拦截器是一个类，这个类包含方法，用来解决DRY规则，即代码复用的问题。如果不调用拦截器，代码中需要显示通过代码调用目标方法，定义了拦截器，系统就会自动执行。大部分时候，拦截器方法都是通过代理的方式调用的。

例子：动态代理

Dog.java

  1: package cc.openhome;

  2: public interface Dog {

  3:   //方法的声明

  4:   public void info();

  5:   public void run();

  6: }

  7: 

DogImg.java

  1: package cc.openhome;

  2: public class DogImpl implements Dog {

  3:   //提供方法的实现

  4:   @Override

  5:   public void info() {

  6:     // TODO Auto-generated method stub

  7:     System.out.println("我是一个info猎狗");

  8:   }

  9:   @Override

 10:   public void run() {

 11:     // TODO Auto-generated method stub

 12:     System.out.println("我run奔跑迅速");

 13:   }

 14: }

    DogIntercepter.java系统拦截器

  1: package cc.openhome;

  2: public class DogIntercepter {

  3:   //第一个拦截器方法

  4:   public void method1(){

  5:     System.out.println("=====模拟通用方法1======");

  6:   }

  7:   //第二个拦截器方法

  8:   public void method2(){

  9:     System.out.println("=====模拟通用方法2======");

 10:   }

 11: }

 12: 

    ProxyHandler.java动态调用目标对象的方法

  1: package cc.openhome;

  2: import java.lang.reflect.InvocationHandler;

  3: import java.lang.reflect.Method;

  4: public class ProxyHandler implements InvocationHandler {

  5:   //需被代理的目标

  6:   private Object target;

  7:   //用于设置传入目标对象的方法

  8:   public void setTarget(Object o){

  9:     this.target=o;

 10:   }

 11:   public Object getTarget() {

 12:     return target;

 13:   }

 14:   //创建拦截器实例

 15:   DogIntercepter di = new DogIntercepter();

 16:   //执行代理的目标方法时，该invoke方法会被自动调用

 17:   @Override

 18:   public Object invoke(Object proxy, Method method, Object[] args)

 19:       throws Throwable {

 20:     // TODO Auto-generated method stub

 21:     Object result = null;

 22:     //如果被调用方法的方法名为info

 23:     if(method.getName().equals("info")){

 24:       di.method1();

 25:       result = method.invoke(target, args);

 26:       di.method2();

 27:     }else{

 28:       result = method.invoke(target, args);

 29:     }

 30:     return result;

 31:   }

 32: }

 33: 

    MyProxyFactory.java代理工厂，作用就是根据目标对象生成一个代理对象

  1: package cc.openhome;

  2: import java.lang.reflect.Proxy;

  3: public class MyProxyFactory {

  4:   /*

  5:    * 代理工厂的作用是根据目标对象生成一个代理对象

  6:    * */

  7:   public static Object getProxy(Object object){

  8:     //代理的处理类

  9:     ProxyHandler handler = new ProxyHandler();

 10:     //将该Dog实例托付给代理操作

 11:     handler.setTarget(object);

 12:     return Proxy.newProxyInstance(DogImpl.class.getClassLoader(), object.getClass().getInterfaces(), handler);

 13:   }

 14: }

 15: 

   TestDog.java主程序

  1: package cc.openhome;

  2: public class TestDog {

  3:   public static  void main(String[] args){

  4:     //创建一个Dog实例，该实例将作为被代理的对象

  5:     Dog targetObject = new DogImpl();

  6:     Dog dog=null;

  7:     //以目标对象创建代理

  8:     Object proxy = MyProxyFactory.getProxy(targetObject);

  9:     if(proxy instanceof Dog){

 10:       dog = (Dog)proxy;

 11:     }

 12:     //测试代理的方法

 13:     dog.info();

 14:     dog.run();

 15:   }

 16: }

 17: 

    运行结果

如果想要知道拦截器具体内容知识，参见Struts2拦截器介绍