名称转换器获取默认逻辑视图名称。
6.DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的postHandle方法
7.DIspatcherServlet遍历ViewResolver视图解析器数组获取对应的视图解析器，根据逻辑视图名称获取不同类型的View视图实现如（重定向视图RedirectView、请求转发资源视图InternalResourceView），获取到视图后将model数据写入请求域，然后进行请求转发或者重定向处理跳转到视图进行渲染。
8.当视图渲染完成或者渲染中出错时DispatcherServlet遍历处理器链中的拦截器数组，执行每个拦截器的afterCompletion方法
9.当前请求的全部方法栈执行完毕后Tomcat将渲染好的视图响应给浏览器。

SpringMVC请求流程处理源码剖析（我斑愿称你为最全）已完善最后总结