Java动态代理

java在java.lang.reflect包中有自己的代理支持，利用这个包可以在运行时动态的创建一个代理类

由于这个类是在运行时动态创建的，因而被称为动态代理

 

使用动态代理实现一个保护代理：

主人可以进入屋子，可以在外部参观屋子，陌生人只可远观，不能进入

 

public interface House {
	public void getIn();
	
	public void visit();
}

public class RealHouse implements House {
	public void getIn() {
		System.out.println("I'm master and I can get in!");
	}

	public void visit() {
		System.out.println("I'm a stranger and I could visit!");
	}
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MasterInvocationHandler implements InvocationHandler {
	private House house;
	
	public MasterInvocationHandler(House house){
		this.house = house;
	}
	
	//As a master,both get in and visit will be fine.
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		if(method.getName().equals("getIn")){
			return method.invoke(house, args);
		}else{
			System.out.println("Can not use this method:"+method.getName());
			return null;
		}
	}
}

public class StrangerInvocationHandler implements InvocationHandler {
	private House house;
	
	public StrangerInvocationHandler(House house){
		this.house = house;
	}
	
	//As a stranger,only visit method was permitted.
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		if(method.getName().equals("visit")){
			return method.invoke(house, args);
		}else{
			System.out.println("Can not use this method:"+method.getName());
			return null;
		}
	}
}

import java.lang.reflect.Proxy;

public class Test {
	public static void main(String[] args) {
		House h = new RealHouse();
		House mh = getHouseProxy(h, "master");
		House sh = getHouseProxy(h, "stranger");
		mh.getIn();
		mh.visit();
		sh.visit();
		sh.getIn();
	}
	
	public static House getHouseProxy(House house,String str){
		if(str.equals("master")){
			return (House)Proxy.newProxyInstance(house.getClass().getClassLoader(), 
					house.getClass().getInterfaces(), 
					new MasterInvocationHandler(house));
		}else{
			return (House)Proxy.newProxyInstance(house.getClass().getClassLoader(), 
					house.getClass().getInterfaces(), 
					new StrangerInvocationHandler(house));
		}
	}
}

运行结果：

I'm master and I can get in!
Can not use this method:visit
I'm a stranger and I could visit!
Can not use this method:getIn

通过上面的例子，可以看到，代码中没有显式创建代理类，代理类是在运行时通过反射由jvm自己创建的