JDK动态代理Demo代码，简单易懂

 

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

public class ProxyHandler<T> implements InvocationHandler {

    private T target;

    public ProxyHandler(T target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        System.out.println("before invoke .");
        Object ret = method.invoke(target, args);
        System.out.println("after invoke .");
        return ret;
    }


    public T getProxy() {
        return (T) Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), target.getClass().getInterfaces(), this);
    }
}

　　

 

 

public interface UserService {

    String echo(String content);
}

　　

 

import sun.misc.ProxyGenerator;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

public class UserServiceImpl implements UserService {

    @Override
    public String echo(String content) {
        return content + "_impl";
    }


    public static void main(String[] args) throws IOException {

        UserService us = new UserServiceImpl();
        ProxyHandler<UserService> proxyHandler = new ProxyHandler<>(us);
        UserService userService = proxyHandler.getProxy();


        System.out.println(userService.echo("hello java "));
        System.out.println(userService.getClass());
        generateProxyClassToFile();


    }


    public static void generateProxyClassToFile() throws IOException {
        byte[] bts = ProxyGenerator.generateProxyClass("$Proxy0", new Class[]{UserService.class});
        File file = new File("./", "$Proxy0.class");
        if (!file.exists()) {
            file.createNewFile();
        }
        FileOutputStream fos = new FileOutputStream(file);
        fos.write(bts);
        fos.flush();
        fos.close();
    }
}

　　

代理类的继承接口以及成员变量：

 

 

 

//生成的代理类字节码：

import com.javartisan.springboot.javartisanspringboot.aop.UserService;
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 UserService {
    private static Method m1;
    private static Method m3;
    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 echo(String var1) throws  {
        try { // 代理实现的关键地方，h是继承至Proxy
            return (String)super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    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"));
            m3 = Class.forName("com.javartisan.springboot.javartisanspringboot.aop.UserService").getMethod("echo", Class.forName("java.lang.String"));
            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());
        }
    }
}