Java代码
- protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
- HttpServletRequest processedRequest = request;
- HandlerExecutionChain mappedHandler = null;
- int interceptorIndex = -1;
- //这里为视图准备好一个ModelAndView，这个ModelAndView持有handler处理请求的结果
- try {
- ModelAndView mv = null;
- boolean errorView = false;
- try {
- processedRequest = checkMultipart(request);
- // Determine handler for the current request.
- // 根据请求得到对应的handler,hander的注册以及getHandler的实现在前面已经分析过
- mappedHandler = getHandler(processedRequest, false);
- if (mappedHandler == null || mappedHandler.getHandler() == null) {
- noHandlerFound(processedRequest, response);
- return;
- }
- // Apply preHandle methods of registered interceptors.
- // 调用hander的拦截器，从HandlerExecutionChain中取出Interceptor进行前处理
- HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
- if (interceptors != null) {
- for (int i = 0; i < interceptors.length; i++) {
- HandlerInterceptor interceptor = interceptors[i];
- if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
- triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
- return;
- }
- interceptorIndex = i;
- }
- }
- // Actually invoke the handler.
- // 这里是实际调用handler的地方，在执行handler之前，用HandlerAdapter先检查一下handler的合法性：是不是按Spring的要求编写的handler
- // handler处理的结果封装到ModelAndView对象，为视图提供展现数据
- HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
- //这里通过调用HandleAdapter的handle方法，实际上触发对Controller的handleRequest方法的调用
- mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
- // Do we need view name translation?
- if (mv != null && !mv.hasView()) {
- mv.setViewName(getDefaultViewName(request));
- }
- // Apply postHandle methods of registered interceptors.
- if (interceptors != null) {
- for (int i = interceptors.length - 1; i >= 0; i--) {
- HandlerInterceptor interceptor = interceptors[i];
- interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
- }
- }
- }
- catch (ModelAndViewDefiningException ex) {
- logger.debug("ModelAndViewDefiningException encountered", ex);
- mv = ex.getModelAndView();
- }
- catch (Exception ex) {
- Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
- mv = processHandlerException(processedRequest, response, handler, ex);
- errorView = (mv != null);
- }
- // Did the handler return a view to render?
- // 这里使用视图对ModelAndView数据的展现
- if (mv != null && !mv.wasCleared()) {
- render(mv, processedRequest, response);
- if (errorView) {
- WebUtils.clearErrorRequestAttributes(request);
- }
- }
- else {
- if (logger.isDebugEnabled()) {
- logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
- "': assuming HandlerAdapter completed request handling");
- }
- }
- // Trigger after-completion for successful outcome.
- triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
- }
- catch (Exception ex) {
- // Trigger after-completion for thrown exception.
- triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
- throw ex;
- }
- catch (Error err) {
- ServletException ex = new NestedServletException("Handler processing failed", err);
- // Trigger after-completion for thrown exception.
- triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, ex);
- throw ex;
- }
- finally {
- // Clean up any resources used by a multipart request.
- if (processedRequest != request) {
- cleanupMultipart(processedRequest);
- }
- }
- }
通过MVC框架，实际上是DispatcherServlet的协调运作，得到了ModelAndView对象作为数据处理结果，最 后，DispatcherServlet把获得的模型数据交给特定的视图对象，从而完成这些数据的视图呈现工作，这个视图呈现由视图对象的render方 法来完成，毫无疑问，对应于不同的视图对象，render方法会完成不同的视图呈现处理，从而为用户提供丰富的Web UI表现。关于这些不同的视图展现，还可以看到很多很有参考意义的开源软件的灵活使用，限于篇幅，这里就不详细说了。
对Spring MVC框架的个人理解
对Spring作为应用平台的Web应用开发而言，Spring为它们提供了Spring MVC框架，作为一个像struts这样的Web框架的替代；当然，作为应用平台，Spring并不会强制应用对Web框架的选择。但对Web应用开发而 言，选择直接使用Spring MVC，可以给应用开发带来许多便利。因为Spring MVC, 毫无疑问，很好的提供了与Web环境中的IoC容器的集成。同时，和其他Web应用一样，使用Spring MVC, 应用只需要专注于处理逻辑和视图呈现的开发（当然这些开发需要符合Spring MVC的开发习惯），在视图呈现部分，Spring MVC同时也集成了许多现有的Web UI实现，比如像Excel, PDF这些文档视图的生成，因为，集成第三方解决方案，实在可以说是Spring的拿手好戏，从这种一致性的开发模式上看，它在很大程度上降低了Web应 用开发的门槛。