SpringMVC请求流程处理源码剖析

pringMVC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

1. 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）
2. HandlerMapping根据请求的url获取对应的handler给到DispatcherServlet
3. 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
4. handler执行后返回ModelAndView给DispatcherServlet
5. 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
6. 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
7. 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）

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);
				}
			}
		}
	}

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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

}

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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;
	}

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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;
	}

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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");
	}

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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:

1. HttpRequestHandlerAdapter，处理实现了HttpRequestHandler接口的handler

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

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1. SimpleControllerHandlerAdapter，处理实现了Controller接口的handler

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

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1. 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));
	}

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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;
	}

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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);
	}

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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;
	}

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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();
		}
	}

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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;
		}
	}

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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);
	}

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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;
	}

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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);
	}

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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();
	}

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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);
			}
		}
	}

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