JDK动态代理Demo

JDK动态代理Demo需要几样东西:

• 被代理类
• 被代理类实现的接口
• 代理类
• 测试类

---

被代理类实现的接口

package java_jdk_proxy;

public interface Person {

public void say();
public void eat();
}

被代理类

package java_jdk_proxy;

public class PersonImpl implements Person {

@Override
public void say() {
        System.out.println("person say .. ");
    }

@Override
public void eat() {
        System.out.println("person eat .. ");
    }

}

代理类

package java_jdk_proxy;

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

public class ProxyHandler implements InvocationHandler {

public Object target; // 被代理对象

public ProxyHandler(Object tar) {
this.target = tar;
    }

@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("befor proxy..");
        Object result = method.invoke(target, args);
        System.out.println("after proxy..");
        System.out.println("============");
return result;
    }

}

测试类

package java_jdk_proxy;

import java.lang.reflect.Proxy;

public class ProxyTest {
public static void main(String[] args) {
        PersonImpl personImpl = new PersonImpl();
        ProxyHandler handler = new ProxyHandler(personImpl);
        Person proxy = (Person) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), PersonImpl.class.getInterfaces(), handler);
        proxy.say();
        proxy.eat();
    }

}

运行结果

befor proxy..
person say .. 
after proxy..
============
befor proxy..
person eat .. 
after proxy..
============

总结:JDK动态代理是接口动态代理,被代理类需要实现接口,且只有接口中存在的方法才可以被代理.通过classloader来加载代理类的字节码,使用反射最终执行被代理类的被代理方法.
ps:因为是使用的反射机制执行,所以在性能上不高.