拦截器(Interceptor)中的invocation.invoke()

 关于在Struts2的自定义的验证拦截器（Interceptor）中的invocation.invoke()是什么意思？

 package com.xjtu.interceptor;  

 import com.opensymphony.xwork2.ActionContext;
 import com.opensymphony.xwork2.ActionInvocation;
 import com.opensymphony.xwork2.interceptor.Interceptor;  

 public class PermissionInterceptor implements Interceptor {  

     /**
      *
      */
     private static final long serialVersionUID = 1L;  

     @Override
     public void destroy() {
         // TODO Auto-generated method stub  

     }  

     @Override
     public void init() {
         // TODO Auto-generated method stub  

     }  

     @Override
     public String intercept(ActionInvocation invocation) throws Exception {
         System.out.println("进入拦截器");
         Object user = ActionContext.getContext().getSession().get("user");
         System.out.println(user);
         if (user != null) {
             return invocation.invoke();
         }
         ActionContext.getContext().put("message", "您无权执行该操作！");
         return "success";
     }  

 }  

 package com.xjtu.soft;  

 public class HelloWorldAction {
     private String message;  

     public String getMessage() {
         return message;
     }  

     public void setMessage(String message) {
         this.message = message;
     }  

     public String execute(){
         System.out.println("执行execute");
         message = "execute";
         return "success";
     }  

     public String addUI() {
         System.out.println("执行addUI");
         message = "addUI";
         return "success";
     }  

 }  

 struts.xml配置自定义的拦截器如下：

 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" "http://struts.apache.org/dtds/struts-2.1.dtd">
 <struts>
     <constant name="struts.action.extension" value="do,action" />
     <constant name="struts.multipart.maxSize" value="10485760" />  

     <package name="itcast" namespace="/test" extends="struts-default">
         <interceptors>
             <interceptor name="permission"
                 class="com.xjtu.interceptor.PermissionInterceptor" />
             <interceptor-stack name="permissionstack">
                 <interceptor-ref name="defaultStack"></interceptor-ref>
                 <interceptor-ref name="permission"></interceptor-ref>
             </interceptor-stack>
         </interceptors>  

         <global-results>
             <result name="success">/WEB-INF/page/message.jsp</result>
         </global-results>  

         <action name="list_*" class="com.xjtu.soft.HelloWorldAction"
             method="{1}">
             <interceptor-ref name="permissionstack"></interceptor-ref>
         </action>
     </package>  

 </struts>      

 invocation.invoke() 就是通知struts2接着干下面的事情
 比如 调用下一个拦截器 或 执行下一个Action
 就等于退出了你自己编写的这个interceptor了

 如何使用struts2拦截器，或者自定义拦截器。特别注意，在使用拦截器的时候，在Action里面必须最后一定要引用struts2自带的拦截器缺省堆栈defaultStack,如下(这里我是引用了struts2自带的checkbox拦截器)：

 <interceptor-ref name="checkbox">
   <param name="uncheckedValue">0</param>
 </interceptor-ref>
 <interceptor-ref name="defaultStack"/>
 ******(必须加，否则出错)