springmvc自定义拦截器

  自定义拦截器，我们在开发中基本上都会用到，做一些权限控制，日志等等

    下面用代码来解析下自定义拦截器

    首先定义一个自定义拦截器 

package com.asiainfo.springmvc.intercepter;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import org.apache.log4j.Logger;import org.springframework.web.servlet.HandlerInterceptor;import org.springframework.web.servlet.ModelAndView;import com.asiainfo.springmvc.controller.BaseController;public class DefineIntercepter implements HandlerInterceptor{private static final Logger logger = Logger.getLogger(BaseController.class);public boolean preHandle(HttpServletRequest request,HttpServletResponse response, Object handler) throws Exception {logger.debug("测试拦截器preHandle");return true;}public void postHandle(HttpServletRequest request,HttpServletResponse response, Object handler,ModelAndView modelAndView) throws Exception {logger.debug("测试拦截器postHandle");}public void afterCompletion(HttpServletRequest request,HttpServletResponse response, Object handler, Exception ex)throws Exception {logger.debug("测试拦截器afterCompletion");}}

在spring的xml文件中配置拦截管理器

<!-- 配置拦截器 -->    <mvc:interceptors>       <bean class="com.asiainfo.springmvc.intercepter.DefineIntercepter"></bean>       <!--                  可以定义拦截器拦截某个指定的controller                    比如我现在是配置url路径 是拦截local/*下面的所有请求，如果我变成format/testFormat，那么就不会被拦截            -->       <mvc:interceptor>         <mvc:mapping path="/locale/*"/>         <bean class="com.asiainfo.springmvc.intercepter.SecondIntercepter"></bean>       </mvc:interceptor>       <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"></bean>    </mvc:interceptors>

结果：  

DEBUG [http-bio-8888-exec-8] - 测试拦截器preHandleDEBUG [http-bio-8888-exec-8] - 测试locale===========DEBUG [http-bio-8888-exec-8] - 测试拦截器postHandleDEBUG [http-bio-8888-exec-8] - Rendering view [org.springframework.web.servlet.view.JstlView: name 'success'; URL [/WEB-INF/jsp/success.jsp]] in DispatcherServlet with name 'springmvc'DEBUG [http-bio-8888-exec-8] - Forwarding to resource [/WEB-INF/jsp/success.jsp] in InternalResourceView 'success'DEBUG [http-bio-8888-exec-8] - 测试拦截器afterCompletion

从测试结果中，可以看出，拦截器的执行顺序

   下面我们可以用源码来解读下，拦截器方法是在什么地方执行的

    DispatcherServlet

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {HttpServletRequest processedRequest = request;HandlerExecutionChain mappedHandler = null;boolean multipartRequestParsed = false;WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);try {ModelAndView mv = null;Exception dispatchException = null;try {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// Determine handler for the current request.mappedHandler = getHandler(processedRequest);if (mappedHandler == null || mappedHandler.getHandler() == null) {noHandlerFound(processedRequest, response);return;}// Determine handler adapter for the current request.HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.String method = request.getMethod();boolean isGet = "GET".equals(method);if (isGet || "HEAD".equals(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (logger.isDebugEnabled()) {logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);}if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}if (!mappedHandler.applyPreHandle(processedRequest, response)) { //从这里进入到mappedHandler ,看到拦截器的preHandlereturn;}try {// Actually invoke the handler.mv = ha.handle(processedRequest, response, mappedHandler.getHandler());}finally {if (asyncManager.isConcurrentHandlingStarted()) {return;}}applyDefaultViewName(request, mv);mappedHandler.applyPostHandle(processedRequest, response, mv);//从这里进去看postHandle}}catch (Exception ex) {dispatchException = ex;}    processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);//视图渲染和数据处理}catch (Exception ex) {    triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Error err) {triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);}finally {    if (asyncManager.isConcurrentHandlingStarted())         {// Instead of postHandle and afterCompletionmappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);            return;}// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {if (getInterceptors() != null) {for (int i = 0; i < getInterceptors().length; i++) {HandlerInterceptor interceptor = getInterceptors()[i];if (!interceptor.preHandle(request, response, this.handler)) {triggerAfterCompletion(request, response, null);return false;}this.interceptorIndex = i;}}return true;}

从这个方法可以看出，在执行目标方法之前，就执行了这个前置拦截器方法，如果前置拦截器方法返回false,那么就不会执行目标方法，然后执行AfterCompletion拦截器方法，然后结束。

    然后我们看第二个方法：   

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {if (getInterceptors() == null) {return;}for (int i = getInterceptors().length - 1; i >= 0; i--) {HandlerInterceptor interceptor = getInterceptors()[i];interceptor.postHandle(request, response, this.handler, mv);}}

这个方法是目标方法的后面，但是在视图渲染的前面

  第三个方法：   

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception {boolean errorView = false;if (exception != null) {if (exception instanceof ModelAndViewDefiningException) {logger.debug("ModelAndViewDefiningException encountered", exception);mv = ((ModelAndViewDefiningException) exception).getModelAndView();}else {Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);mv = processHandlerException(request, response, handler, exception);errorView = (mv != null);}}// Did the handler return a view to render?if (mv != null && !mv.wasCleared()) {render(mv, request, response);//这里指渲染视图if (errorView) {WebUtils.clearErrorRequestAttributes(request);}}else {if (logger.isDebugEnabled()) {logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +"': assuming HandlerAdapter completed request handling");}}if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {// Concurrent handling started during a forwardreturn;}if (mappedHandler != null) {mappedHandler.triggerAfterCompletion(request, response, null);//第三个方法}

这样就很简单明了，知道拦截器方法的执行顺序和过程