创建代理类：

基类User：

package com.model;

public class User {

}

定义接口UserService：

package com.service;

import com.model.User;

public interface UserService {
    public void save(User user);
    public void update(User user);
}

定义实现类UserServicImpl：

package com.service.impl;

import com.model.User;
import com.service.UserService;

public class UserServiceImpl implements UserService {

    @Override
    public void save(User user) {
        System.out.println("saved!");
    }

    @Override
    public void update(User user) {
        System.out.println("updated!");
    }
    
}

创建代理类ServiceProxy：

package com.proxy;

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

public class ServiceProxy implements InvocationHandler {

    private Object proxyed; 
    public Object createProxyInstance(Object proxyed){   
        this.proxyed=proxyed;   
        return Proxy.newProxyInstance(proxyed.getClass().getClassLoader(), proxyed.getClass().getInterfaces(), this); 
    } 
    @Override 
    public Object invoke(Object proxy, Method method, Object[] args)    throws Throwable {   
        Object result=null;   
        System.out.println("Begin Transaction!");
        result=method.invoke(proxyed, args);
        System.out.println("Stop Transaction!");
        System.out.println("result = " + result);
        return result; 
    } 
    
}

Test测试类：

package com.test;

import com.model.User;
import com.proxy.ServiceProxy;
import com.service.UserService;
import com.service.impl.UserServiceImpl;

public class Test {
    public static void main(String...args) {
        UserService userServiceA = new UserServiceImpl();
        UserService userServiceB = (UserService)new ServiceProxy().createProxyInstance(userServiceA);
        System.out.println(userServiceA.getClass().getPackage() + "." + userServiceA.getClass().getName());
        System.out.println(userServiceB.getClass().getPackage() + "." + userServiceB.getClass().getName());
        userServiceA.save(new User());
    }
}