springMVC系列源码之请求处理过程――12 - JAVA

equest中、然后交由doDispatch处理。FrameworkServlet中的doService()是抽象方法只是一个模版、具体的实现还是在DispatcherServlet中：

	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {

		if (logger.isDebugEnabled()) {
			String requestUri = urlPathHelper.getRequestUri(request);
			String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult()   " resumed" : "";
			logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +
					" processing " + request.getMethod() + " request for [" + requestUri + "]");
		}

		// Keep a snapshot of the request attributes in case of an include,
		// to be able to restore the original attributes after the include.
		Map
  
    attributesSnapshot = null;
		if (WebUtils.isIncludeRequest(request)) {
			logger.debug("Taking snapshot of request attributes before include");
			attributesSnapshot = new HashMap
   
    (); Enumeration
     attrNames = request.getAttributeNames(); while (attrNames.hasMoreElements()) { String attrName = (String) attrNames.nextElement(); if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) { attributesSnapshot.put(attrName, request.getAttribute(attrName)); } } } // Make framework objects available to handlers and view objects. request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext()); request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver); request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver); request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource()); FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response); if (inputFlashMap != null) { request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap)); } request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap()); request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager); try { doDispatch(request, response); } finally { if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { return; } // Restore the original attribute snapshot, in case of an include. if (attributesSnapshot != null) { restoreAttributesAfterInclude(request, attributesSnapshot); } } }

关键部分是几个requet.setAttribute()方法的调用，将前面在初始化流程中实例化的对象设置到http请求的属性中，供下一步处理使用，其中有容器的上下文对象、本地化解析器等SpringMVC特有的编程元素。不同于Struts2中的ValueStack，SpringMVC的数据并没有从HttpServletRequest对象中抽离出来再存进另外一个编程元素，这也跟SpringMVC的设计思想有关。因为从一开始，SpringMVC的设计者就认为，不应该将请求处理过程和Web容器完全隔离。

所以，你可以看到，真正发生请求转发的方法doDispatch()中，它的参数是HttpServletRequest和HttpServletResponse对象。这给我们传递的意思也很明确，从request中能获取到一切请求的数据，从response中，我们又可以往服务器端输出任何响应，Http请求的处理，就应该围绕这两个对象来设计。我们不妨可以将SpringMVC这种设计方案，是从Struts2的过度设计中吸取教训，而向Servlet编程的一种回归和简化。

2.3 doDispatch方法：

	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 = processedReque

springMVC系列源码之请求处理过程――12(二)