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

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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.