jdk动态代理是如何实现的(使用JDK动态代理实现日志的打印)

package com.spring.aop.beans;

public interface Calculator {
    int add(int a,int b);
    int sub(int a,int b);
    int mul(int a,int b);
    int div(int a,int b);
}

package com.spring.aop.beans;

import org.springframework.stereotype.Repository;

@Repository(value = "calculator")
public class CalculatorImpl implements Calculator {
    @Override
    public int add(int a, int b) {
        int result = a + b;
        return result;
    }

    @Override
    public int sub(int a, int b) {
        int result = a - b;
        return result;
    }

    @Override
    public int mul(int a, int b) {
        int result = a * b;
        return result;
    }

    @Override
    public int div(int a, int b) {
        int result = a / b;
        return result;
    }
}

package com.spring.log;

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

public class LoggingProxy {
    //被代理的对象
    private  Object target;

    public LoggingProxy(Object target) {
        this.target = target;
    }

    public Object getProxy() {
        //获取被代理对象的类加载器
        ClassLoader classLoader =target.getClass().getClassLoader();
        //获取被代理对象实现的接口
        Class[] interfaces = target.getClass().getInterfaces();
       Object proxy= Proxy.newProxyInstance(classLoader, interfaces, new InvocationHandler() {
            
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //获取方法名
                String methodName =method.getName();
                System.out.println("Logging: The method "+methodName+"begins with"+ Arrays.toString(args));
                //执行方法，即方法的调用转到被代理对象上
                Object result=method.invoke(target,args);
                System.out.println("Logging: The method "+methodName+"returns"+ result);
                return result;
            }
        });
        return proxy;
    }
}

@Test
public void testProxy(){
    Calculator cal = new CalculatorImpl();
    //获取代理对象
    Calculator calculator = (Calculator) new LoggingProxy(cal).getProxy();
    //调用加减乘除的方法
    calculator.add(10,2);
    calculator.sub(10,2);
    calculator.mul(10,2);
    calculator.div(10,2);
}