源码解析

　　springMVC 的所有连接入口都会进入 DispatcherServlet，然后在这里面去调用真正的 Controller。而拦截器要达到的作用则是在调用 Controller 前后去做一些事情。所以现在需要看看 DispatcherServlet 的源码。

DispatcherServlet

　　DispatcherServlet 的源码入口在 doService() 方法。

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
        if(this.logger.isDebugEnabled()) {
            String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult()?" resumed":"";
            this.logger.debug("DispatcherServlet with name '" + this.getServletName() + "'" + resumed + " processing " + request.getMethod() + " request for [" + getRequestUri(request) + "]");
        }

        Map<String, Object> attributesSnapshot = null;
        if(WebUtils.isIncludeRequest(request)) {
            attributesSnapshot = new HashMap();
            Enumeration attrNames = request.getAttributeNames();

            label108:
            while(true) {
                String attrName;
                do {
                    if(!attrNames.hasMoreElements()) {
                        break label108;
                    }

                    attrName = (String)attrNames.nextElement();
                } while(!this.cleanupAfterInclude && !attrName.startsWith("org.springframework.web.servlet"));

                attributesSnapshot.put(attrName, request.getAttribute(attrName));
            }
        }

        request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, this.getWebApplicationContext());
        request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
        request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
        request.setAttribute(THEME_SOURCE_ATTRIBUTE, this.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);