java的两种动态代理

一、JDK动态代理

1.1 原理

java动态代理是利用反射机制生成一个实现代理接口的匿名类，在调用具体方法前调用InvokeHandler来处理。

1.2 示例代码

package proxy;

import java.io.Serializable;

public class User implements Serializable {
    private String name;
    private Integer age;

    //省略set、get方法
    //省略toString()方法
}

package proxy;

public interface UserService {
    String addUser(User user);

    Integer deleteUser();
}

package proxy;

public class UserServiceImpl implements UserService {
    @Override
    public String addUser(User user) {
        System.out.println("添加用户");
        return user.toString();
    }

    @Override
    public Integer deleteUser() {
        System.out.println("删除用户");
        return 1;
    }
}

package proxy;

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

public class UserProxyFactory {
    public static UserService createUserService(){
        UserService userService = new UserServiceImpl();

        UserService userServiceProxy = (UserService) Proxy.newProxyInstance(UserService.class.getClassLoader(), userService.getClass().getInterfaces(), new InvocationHandler() {
            /**
             *
             * @param proxy 代理对象
             * @param method 被代理得方法
             * @param args 被代理方法得参数
             * @return
             * @throws Throwable
             */
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                startTrans();
                Object returnObj = method.invoke(userService, args);
                commitTrans();
                return returnObj;
            }
        });
        return userServiceProxy;
    }

    public static void startTrans(){
        System.out.println("开启事务");
    }

    public static void commitTrans(){
        System.out.println("提交事务");
    }
}

package proxy;

public class Test1 {
    public static void main(String[] args) {
        UserService userService = UserProxyFactory.createUserService();
        User user1 = new User();
        user1.setName("zhangsan");
        user1.setAge(11);
        String s = userService.addUser(user1);
        System.out.println("s = " + s);
        userService.deleteUser();
    }
}

==>
开启事务
添加用户
提交事务
s = User{name='zhangsan', age=11}
开启事务
删除用户
提交事务

或者

package proxy;

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

public class UserProxyFactory1 implements InvocationHandler{
    private UserService userService;

    public UserProxyFactory1(UserService userService) {
        this.userService = userService;
    }

    public UserService createUserService(){
        UserService userServiceProxy = (UserService) Proxy.newProxyInstance(UserService.class.getClassLoader(), userService.getClass().getInterfaces(), this);
        return userServiceProxy;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("开启事务");
        Object returnObj = method.invoke(userService, args);
        System.out.println("提交事务");
        return returnObj;
    }


}

package proxy;

public class Test2 {
    public static void main(String[] args) {
        UserProxyFactory1 userProxyFactory1 = new UserProxyFactory1(new UserServiceImpl());
        UserService userService = userProxyFactory1.createUserService();
        User user1 = new User();
        user1.setName("lisi");
        user1.setAge(12);
        String s = userService.addUser(user1);
        System.out.println("s = " + s);
        userService.deleteUser();
    }
}

1.3 优缺点

优点：

• 方法简单
• 无需第三方jar包就可以实现
  缺点：
• 被代理对象必须实现接口

二、cglib动态代理

2.1 原理

利用asm开源包，对代理对象类的class文件加载进来，通过修改其字节码生成子类来处理。

2.2 示例代码

package com.onlymark.proxy;

import com.onlymark.service.UserService;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

/**
 * @auther Onlymark
 * @date 2021/5/7 上午6:05
 */
public class JavaProxyFactory {

	//cglib
	public static UserService createUserServiceProxy(){

		Enhancer enhancer = new Enhancer();
		//设置Enhancer对象的父类
		enhancer.setSuperclass(UserService.class);
		//设置回调方法
		enhancer.setCallback(new MethodInterceptor() {
			/**
			 * obj：cglib生成的代理对象
			 * method：被代理对象方法
			 * args：方法入参
			 * methodProxy: 代理方法
			 */
			@Override
			public Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
				System.out.println("开启事务");
				System.out.println(method.toString());//debug模式下，会多次拦截。因为intercept方法会拦截UserService的所有方法(包括hashcode() toString()等)
				Object object = methodProxy.invokeSuper(obj, args);
				System.out.println("关闭事务");
				return object;
			}
		});
		//创建代理对象
		UserService service = (UserService)enhancer.create();
		//返回代理对象
		return service;
	}

	public static void main(String[] args) {
		UserService userServiceProxy = createUserServiceProxy();
		userServiceProxy.adduser();
		userServiceProxy.deleteuser();
	}
}

或

package com.onlymark.proxy;

import com.onlymark.service.UserService;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

/**
 * @auther Onlymark
 * @date 2021/5/7 上午6:05
 */
public class JavaProxyFactory1 implements MethodInterceptor {
	private UserService userService;

	public JavaProxyFactory1(UserService userService) {
		this.userService = userService;
	}

	//cglib
	public UserService createUserServiceProxy(){

		Enhancer enhancer = new Enhancer();
		//设置Enhancer对象的父类
		enhancer.setSuperclass(UserService.class);
		//设置回调方法
		enhancer.setCallback(this);
		//创建代理对象
		UserService service = (UserService)enhancer.create();
		//返回代理对象
		return service;
	}

	/**
	 * obj：cglib生成的代理对象
	 * method：被代理对象方法
	 * args：方法入参
	 * methodProxy: 代理方法
	 */
	@Override
	public Object intercept(Object obj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
		System.out.println("开启事务");
		Object object = method.invoke(userService, args);
		System.out.println("关闭事务");
		return object;
	}

	public static void main(String[] args) {
		JavaProxyFactory1 javaProxyFactory1 = new JavaProxyFactory1(new UserService());
		UserService userServiceProxy = javaProxyFactory1.createUserServiceProxy();
		userServiceProxy.adduser();

		userServiceProxy.deleteuser();
	}
}

2.3 优缺点

优点：

• CGLIB即使代理类没有实现任何接口也可以实现动态代理功能。
• CGLIB具有简单易用，它的运行速度要远远快于JDK的Proxy动态代理：
  缺点：
• 需要导入相关jar包，现已继承于spring-core.jar