设计模式-代理模式(Proxy)

/**
* 抽象主题(房东和中介的共同接口)
*
*/
public interface Person {
 
  void sellHouse();
 
}

/**
* 真实主题(房东)
*
*/
public class HouseOwner implements Person{
   
  @Override
  public void sellHouse() {
    System.out.println("sell House");    
  }
 
}

/**
* 代理对象(中介)
*
*/
public class Agency implements Person{
  private Person houseOwner;//被代理的对象(房东)
 
  Agency(Person houseOwner){
    this.houseOwner = houseOwner;
  }
 
  @Override
  public void sellHouse() {
    System.out.println("中介代理卖房开始");
    houseOwner.sellHouse(); 
    System.out.println("中介代理卖房结束");
  }


}

调用

  //房东自己卖房
  public static void test1(){
    HouseOwner houseOwner = new HouseOwner();
    houseOwner.sellHouse();
  }
 
  //中介代理房东卖房
  public static void test2(){
    HouseOwner houseOwner = new HouseOwner();   
    Person agency = new Agency(houseOwner);
    agency.sellHouse();
  }

代理对象与真实对象功能大量雷同，很繁琐。可以使用JDK提供了Proxy，InvocationHandler来生成代理对象。

public class MyInvocationHandler implements InvocationHandler {
    // 真实主题角色
    private Person target;
    
    public MyInvocationHandler(Person target) {
        this.target = target;
    }

    // 调用Proxy.newProxyInstance(...)时会自动调用这个invoke方法
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("准备");
        Object ret = method.invoke(target, args);// 调用target.xxx(args)
        System.out.println("结束");

        return ret;
    }

}

        //目标对象
        HouseOwner houseOwner = new HouseOwner();
        
        //目标对象的代理对象
        Person agency = (Person) Proxy.newProxyInstance(
                Person.class.getClassLoader(),
                new Class[] { Person.class }, 
                new MyInvocationHandler(houseOwner));
        
        agency.sellHouse();