SpringMVC处理流程介绍

news2024/9/22 7:33:04

SpringMVC请求处理流程

发起请求到前端控制器(DispatcherServlet)
前端控制器请求HandlerMapping查找Handler(可以根据xml配置,注解进行查找)

对应Spring源码

//在类DispatcherServlet里面
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;
            Exception dispatchException = null;

            try {
                processedRequest = this.checkMultipart(request);
                multipartRequestParsed = processedRequest != request;
                mappedHandler = this.getHandler(processedRequest);
                //getHandler方法内部会遍历配置的HandlerMapping实例来找到请求相匹配的Handler
                
            //...其余代码省略
}

处理器映射器HandlerMapping向前端控制器返回Handler,HandlerMapping会把请求映射为HandlerExecutionChain对象(包含一个Handler处理器(页面控制器)对象,多个HandlerInterceptor拦截器对象),通过这种策略模式,很容易添加新的映射策略

对应Spring源码

@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
    if (this.handlerMappings != null) {
        Iterator var2 = this.handlerMappings.iterator();

        while(var2.hasNext()) {
            HandlerMapping mapping = (HandlerMapping)var2.next();
            HandlerExecutionChain handler = mapping.getHandler(request);
            if (handler != null) {
                return handler;
            }
        }
    }

    return null;
}

前端控制器调用处理器去执行Handler

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
   //代码省略......
                mappedHandler = this.getHandler(processedRequest);
                if (mappedHandler == null) {
                    this.noHandlerFound(processedRequest, response);
                    return;
                }

                HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());

    //代码省略

处理器适配器HandlerAdapter将会根据适配去执行Handler
Handler执行完成给适配器返回ModelAndView
处理器适配器向前端控制器返回ModelAndView(ModelAndView是SpringMVC框架的一个底层对象,包括Model和view)

try {
    try {
        ModelAndView mv = null;
        //代码省略....
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
        //代码省略....

前端控制器请求视图解析器去进行视图解析(根据逻辑视图名解析成真正的视图(jsp)),通过这种策略很容易更换其他视图技术,只需要更换视图解析器即可

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
   //代码省略....

            this.processDispatchResult(processedRequest, response, mappedHandler, mv, (Exception)dispatchException);
   //代码省略///