1.1 dynamic proxy -JDK

demo

public interface Person {
    //寻找真爱
    void findLove();
    public String getSex();
    public String getName();
}

@Data
public class XiaoXingXing implements Person {
    private String sex="女";
    private String name="小星星";
    @Override
    public void findLove() {
        System.out.println("我叫"+this.name+",性别:"+this.sex+".我找对象的要求是：");
        System.out.println("高富帅");
        System.out.println("有车有房");
        System.out.println("身高要求180cm,体重70kg");

    }
}

@Data
public class Zhangsan implements Person {
    private String sex ="男";
    private String name = "张三";
    @Override
    public void findLove() {
    }
}

public class Meipo implements InvocationHandler {
    private Person target;
    public Object getInstance(Person target)throws  Exception{
        this.target=target;
        Class clazz = target.getClass();
        System.out.println("被代理对象的class是："+clazz);
        return Proxy.newProxyInstance(clazz.getClassLoader(), clazz.getInterfaces(), this);
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("我是媒婆：你的性别是:"+this.target.getSex()+"得给你找个异性");
        System.out.println("-----------------------------");
        method.invoke(this.target, args);
        System.out.println("-----------------------------");
        return null;
    }
}

public class TestFindLove {
    public static void main(String[] args){
        try {
            Person obj =(Person) new Meipo().getInstance(new XiaoXingXing());
            System.out.println(obj.getClass());
            obj.findLove();
            //代理对象的实现原理
            //1.拿到被代理对象的引用，然后获取它的接口、
            //2.JDK代理 就会重新生成一个类同时实现我们给的代理对象的所实现的接口
            //3.把被代理对象的引用也拿到了
            //4.重新生成一个class字节码
            //5.然后编译
            
            //获取字节码内容，可以看到原理
            byte[] data = ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{Person.class});
            FileOutputStream os = new FileOutputStream("yust5273-proxy\\src\\main\\java\\com\\yust5273\\proxy\\jdk\\$Proxy0.class");
            os.write(data);
            os.close();


//            //简化版
//            Person xiaoxingxing = new XiaoXingXing();
//
//            Person obj = (Person)Proxy.newProxyInstance(xiaoxingxing.getClass().getClassLoader(), xiaoxingxing.getClass().getInterfaces(), (proxy, method, params) -> {
//                System.out.println("反射前");
//                //我是重点1部分   这里是每次调用代理类方法执行的代码！！！              java动态代理本质就是 对原来对象 xiaoxingxing 反射
//                method.invoke(xiaoxingxing, params);
//                System.out.println("反射后");
//                return null;
//            });
//            //这里调用代理类的findLove方法，实际上会执行 “我是重点1部分”的代码
//            obj.findLove();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Verification principle, the compiler will generate a dynamic java class, as follows:

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

import com.yust5273.proxy.jdk.Person;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0 extends Proxy implements Person {
    private static Method m1;
    private static Method m5;
    private static Method m3;
    private static Method m4;
    private static Method m2;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String getSex() throws  {
        try {
            return (String)super.h.invoke(this, m5, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String getName() throws  {
        try {
            return (String)super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final void findLove() throws  {
        try {
            super.h.invoke(this, m4, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m5 = Class.forName("com.yust5273.proxy.jdk.Person").getMethod("getSex");
            m3 = Class.forName("com.yust5273.proxy.jdk.Person").getMethod("getName");
            m4 = Class.forName("com.yust5273.proxy.jdk.Person").getMethod("findLove");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

Reproduced in: https: //www.jianshu.com/p/8be7ae846d2d