【Java】JDK动态代理

一. JDK动态代理示例

1. 接口

public interface UserService {
    void addUser(String name);
    String getUser(String name);
}

---

2. 被代理对象

public class UserServiceImpl implements UserService {

    public void addUser(String name) {
        System.out.println("add user into database.");
    }
    
    public String getUser(String name) {
        
        System.out.println("getUser from database.");
        return name;
    }
}

---

3. 代理工具类

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

public class ProxyUtil implements InvocationHandler {

    private Object target ;//需要代理的目标对象
    
    //定义获取代理对象方法
    public Object getProxy(Object targetObject){
    
        this.target = targetObject;
        
        //JDK动态代理只能针对实现了接口的类进行代理
        return Proxy.newProxyInstance(targetObject.getClass().getClassLoader(), targetObject.getClass().getInterfaces(), this);
    }
    
    
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    
        System.out.println("JDK动态代理前置逻辑");
        
        Object result = method.invoke(target, args);
        
        System.out.println("JDK动态代理后续逻辑");
        return result;
    }
}

---

4. 使用代理类

import java.lang.reflect.Proxy;

public class ProxyTest {

    public static void main(String[] args){
    
        // 被代理的对象
        UserServiceImpl userServiceImpl = new UserServiceImpl();    
        
        // 生成代理对象
        UserService userService = (UserService)new ProxyUtil().getProxy(userServiceImpl);
        
        userService.getUser("1");
        userService.addUser("1");
    }
}

---

5. 执行结果

JDK动态代理前置逻辑
getUser from database.
JDK动态代理后续逻辑

JDK动态代理前置逻辑
add user into database.
JDK动态代理后续逻辑

---

二. JDK动态代理说明

1. 获取代理对象：ProxyUtil.getProxy

2. 调用代理方法：ProxyUtil.invoke