代理模式是一种设计模式，简单说即是在不改变源码的情况下，实现对目标对象的功能扩展。

目标：在eat方法执行的前后增加业务逻辑

准备工作

先准备三个基础类

public interface Person { void eat();}/** * 实现了Person接口 */public class OnePerson implements Person{ @Override public void eat() { System.out.println(“我吃饭了”); }}/** * 未实现任何接口 */public class User { public void eat(){ System.out.println(“用户正在吃饭”); }}

静态代理

优点：直观、简单、效率高

缺点：代理对象必须提前写出，如果接口层发生了变化，代理对象的代码也要进行维护

public class PersonProxy implements Person { private Person person; public PersonProxy(Person person) { this.person = person; } @Override public void eat() { System.out.println(“饭前先洗手”); this.person.eat(); System.out.println(“饭后百步走”); }}public class Demo { public static void main(String[] args) { Person person = new PersonProxy(new OnePerson()); person.eat(); }}

动态代理（也叫JDK代理）

缺点：至少包含一个接口

public class JDKDongTaiProxy { public static void main(String[] args) { Person target = new OnePerson(); Person person = (Person) Proxy.newProxyInstance( target.getClass().getClassLoader(), target.getClass().getInterfaces(), new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println(“饭前先洗手”); Object result = method.invoke(target, args); System.out.println(“饭后百步走”); return result; } }); person.eat(); }}

Cglib代理

缺点：依赖cglib包

public class MyMethodInterceptor implements MethodInterceptor { @Override public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable { System.out.println(“饭前先洗手”); Object result = methodProxy.invokeSuper(o, objects); System.out.println(“饭后百步走”); return result; }}public class Demo { public static void main(String[] args) { // 没有实现接口 Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(User.class); enhancer.setCallback(new MyMethodInterceptor()); User user = (User) enhancer.create(); user.eat(); // 实现了接口 enhancer = new Enhancer(); enhancer.setSuperclass(OnePerson.class); enhancer.setCallback(new MyMethodInterceptor()); Person person = (Person) enhancer.create(); person.eat(); }}