java 动态代理 为什么在debug 时会多次执行invoke 内部方法

最近被一个同事问道该问题，有些模糊了，前来验证记录下。

copy了一个网上实例进行验证

package com.huilong.hrs.portal.study.amn.jdkpox;

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

/**
 * @author zhanghuilong
 * @desc
 * @since 2018/12/28
 */
public class Test {
    public static void main(String args[]) {
        ProxyHandler proxy = new ProxyHandler();
        //绑定该类实现的所有接口
        Subject sub = (Subject) proxy.bind(new RealSubject());
        sub.doSomething();
    }
}

interface Subject {
    public void doSomething();
}

class RealSubject implements Subject {
    @Override
    public void doSomething() {
        System.out.println("call doSomething()");
    }
}

class ProxyHandler implements InvocationHandler {
    private Object tar;

    //绑定委托对象，并返回代理类
    public Object bind(Object tar) {
        this.tar = tar;
        //绑定该类实现的所有接口，取得代理类
        return Proxy.newProxyInstance(tar.getClass().getClassLoader(), tar.getClass().getInterfaces(), this);
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable//不依赖具体接口实现
    {
        Object result = null;//被代理的类型为Object基类
        //这里就可以进行所谓的AOP编程了
        //在调用具体函数方法前，执行功能处理
        System.out.println("======调用方法：" + method.getName() + "======");
        System.out.println("proxy = [" + "before" + "]");
        result = method.invoke(tar, args);
        System.out.println("proxy = [" + "after" + "]");
        //在调用具体函数方法后，执行功能处理
        return result;
    }
}

DEBUG 启动单步断点，输出结果如下：可以看出实际执行核心代码只有一处。

Connected to the target VM, address: '127.0.0.1:64388', transport: 'socket'
======调用方法：toString======
proxy = [before]
proxy = [after]
======调用方法：toString======
proxy = [before]
proxy = [after]
======调用方法：doSomething======
======调用方法：toString======
proxy = [before]
proxy = [after]
proxy = [before]
======调用方法：toString======
proxy = [before]
proxy = [after]
call doSomething()
======调用方法：toString======
proxy = [before]
proxy = [after]
proxy = [after]
======调用方法：toString======
proxy = [before]
proxy = [after]
======调用方法：toString======
proxy = [before]
proxy = [after]
======调用方法：toString======
proxy = [before]
proxy = [after]
Disconnected from the target VM, address: '127.0.0.1:64388', transport: 'socket'

再看下正常启动输出结果：

======调用方法：doSomething======
proxy = [before]
call doSomething()
proxy = [after]