SpringMVC 拦截器源码解析

前言：这两天学习了代理模式，自然想到了SpringMVC 的 AOP 使用的就是动态代理，拦截器使用的就是 jdk 的动态代理。今天看了看源码，记录一下。SpringMVC 的拦截器使用移步：Java Servlet 过滤器与 SpringMVC 拦截器的区别？

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);

try {
            this.doDispatch(request, response);
        } finally {
            if(!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted() && attributesSnapshot != null) {
                this.restoreAttributesAfterInclude(request, attributesSnapshot);
            }

}

}

　　doService() 方法里面处理了一些信息之后，调用了 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 {
            try {
                ModelAndView mv = null;
                Object dispatchException = null;

try {
                    processedRequest = this.checkMultipart(request);
                    multipartRequestParsed = processedRequest != request;
                    mappedHandler = this.getHandler(processedRequest);
                    if(mappedHandler == null || mappedHandler.getHandler() == null) {
                        this.noHandlerFound(processedRequest, response);
                        return;
                    }