SpringMVC处理流程介绍

SpringMVC请求处理流程

1. 发起请求到前端控制器(DispatcherServlet)
2. 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
}

3. 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;
}

4. 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

5. 处理器适配器HandlerAdapter将会根据适配去执行Handler
6. Handler执行完成给适配器返回ModelAndView
7. 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....

8. 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///

9. 视图解析器向前端控制器返回view
10. 前端控制器进行视图渲染(视图渲染将模型数据(在ModelAndView对象中)填充到request域)
11. 前端控制器向用户响应结果