Java spring mvc请求详情介绍

/**
 * 最核心的控制器
 * 源码位置：org.springframework.web.servlet.DispatcherServlet.doDispatch(HttpServletRequest, HttpServletResponse)
 */
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
	HttpServletRequest processedRequest = request;
	HandlerExecutionChain mappedHandler = null;
	boolean multipartRequestParsed = false;

	WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

		try {
			// 验证是不是上传的请求，上传的请求会转化为MultipartHttpServletRequest
			processedRequest = checkMultipart(request);
			multipartRequestParsed = (processedRequest != request);

			// 进行映射
			mappedHandler = getHandler(processedRequest);
			if (mappedHandler == null) {
				noHandlerFound(processedRequest, response);
				return;
			}

			// 找到最合适的HandlerAdapter，按照顺序，那个先解析到就是那个
			HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

			// Process last-modified header, if supported by the handler.  HTTP缓存相关
			String method = request.getMethod();
			boolean isGet = HttpMethod.GET.matches(method);
			if (isGet || HttpMethod.HEAD.matches(method)) {
				long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
				if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
					return;
				}
			}
			// 前置拦截器
			if (!mappedHandler.applyPreHandle(processedRequest, response)) {
				// 返回false就不进行后续处理了
				return;
			}

			// Actually invoke the handler.
			// 获取参数，执行方法
			mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

			if (asyncManager.isConcurrentHandlingStarted()) {
				return;
			}
			// 如果mv有  视图没有，给你设置默认视图
			applyDefaultViewName(processedRequest, mv);
			//后置拦截器
			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);
		}
		// 渲染视图
		processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
	}
	catch (Exception ex) {
		triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
	}
	catch (Throwable err) {
		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);
			}
		}
	}
}

/**
 * 获取处理器映射器
 * 源码位置：org.springframework.web.servlet.DispatcherServlet.getHandler(HttpServletRequest)
 */
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
	if (this.handlerMappings != null) {
		/** 拿到所有handlerMappings （容器启动阶段初始化：拿到所有实现了HandlerMapping的Bean）
		 * @see DispatcherServlet#initHandlerMappings
		 * 测试发现： 不同的HandlerMapping可以有相同path, 谁先解析到就用哪个
		 * */
		for (HandlerMapping mapping : this.handlerMappings) {
			HandlerExecutionChain handler = mapping.getHandler(request);
			if (handler != null) {
				return handler;
			}
		}
	}
	return null;
}

/**
 * 获取处理器适配器
 * 源码位置：org.springframework.web.servlet.DispatcherServlet.getHandlerAdapter(Object)
 */
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
	if (this.handlerAdapters != null) {
		// 按照配置的顺序，谁先解析到就用那个
		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");
}

/**
 * 获取参数，执行方法最外层的调用
 * 源码位置：org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(HttpServletRequest, HttpServletResponse, Object)
 */
public final ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
		throws Exception {
	// 直接调用这个方法
	return handleInternal(request, response, (HandlerMethod) handler);
}

/**
 * 获取参数，执行方法内部的调用逻辑
 * 源码位置：org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(HttpServletRequest, HttpServletResponse, HandlerMethod)
 */
protected ModelAndView handleInternal(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

	ModelAndView mav;
	// 检查当前请求的method是否为支持的method(默认Null,可通过继承AbstractController设置supportedMethods)
	// 检查当前请求是否必须session  (默认false,可通过继承AbstractController设置requireSession)
	checkRequest(request);

	/**
	 * 判断当前是否需要支持在同一个session中只能线性地处理请求：一个session同时只能处理一个线程
	 * 因为锁是通过 synchronized 是 JVM 进程级，所以在分布式环境下，
	 * 无法达到同步相同 Session 的功能。默认情况下，synchronizeOnSession 为 false
	 */
	if (this.synchronizeOnSession) {
		// 获取当前请求的session对象
		HttpSession session = request.getSession(false);
		if (session != null) {
			// 为当前session生成一个唯一的可以用于锁定的key
			Object mutex = WebUtils.getSessionMutex(session);
			synchronized (mutex) {
				// 对HandlerMethod进行参数等的适配处理，并调用目标handler
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		}
		else {
			// 如果当前不存在session，则直接对HandlerMethod进行适配
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}
	}
	else {
		// *如果当前不需要对session进行同步处理，则直接对HandlerMethod进行适配
		mav = invokeHandlerMethod(request, response, handlerMethod);
	}


	//判断当前请求头中是否包含Cache-Control请求头，如果不包含，则对当前response进行处理
	if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
		// 如果当前SessionAttribute中存在配置的attributes，则为其设置过期时间。
		// 这里SessionAttribute主要是通过@SessionAttribute注解生成的
		if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
			applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
		}
		else {
			// 如果当前不存在SessionAttributes，则判断当前是否存在Cache-Control设置，
			// 如果存在，则按照该设置进行response处理，如果不存在，则设置response中的
			// Cache的过期时间为-1，即立即失效
			prepareResponse(response);
		}
	}

	return mav;
}

/**
 * 获取参数，执行方法前的准备逻辑
 * 源码位置：org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(HttpServletRequest, HttpServletResponse, HandlerMethod)
 */
protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
		HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
	// 把我们的请求req resp包装成 ServletWebRequest
	ServletWebRequest webRequest = new ServletWebRequest(request, response);
	try {
		// 获取容器中全局配置的InitBinder和当前HandlerMethod所对应的Controller中
		// 配置的InitBinder，用于进行参数的绑定
		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);

