代理模式——静态代理、动态代理、cglib代理

谁践踏了优雅 2022-06-13 06:38 325阅读 0赞

# 代理模式——静态代理、动态代理、cglib代理 #

先说一下代理模式，代理模式有很多种，远程代理，虚拟代理，保护代理等等。代理模式总结起来就是包装一个对象并控制对他的访问。比如远程代理就是持有一个远程对象的本地代表。虚拟代理是当创建一个开销较大的对象时，虚拟代理直到我们需要的时候才进行创建，在创建前和创建中时，有虚拟代理来扮演对象的替身。对象创建后，代理就会直接将请求委托给对象。保护代理为一个对象提供了替身或占位符，用户访问这个对象。

本文主要介绍的是保护代理，就是通过为对象提供替身或占位符来访问这个对象。要实现保护代理有很多种方式。常见的有三种，静态代理，动态代理和cglib代理。

下面说一下这三种代理的优劣和使用场景。静态代理需要手工编码，对被代理对象没有特殊要求，如果被代理类的数目有限不多，可以采用静态代理。动态代理采用实现InvocationHandler接口的方式实现代理，被代理对象需要实现特定接口，否则不能使用动态代理。cglib代理使用底层的字节码技术为被代理类创建子类，并在子类中采用方法拦截技术拦截所有父类的方法调用，从而织入逻辑，cglib由于采用的继承的方式，所以不能代理final方法。

远程代理可以参考这篇文章：http://blog.csdn.net/wild46cat/article/details/73824321

虚拟代理可以参考这里：http://www.runoob.com/design-pattern/proxy-pattern.html

好，下面上货。

静态代理：

![Center][]

UserService

package com.xueyou.demo.proxypattern.service;
    
    public interface UserService {
        public void sayHello();
    
        public String getName();
    }

UserServiceImpl

package com.xueyou.demo.proxypattern.serviceImpl;
    
    import com.xueyou.demo.proxypattern.service.UserService;
    
    public class UserServiceImpl implements UserService {
        @Override
        public void sayHello() {
            System.out.println("hello everyone");
        }
    
        @Override
        public String getName() {
            return "xiaoming";
        }
    }

userProxy

package com.xueyou.demo.proxypattern.serviceImpl;
    
    import com.xueyou.demo.proxypattern.service.UserService;
    
    
    public class userProxy implements UserService {
        private UserServiceImpl userServiceimpl;
    
        public userProxy(UserServiceImpl userServiceimpl) {
            this.userServiceimpl = userServiceimpl;
        }
    
        @Override
        public void sayHello() {
            System.out.println("userProxy do something... before");
            userServiceimpl.sayHello();
            System.out.println("userProxy do something... after");
        }
    
        @Override
        public String getName() {
            String result = userServiceimpl.getName();
            return result + " >>>proxy add something here";
        }
    }

App

package com.xueyou.demo.proxypattern;
    
    import com.xueyou.demo.proxypattern.service.UserService;
    import com.xueyou.demo.proxypattern.serviceImpl.UserServiceImpl;
    import com.xueyou.demo.proxypattern.serviceImpl.userProxy;
    
    /**
     * Hello world!
     */
    public class App {
        public static void main(String[] args) {
            UserServiceImpl userServiceImpl = new UserServiceImpl();
            UserService userServiceProxy = new userProxy(userServiceImpl);
            userServiceProxy.sayHello();
            System.out.println(userServiceProxy.getName());
        }
    }

动态代理

![Center 1][]

UserService

package com.xueyou.demo.proxypattern.service;
    
    public interface UserService {
        public void sayHello();
    
        public String returnMessage(String a,int b);
    }

UserServiceImpl

package com.xueyou.demo.proxypattern.serviceImpl;
    
    import com.xueyou.demo.proxypattern.service.UserService;
    
    
    public class UserServiceImpl implements UserService {
        public void sayHello() {
            System.out.println("hello world......");
        }
    
        @Override
        public String returnMessage(String a, int b) {
            return a + b;
        }
    }

MyInvocationHandler

package com.xueyou.demo.proxypattern.proxy;
    
    import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.Method;
    import java.lang.reflect.Proxy;
    
    public class MyInvocationHandler implements InvocationHandler {
        private Object object;
    
        public MyInvocationHandler(Object object) {
            super();
            this.object = object;
        }
    
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            System.out.println("-----before-----");
            Object result = method.invoke(object, args);
            System.out.println("-----after-----");
            return result;
        }
    
        public Object getProxy() {
            return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), this.object.getClass().getInterfaces(), this);
        }
    }

App

package com.xueyou.demo.proxypattern;
    
    import com.xueyou.demo.proxypattern.proxy.MyInvocationHandler;
    import com.xueyou.demo.proxypattern.service.UserService;
    import com.xueyou.demo.proxypattern.serviceImpl.UserServiceImpl;
    
    
    public class App {
        public static void main(String[] args) {
            UserService userService = new UserServiceImpl();
            MyInvocationHandler invocationHandler = new MyInvocationHandler(userService);
            UserService userServiceProxy = (UserService) invocationHandler.getProxy();
    
            userServiceProxy.sayHello();
            String tempResult = userServiceProxy.returnMessage("a", 12);
            System.out.println(tempResult);
        }
    }

cglib代理：

![Center 2][]

UserServiceImpl

package com.xueyou.demo.proxypattern.serviceImpl;
    
    public class UserServiceImpl {
        public void sayHello() {
            System.out.println("hello world");
        }
    
        public String getMessage(String s, int b) {
            return s + b;
        }
    }

UserServiceCglib

package com.xueyou.demo.proxypattern.proxy;
    
    import net.sf.cglib.proxy.Enhancer;
    import net.sf.cglib.proxy.MethodInterceptor;
    import net.sf.cglib.proxy.MethodProxy;
    import java.lang.reflect.Method;
    
    
    public class UserServiceCglib implements MethodInterceptor {
        public Object getInstance(Class clazz) {
            Enhancer enhancer = new Enhancer();
            enhancer.setSuperclass(clazz);
            enhancer.setCallback(this);
            return enhancer.create();
        }
    
        @Override
        public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
            Object result = null;
            System.out.println("-----before-----");
            result = methodProxy.invokeSuper(o, objects);
            System.out.println("-----after-----");
            return result;
        }
    }

App

package com.xueyou.demo.proxypattern;
    
    import com.xueyou.demo.proxypattern.proxy.UserServiceCglib;
    import com.xueyou.demo.proxypattern.serviceImpl.UserServiceImpl;
    
    
    public class App {
        public static void main(String[] args) {
            UserServiceCglib proxy = new UserServiceCglib();
            UserServiceImpl userService = (UserServiceImpl) proxy.getInstance(UserServiceImpl.class);
            userService.sayHello();
            System.out.println(userService.getMessage("aa", 12));
        }
    }

[Center]: /images/20220613/ac092836dde743f2aa56971631942124.png
[Center 1]: /images/20220613/512e0cd08e764e4ca63841338d37b768.png
[Center 2]: /images/20220613/41e432ac110e4d0e95d992a37669db40.png