java动态代理(jdk &cglib)

静态代理
代理类和被代理类 实现同一个接口
缺点就是一个代理类只能针对一个接口

public interface Sale {
	public int saleGoods();
}
public class Factory implements Sale {

	@Override
	public int saleGoods() {
		System.out.println("2块钱，你买不了吃亏");
		return 2;
	}
}
public class Store implements Sale {

	private Factory f;

	public Store(Factory f) {
		this.f = f;
	}

	@Override
	public int saleGoods() {

		int price = f.saleGoods();
		System.out.println("10快钱，你买不了上当");
		return price + 8;
	}
}
public class Test {
	public static void main(String[] args) {
		Factory f = new Factory();
		Store s = new Store(f);
		s.saleGoods();
	}
}

动态代理
动态代理分为两种 jdk and cglib
jdk
jdk 代理主要用到了
接口InvocationHandler 此接口只有一个方法（代码如下）
InvocationHandler的实现类可以理解成具体的代理实现
类Proxy
生成代理的具体的操作类，可以为一个or多个接口动态的实现代理类
缺点 就是被代理的类必须是接口的实现类（依赖于接口）,
如果某些类没有实现接口 则不能用jdk代理

public interface Sale {
	public int saleGoods();
}
public class Factory implements Sale {

	int price;

	@Override
	public int saleGoods() {
		System.out.println("2块钱，买不了吃亏");
		price = 2;
		return price;
	}
}
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class ProxyStore implements InvocationHandler {

	Object factory;

	public Object bind(Object factory) {
		this.factory = factory;
		return Proxy.newProxyInstance(factory.getClass().getClassLoader(),
				factory.getClass().getInterfaces(), this);
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {

		System.out.println("before proxy");
		Object result = method.invoke(factory, args);
		System.out.println("after proxy");
		return result;
	}
}
public class Test {
	public static void main(String[] args) {
		Factory f = new Factory();
		Store s = new Store(f);
		s.saleGoods();
	}
}

cglib
原理是针对target类 生成一个子类 覆盖方法实现增强
缺点 基于继承 无法代理final类(final类无法被继承，如String)
需要的jar包 ：asm-3.3.1，cglib-2.2.jar ps:jar包版本不同可能会报错

public class Factory {

	int price;

	public int saleGoods(int price) {
		System.out.println(price + "块钱，买不了吃亏");
		this.price = price = 2;
		return price;
	}
}
import java.lang.reflect.Method;

import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class ProxyStoreCgLib implements MethodInterceptor {

	Object target;

	public Object getInstanceByMe(Object target) {
		this.target = target;

		Enhancer enhancer = new Enhancer();
		enhancer.setSuperclass(target.getClass());
		enhancer.setCallback(this);

		return enhancer.create();
	}

	@Override
	public Object intercept(Object obj, Method method, Object[] args,
			MethodProxy proxy) throws Throwable {
		System.out.println("before");
		proxy.invokeSuper(obj, args);
		System.out.println("after");
		return null;
	}
}
public class TestPorxy {
	public static void main(String[] args) {
		
		Factory factory = new Factory();
		ProxyStoreCgLib proxyCg = new ProxyStoreCgLib();
		Factory factoryProxy = (Factory) proxyCg.getInstanceByMe(factory);
		factoryProxy.saleGoods(10);
	}
}