org.springframework.web.servlet.DispatcherServlet-doDispatch 总体流程

doDispatch方法-总体流程

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		/**
		 * 声明变量 HttpServletRequest HandlerExecutionChain Handler执行链包含和最扣执行的Handler
		 */
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		//是不是一个多组件请求
		boolean multipartRequestParsed = false;
		//异步管理器
		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

		try {
			//视图
			ModelAndView mv = null;
			//异常
			Exception dispatchException = null;

			try {
				/**
				 * 1.检查是否上传请求
				 */
				processedRequest = checkMultipart(request);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				/**
				 * 2.根据processedRequest获取映射的Handler执行链 HandlerExecutionChain
				 * 有当前请求的Handler和Inteceptor
				 */
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					/**
					 * 如果mappedHandler为空就返回404
					 */
					noHandlerFound(processedRequest, response);
					return;
				}

				/**
				 * 3.根据mappedHandler  HandlerExecutionChain  HandlerAdapter适配器
				 */
				// Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				/**
				 * 获取请求方法
				 * 处理last-modified 请求头
				 */
				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = "GET".equals(method);
				if (isGet || "HEAD".equals(method)) {
					//获取最近修改时间,缓存
					long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
					if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
						return;
					}
				}

				/**
				 * 4.预处理,行执行拦截器等
				 */
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				/**
				 * 5.实现执行Controller中(Handler)的方法,返回ModelAndView视图
				 */
				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					/**
					 * 判断 是不是异步请求,是就返回了
					 */
					return;
				}
				/**
				 * 6对象视图对象的处理
				 */
				applyDefaultViewName(processedRequest, mv);
				/**
				 * 7.拦截器后后置处理
				 */
				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);
			}
			/**
			 * 8对页面渲染
			 */
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			/**
			 * 9对页面渲染完成里调用拦截器中的AfterCompletion方法
			 */
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			/**
			 * 最终对页面渲染完成里调用拦截器中的AfterCompletion方法
			 */
			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);
				}
			}
		}
	}