Struts2非常巧妙地利用递归算法来实现AOP（Aspect Oriented Programming,面向切面编程），我们来简单模仿一下其执行流程。
Action接口：
public interface Action { String execute();}　　MyAction实现Action：
public class MyAction implements Action { @Override public String execute() { System.out.println("=====执行Action====="); return "success"; }}　　Interceptor接口：
public interface Interceptor { String intecept(ActionInvocation invocation);}　　下面分别是Interceptor的三个实现类：
public class TimerInterceptor implements Interceptor{ @Override public String intecept(ActionInvocation invocation) { System.out.println("=====1.执行TimerInterceptor"); String result = invocation.invoke(); System.out.println("=====1.结束执行TimerInterceptor"); return result; }}public class LoggingInterceptor implements Interceptor{ @Override public String intecept(ActionInvocation invocation) { System.out.println("=====2.执行LoggingInterceptor"); String result = invocation.invoke(); System.out.println("=====2.结束执行LoggingInterceptor"); return result; }}public class ChainInterceptor implements Interceptor{ @Override public String intecept(ActionInvocation invocation) { System.out.println("=====3.执行ChainInterceptor"); String result = invocation.invoke(); System.out.println("=====3.结束执行ChainInterceptor"); return result; }}　　下面就是我们的总指挥ActionInvocation接口了：
public interface ActionInvocation { String invoke();}　　ActionInvocation的默认实现类DefaultActionInvocation,所有的调度都是在这里完成的：
public class DefaultActionInvocation implements ActionInvocation{ private int count=0; //定义一个数字来判断interceptors集合是否被执行完 private Action action; private List<Interceptor> interceptors; public DefaultActionInvocation() { interceptors=new ArrayList<Interceptor>(); } @Override public String invoke() { String result=null; if(count<interceptors.size()){ //如果interceptors集合没有执行完，继续执行下一个interceptor /*这步是递归的关键，intercept方法中会调用ActionInvocation的invoke方法，形成递归调用*/ result=interceptors.get(count++).intecept(this); }else if(count==interceptors.size()){ //interceptors集合执行完毕 result=action.execute(); } return result; } //设置Action public void setAction(Action action){ this.action=action; } //添加interceptor public void addInterceptor(Interceptor interceptor){ interceptors.add(interceptor); }}　　好了，该测试一下了，看看效果，测试代码如下：
public class MyTestAOP { public static void main(String[] args) { DefaultActionInvocation actionInvocation=new DefaultActionInvocation(); Interceptor timerInterceptor=new TimerInterceptor(); Interceptor loggingInterceptor=new LoggingInterceptor(); Interceptor chainInteceptor=new ChainInterceptor(); Action action=new MyAction(); //添加拦截器 actionInvocation.addInterceptor(timerInterceptor); actionInvocation.addInterceptor(loggingInterceptor); actionInvocation.addInterceptor(chainInteceptor); //设置Action actionInvocation.setAction(action); //总指挥，发威吧 actionInvocation.invoke(); }}　　犹抱琵琶半遮面的测试结果露面了：
=====1.执行TimerInterceptor=====2.执行LoggingInterceptor=====3.执行ChainInterceptor=====执行Action==========3.结束执行ChainInterceptor=====2.结束执行LoggingInterceptor=====1.结束执行TimerInterceptor　　测试成功，收工，大家一起加油。