SpringMVC流程解析学习【doDispatch】

流程概述

　所有请求经过DispatcherServlet
　调用doDispatch()进行处理
　　1.gerHandler()根据当前请求在HandlerMapping中找到请求的映射信息，找到能处理请求的目标处理器
　　2.getHandlerAdapter()根据获取到的处理器找到对应的HandlerAdapter(Spring3.1后使用RequestMappingHandlerAdapter代替Spring2.5中的AnnotationMethodHandlerAdapter)，执行目标方法
　　3.HandlerAdapter通过反射执行方法，返回一个 ModelAndView对象
　　4.processDispatchResult( ) 根据封装的ModelAndView转发到对应的页面，且ModelAndView中的数据可以由请求域中获取

gerHandler

　mappedHandler = getHandler(processedRequest);
　processedRequest得到请求地址

　HandlerMapping：handlerMap参数保存了请求对应的处理器(IOC启动扫描时保存)
遍历HandlerMapping，判断processedRequest中的请求由哪个Handler处理。

getHandlerAdapter

　HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler())

ModelAndView

mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

得到handler对应handlerAdapter后通过反射执行目标方法，返回ModelAndView对象

processDispatchResult

得到ModelAndView后，processDispatchResult()根据ModelAndView封装的信息转发到对应的页面

源码

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);
				multipartRequestParsed = (processedRequest != request);

				// Determine handler for the current request.
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
				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;
					}
				}

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

				// Actually invoke the handler.
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				if (asyncManager.isConcurrentHandlingStarted()) {
					return;
				}

				applyDefaultViewName(processedRequest, mv);
				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);
			}
			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);
				}
			}
		}
	}