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();
    }
}