springmvc学习一

//前端控制器分派方法
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HttpServletRequest processedRequest = request;
		HandlerExecutionChain mappedHandler = null;
		int interceptorIndex = -1;

		try {
			ModelAndView mv;
			boolean errorView = false;

			try {
                   //检查是否是请求是否是multipart（如文件上传），如果是将通过MultipartResolver解析
				processedRequest = checkMultipart(request);
                   //步骤2、请求到处理器（页面控制器）的映射，通过HandlerMapping进行映射
				mappedHandler = getHandler(processedRequest, false);
				if (mappedHandler == null || mappedHandler.getHandler() == null) {
					noHandlerFound(processedRequest, response);
					return;
				}
                   //步骤3、处理器适配，即将我们的处理器包装成相应的适配器（从而支持多种类型的处理器）
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                  // 304 Not Modified缓存支持
			    //此处省略具体代码

				// 执行处理器相关的拦截器的预处理（HandlerInterceptor.preHandle）
				//此处省略具体代码

				// 步骤4、由适配器执行处理器（调用处理器相应功能处理方法）
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				// Do we need view name translation?
				if (mv != null && !mv.hasView()) {
					mv.setViewName(getDefaultViewName(request));
				}

				// 执行处理器相关的拦截器的后处理（HandlerInterceptor.postHandle）
				//此处省略具体代码
			}
			catch (ModelAndViewDefiningException ex) {
				logger.debug("ModelAndViewDefiningException encountered", ex);
				mv = ex.getModelAndView();
			}
			catch (Exception ex) {
				Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
				mv = processHandlerException(processedRequest, response, handler, ex);
				errorView = (mv != null);
			}

			//步骤5 步骤6、解析视图并进行视图的渲染
//步骤5 由ViewResolver解析View（viewResolver.resolveViewName(viewName, locale)）
//步骤6 视图在渲染时会把Model传入（view.render(mv.getModelInternal(), request, response);）
			if (mv != null && !mv.wasCleared()) {
				render(mv, processedRequest, response);
				if (errorView) {
					WebUtils.clearErrorRequestAttributes(request);
				}
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
							"': assuming HandlerAdapter completed request handling");
				}
			}

			// 执行处理器相关的拦截器的完成后处理（HandlerInterceptor.afterCompletion）
			//此处省略具体代码


		catch (Exception ex) {
			// Trigger after-completion for thrown exception.
			triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
			throw ex;
		}
		catch (Error err) {
			ServletException ex = new NestedServletException("Handler processing failed", err);
			// Trigger after-completion for thrown exception.
			triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
			throw ex;
		}

		finally {
			// Clean up any resources used by a multipart request.
			if (processedRequest != request) {
				cleanupMultipart(processedRequest);
			}
		}
	}