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);
    }
}