SpringMVC 处理器执行链 （HandlerMapping）的执行过程

第一步：在web.xml中找到DispatcherServlet，然后ctrl+鼠标左键进入这个类中

第二步：ctrl+f找一个叫doDispatch的方法

//入参进来一个request
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {

        HttpServletRequest processedRequest = request;
       处理器执行链
        HandlerExecutionChain mappedHandler = null;
       多部分请求 解析器  （文件上传）
        boolean multipartRequestParsed = false;

        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            try {
           模型（数据）和视图
                ModelAndView err = null;
        异常
                Exception dispatchException = null;

                try {
           //指的是 DispatcherServlet 的实例  看看请求是不是多部分请求 


           <form  enctype="multipart/form-data">  表单有文件域 上传文件了

                    processedRequest = this.checkMultipart(request);

                    multipartRequestParsed = processedRequest != request;
　　　　　　　　　　　　
　　　　　　　　　　　　mappedHandler = this.getHandler(processedRequest);

第三步：ctrl+鼠标左键进入getHandler方法中

  protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {

        handlerMappings单列集合 。Set   List  
        Iterator var2 = this.handlerMappings.iterator();
        HandlerExecutionChain handler;
            if(!var2.hasNext())    return null;
           每next()拿到一个HandlerMapping实例
            HandlerMapping hm = (HandlerMapping)var2.next();
            handler = hm.getHandler(request);
           return handler;
    }

第四步：接着ctrl+鼠标左键找getHandler方法，我们找到的是一个接口，然后ctrl+h找接口的实现类 AbstractHandlerMapping（抽象类）

       public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {

        Object handler = this.getHandlerInternal(request);
        if(handler == null) {
            handler = this.getDefaultHandler();
        }

        if(handler == null) {
            return null;
        } else {
            if(handler instanceof String) {
                String handlerName = (String)handler;  //  /hello
                handler = this.getApplicationContext().getBean(handlerName);
            }

            return this.getHandlerExecutionChain(handler, request);
        }
    }

第五步：找getHandlerExecutionChain方法

   protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = handler instanceof HandlerExecutionChain?(HandlerExecutionChain)handler:new HandlerExecutionChain(handler);
        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        Iterator var5 = this.adaptedInterceptors.iterator();

        while(var5.hasNext()) {
            HandlerInterceptor interceptor = (HandlerInterceptor)var5.next();
            if(interceptor instanceof MappedInterceptor) {
                MappedInterceptor mappedInterceptor = (MappedInterceptor)interceptor;
                if(mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            } else {
                chain.addInterceptor(interceptor);
            }
        }

        return chain;
    }