回顾一下DispatcherServlet中doDispatch的处理流程

/*** Process the actual dispatching to the handler.* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters* to find the first that supports the handler class.* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers* themselves to decide which methods are acceptable.* @param request current HTTP request* @param response current HTTP response* @throws Exception in case of any kind of processing failure*/protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {HttpServletRequest processedRequest = request;HandlerExecutionChain mappedHandler = null;int interceptorIndex = -1;try {ModelAndView mv;boolean errorView = false;try {// 判断请求是否是多媒体请求processedRequest = checkMultipart(request);// 获取当前请求的处理器HandlerExecutionChainmappedHandler = getHandler(processedRequest, false);if (mappedHandler == null || mappedHandler.getHandler() == null) {//如果没有处理器，则返回一个404noHandlerFound(processedRequest, response);return;}// 获取当前请求的Handler适配器HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.//获取当前请求的请求方法String method = request.getMethod();// 判断当前请求方法是否是GET请求boolean isGet = "GET".equals(method);// 如果是GET请求或者是HEADif (isGet || "HEAD".equals(method)) {//获取最后修改时间long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (logger.isDebugEnabled()) {String requestUri = urlPathHelper.getRequestUri(request);logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);}if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}// 获取拦截器HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();//如果拦截器不为空if (interceptors != null) {for (int i = 0; i < interceptors.length; i++) {HandlerInterceptor interceptor = interceptors[i];//如果处理请求被拦截，则结束请求，否则继续if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);return;}interceptorIndex = i;}}// 调用处理器获取一个视图mv = ha.handle(processedRequest, response, mappedHandler.getHandler());//如果视图不为空，且有view,则设置默认视图名称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);}// 渲染视图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);}}}

可以发现对请求数据的处理是通过HandlerAdapter的handle()方法进行处理。下面将通过AnnotationMethodHandlerAdapter类来说明HandlerAdapter

public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {// 获取处理器的Class对象Class<?> clazz = ClassUtils.getUserClass(handler);Boolean annotatedWithSessionAttributes = this.sessionAnnotatedClassesCache.get(clazz);if (annotatedWithSessionAttributes == null) {// 如果有会话域的参数annotatedWithSessionAttributes = (AnnotationUtils.findAnnotation(clazz, SessionAttributes.class) != null);//将会话域的参数放入到缓存中this.sessionAnnotatedClassesCache.put(clazz, annotatedWithSessionAttributes);}if (annotatedWithSessionAttributes) {// 总是防止缓存的情况下会话属性管理。checkAndPrepare(request, response, this.cacheSecondsForSessionAttributeHandlers, true);//  准备缓存防止会话域参数名称}else {// Uses configured default cacheSeconds setting.checkAndPrepare(request, response, true);}// 如果有必要可以在synchronized同步代码块中执行ivokeHandlerMethod方法，默认是falseif (this.synchronizeOnSession) {// 获取当前请求的sessionHttpSession session = request.getSession(false);if (session != null) {//获取当前session的互斥锁对象Object mutex = WebUtils.getSessionMutex(session);//互斥调用处理器的方法synchronized (mutex) {return invokeHandlerMethod(request, response, handler);}}}return invokeHandlerMethod(request, response, handler);}protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {// 获取指定处理器的ServeltHandlerMethodResovler对象ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);// 获取请求的处理方法Method handlerMethod = methodResolver.resolveHandlerMethod(request);//ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver);//构建一个ServletWebReqeustServletWebRequest webRequest = new ServletWebRequest(request, response);ExtendedModelMap implicitModel = new BindingAwareModelMap();//指定处理Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);// 获取处理后的ModleAndViewModelAndView mav =methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest);methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest);// 返回ModelAndView对象return mav;}

  /*** 对给定的处理器类型创建一个ServeltHandlerMethodResolver*/private ServletHandlerMethodResolver getMethodResolver(Object handler) {// 获取用户定义的类Class handlerClass = ClassUtils.getUserClass(handler);// 从缓存中获取ServletHandlerMethodResolverServletHandlerMethodResolver resolver = this.methodResolverCache.get(handlerClass);//如果缓存中不存在if (resolver == null) {synchronized (this.methodResolverCache) {resolver = this.methodResolverCache.get(handlerClass);if (resolver == null) {// 创建一个ServletHandlerMethodResolver对象并存入缓存resolver = new ServletHandlerMethodResolver(handlerClass);this.methodResolverCache.put(handlerClass, resolver);}}}return resolver;}