		// 获取容器中全局配置的ModelAttribute和当前HandlerMethod所对应的Controller 中配置的ModelAttribute，
		// 这些配置的方法将会在目标方法调用之前进行调用
		ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

		// 封装handlerMethod，会在调用前解析参数、调用后对返回值进行处理
		ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
		if (this.argumentResolvers != null) {
			// 让invocableMethod拥有参数解析能力
			invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		}
		if (this.returnValueHandlers != null) {
			// 让invocableMethod拥有返回值处理能力
			invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
		}
		// 让invocableMethod拥有InitBinder解析能力
		invocableMethod.setDataBinderFactory(binderFactory);
		// 设置ParameterNameDiscoverer，该对象将按照一定的规则获取当前参数的名称
		invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
		// ModelAndView处理容器
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();
		// 将request的Attribute复制一份到ModelMap
		mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
		// *调用我们标注了@ModelAttribute的方法,主要是为我们的目标方法预加载
		modelFactory.initModel(webRequest, mavContainer, invocableMethod);
		// 重定向的时候，忽略model中的数据 默认false
		mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

		// 获取当前的AsyncWebRequest，这里AsyncWebRequest的主要作用是用于判断目标
		// handler的返回值是否为WebAsyncTask或DeferredResult，如果是这两种中的一种，
		// 则说明当前请求的处理应该是异步的。所谓的异步，指的是当前请求会将Controller中
		// 封装的业务逻辑放到一个线程池中进行调用，待该调用有返回结果之后再返回到response中。
		// 这种处理的优点在于用于请求分发的线程能够解放出来，从而处理更多的请求,提高吞吐。
		// 只有待目标任务完成之后才会回来将该异步任务的结果返回。
		AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
		asyncWebRequest.setTimeout(this.asyncRequestTimeout);
		// 封装异步任务的线程池、request、interceptors到WebAsyncManager中
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.setTaskExecutor(this.taskExecutor);
		asyncManager.setAsyncWebRequest(asyncWebRequest);
		asyncManager.registerCallableInterceptors(this.callableInterceptors);
		asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

		// 这里就是用于判断当前请求是否有异步任务结果的，如果存在，则对异步任务结果进行封装
		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);
		}
		// *对请求参数进行处理，调用目标HandlerMethod，并且将返回值封装为一个ModelAndView对象
		invocableMethod.invokeAndHandle(webRequest, mavContainer);
		if (asyncManager.isConcurrentHandlingStarted()) {
			return null;
		}

		// 对封装的ModelAndView进行处理，主要是判断当前请求是否进行了重定向，如果进行了重定向，
		// 还会判断是否需要将FlashAttributes封装到新的请求中
		return getModelAndView(mavContainer, modelFactory, webRequest);
	}
	finally {
		webRequest.requestCompleted();
	}
}

/**
 * 获取参数，执行方法
 * 源码位置：org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletWebRequest, ModelAndViewContainer, Object...)
 */
public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
		Object... providedArgs) throws Exception {

	/*真正的调用我们的目标对象 很重要 很重要*/
	Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
	// 设置相关的返回状态
	setResponseStatus(webRequest);
	// 如果请求处理完成，则设置requestHandled属性
	if (returnValue == null) {
		if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
			disableContentCachingIfNecessary(webRequest);
			mavContainer.setRequestHandled(true);
			return;
		}
	}
	// 如果请求失败，但是有错误原因，那么也会设置requestHandled属性
	else if (StringUtils.hasText(getResponseStatusReason())) {
		mavContainer.setRequestHandled(true);
		return;
	}

	mavContainer.setRequestHandled(false);
	Assert.state(this.returnValueHandlers != null, "No return value handlers");
	try {
		// 遍历当前容器中所有ReturnValueHandler，判断哪种handler支持当前返回值的处理，
		// 如果支持，则使用该handler处理该返回值
		this.returnValueHandlers.handleReturnValue(
				returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
	}
	catch (Exception ex) {
		if (logger.isTraceEnabled()) {
			logger.trace(formatErrorForReturnValue(returnValue), ex);
		}
		throw ex;
	}
}

/**
 * 渲染视图逻辑
 * 源码位置：org.springframework.web.servlet.DispatcherServlet.processDispatchResult(HttpServletRequest, HttpServletResponse, HandlerExecutionChain, ModelAndView, Exception)
 */
private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
		@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
		@Nullable Exception exception) throws Exception {

	boolean errorView = false;

	// 异常视图
	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()) {
		// 解析、渲染视图：解析视图名，拼接前后缀
		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) {
		// Exception (if any) is already handled..   拦截器：AfterCompletion
		mappedHandler.triggerAfterCompletion(request, response, null);
	}
}