JDK动态代理,代理接口没有实现类,实现动态代理方式

public interface Subject2 { 
    String selectById();
}

public class SubjectProxy2<T> implements InvocationHandler { 
    private Class<T> proxyInterface;
    //这里可以维护一个缓存，存这个接口的方法抽象的对象     
    SubjectProxy2(Class<T> proxyInterface){
        this.proxyInterface = proxyInterface;
    } 
 
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        if (method.getName().equals("selectById")){
            //String result = (String) method.invoke(proxyInterface,args);
            //这里可以得到方法抽象对象来调用真的的查询方法
            System.out.println("selectById调用成功");
        }
        return null;
    } 
    public T getProxy(){
        return (T) Proxy.newProxyInstance(proxyInterface.getClassLoader(),new Class[]{proxyInterface},this);
    }
}

public class ProxyTest2 { 
    public static void main(String[] args) {
        SubjectProxy2<Subject2> subjectProxy2 = new SubjectProxy2(Subject2.class);
        Subject2 subject2 = subjectProxy2.getProxy();
        subject2.selectById();
    }
}

//接口
public interface SayService { 
 void say(String name);
}
//实现类
public class SayServiceImpl implements SayService{ 
 @Override
 public void say(String name) {
  System.out.println(name);
 }
}

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method; 
public class WavingInvocationHandler  implements InvocationHandler{ 
 private Object target; 
 public void setTarget(Object target) {
  this.target = target;
 }
 
 @Override
 public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
  System.out.println("方法执行之前！");
  Object obj = method.invoke(target, args);
  System.out.println("方法执行之后！");
  return obj;
 }
}

import sun.misc.ProxyGenerator; 
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.reflect.Proxy;
 
public class Test { 
 public static void main(String[] args) { 
  //接口
  SayService sayService = new SayServiceImpl();
  //织入类
  WavingInvocationHandler handler = new WavingInvocationHandler();
  handler.setTarget(sayService);
  //代理类--增强的对象
  SayService s = (SayService) Proxy.newProxyInstance(
    sayService.getClass().getClassLoader(),
    sayService.getClass().getInterfaces(), handler);
 
  s.say("say()");//执行代理对象完成业务
  
 
  //将jdk中生成代理类输出到本地.Class文件，之后可以通过反编译软件打开查看
  createProxyClassFile("test12345",sayService.getClass().getInterfaces()); 
 }
 
 private static void createProxyClassFile(String name,Class<?> [] interfaces){
  byte[] data = ProxyGenerator.generateProxyClass(name,interfaces);//该方法为jdk中生成代理类的核心方法
  FileOutputStream out =null;
  try {
   out = new FileOutputStream(name+".class");
   System.out.println((new File(name)).getAbsolutePath());
   out.write(data);
  } catch (FileNotFoundException e) {
   e.printStackTrace();
  } catch (IOException e) {
   e.printStackTrace();
  }finally {
   if(null!=out) try {
    out.close();
   } catch (IOException e) {
    e.printStackTrace();
   }
  }
 } 
}

Class<?> cl = getProxyClass0(loader, intfs);

ProxyGenerator.generateProxyClass()

public final class test12345 extends Proxy implements SayService {
    //1、该类实现你传入的接口并实现方法 
    // 2、通过构造方法传入你定义的增强类对象 
    // 3、通过反射该接口，得到接口里的Method对象并传参给增强类，然后执行Invoke实现功能
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;
 
    public test12345(InvocationHandler paramInvocationHandler) {
        super(paramInvocationHandler);//2.此处的super指向Proxy中的构造方法并赋值（下文的h就是此处的增强类对象），
    }
 
    //略去无关的hashcode和equals方法
    public final void say(String paramString) {
        try {
            this.h.invoke(this, m3, new Object[]{paramString});//3.此处的h就是InvocationHandler对象，invoke就是你增强类里的方法，传入接口的方法和参数并执行你增强类里的invoke方法，即完成了整个操作！
        } catch (Error | RuntimeException localError) {
            throw localError;
        } catch (Throwable localThrowable) {
            throw new UndeclaredThrowableException(localThrowable);
        }
    }
 
    static {//1.静态代码块给属性赋值，初始化接口中的方法对象（主要是下面的m3）
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
            m3 = Class.forName("com.chenrui.core.jdk.SayService").getMethod("say", new Class[]{Class.forName("java.lang.String")});
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
        } catch (NoSuchMethodException localNoSuchMethodException) {
            throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
        } catch (ClassNotFoundException localClassNotFoundException) {
            throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
        }
    }
}