SpringMVC-请求处理的大致流程分析---doDispatch( )细节

	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 {
				processedRequest = checkMultipart(request);//1.检查是否文件上传相关请求
				multipartRequestParsed = (processedRequest != request);
　　　　　　　　　　　　　　　　　　　　
				// Determine handler for the current request.2.根据当前请求，找到处理当前请求的处理器
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {　　//3.没找到就抛异常或发送错误页面 404
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
//　4.获取能执行这个类的所有方法的适配器（反射工具 AnnotationMethodHandlerAdapter)
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();//获取当前请求方式
				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;
					}
				}

				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				// Actually invoke the handler.
　　　　　　// 5.处理器的方法被调用了，适配器执行目标方法，返回一个 ModelAndView 对象 mv，返回页面自动装配在view属性里
　　　　　　//目标方法执行完成后的返回值作为视图名，设置保存到 ModelAndView 中，无论目标方法怎么写，最终适配器执行完成以后都会将执行后的信息封装成ModelAndView
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
　　　　　　　　　　　　　　
				if (asyncManager.isConcurrentHandlingStarted()) {　　//是否异步方法？
					return;
				}

				applyDefaultViewName(processedRequest, mv);　　//如果没有视图名，使用默认视图名
				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);
			}
//6.转发到目标页面，根据方法最终执行完成后封装的ModelAndView，转发到对应页面，而且ModelAndView中的数据可以从请求域中获取
			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);
				}
			}
		}
	}