jdk动态代理与cglib动态代理

java中的动态代理主要分为两种方式：1.jdk动态代理；2.cglib动态代理
1. jdk动态代理

//首先创建一个接口
public interface Hello {
    String sayhello(String str);
}
//该类实现Hello接口作为被代理的类
public class HelloImpl implements Hello{
    public String sayhello(String str) {
        return "say hello:"+str;
    }
}

//注意，MyInvocationHandler实现InvocationHandler 接口
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;

public class MyInvocationHandler implements InvocationHandler {

    private Hello hello;
    public MyInvocationHandler(Hello hello) {
        this.hello = hello;
    }

//所有的方法执行时都是通过该方法 反射执行
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("+++++before run+++++");
        return method.invoke(hello,args);
    }
}

//执行
MyInvocationHandler myInvocationHandler = new MyInvocationHandler(new HelloImpl());
        Hello hello=(Hello) Proxy.newProxyInstance(Test.class.getClassLoader(),new Class[] {Hello.class},myInvocationHandler);
System.out.println(hello.sayhello("hello world"));

最终生成的代理类如下：

public final class $Proxy0 extends Proxy implements Hello {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    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 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);
        }
    }
//通过反射的方式去执行被代理的方法
    public final String sayhello(String var1) throws  {
        try {
            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 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);
        }
    }
//静态代码块在类初始化时最先执行，通过反射的方式把被代理类所有的方法先创建
    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("com.jw.test.Hello").getMethod("sayhello", Class.forName("java.lang.String"));
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

当代理类被调用的时候，最下面的静态代码块会首先执行，通过反射创建所有的方法，包括hashcode,toString,equals，以及我们在Hello接口中定义的sayHello方法，当通过代理类执行方法调用的时候，都会执行该语句：super.h.invoke()，由于在创建代理类的时候会传入我们实现InvocationHandler接口的类，所以此时的h指的是我们的MyInvocationHandler，所以该语句最后会执行我们写的invoke方法，根据提供的类：hello,提供的方法（最开始静态代码块中定义），以及参数，通过反射的方式执行对应的方法。
所以，jdk动态代理的原理：需要提供接口，代理类会实现该接口从而达到代理原接口实现类的目的。

---

1. cglib动态代理

//首先定义一个类实现MethodInterceptor接口
public class MyMethodInterceptor implements MethodInterceptor {
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("before");
        return proxy.invokeSuper(obj, args);
    }
}

//定义被代理的类
public class HelloConcrete {
    public String sayHello(String str) {
        return "HelloConcrete: " + str;
    }
}
//代理类调用
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(HelloConcrete.class);
enhancer.setCallback(new MyMethodInterceptor());

HelloConcrete hello = (HelloConcrete)enhancer.create();

其生成的代理类如下：

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

package com.jw.test;

import java.lang.reflect.Method;
import net.sf.cglib.core.ReflectUtils;
import net.sf.cglib.core.Signature;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class HelloConcrete$$EnhancerByCGLIB$$ea4a7de9 extends HelloConcrete implements Factory {
    private boolean CGLIB$BOUND;
    public static Object CGLIB$FACTORY_DATA;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private static Object CGLIB$CALLBACK_FILTER;
    private static final Method CGLIB$sayHello$0$Method;
    private static final MethodProxy CGLIB$sayHello$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$equals$1$Method;
    private static final MethodProxy CGLIB$equals$1$Proxy;
    private static final Method CGLIB$toString$2$Method;
    private static final MethodProxy CGLIB$toString$2$Proxy;
    private static final Method CGLIB$hashCode$3$Method;
    private static final MethodProxy CGLIB$hashCode$3$Proxy;
    private static final Method CGLIB$clone$4$Method;
    private static final MethodProxy CGLIB$clone$4$Proxy;

    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("com.jw.test.HelloConcrete$$EnhancerByCGLIB$$ea4a7de9");
        Class var1;
        Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
        CGLIB$equals$1$Method = var10000[0];
        CGLIB$equals$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$1");
        CGLIB$toString$2$Method = var10000[1];
        CGLIB$toString$2$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$2");
        CGLIB$hashCode$3$Method = var10000[2];
        CGLIB$hashCode$3$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$3");
        CGLIB$clone$4$Method = var10000[3];
        CGLIB$clone$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$4");
        CGLIB$sayHello$0$Method = ReflectUtils.findMethods(new String[]{"sayHello", "(Ljava/lang/String;)Ljava/lang/String;"}, (var1 = Class.forName("com.jw.test.HelloConcrete")).getDeclaredMethods())[0];
        CGLIB$sayHello$0$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Ljava/lang/String;", "sayHello", "CGLIB$sayHello$0");
    }

    final String CGLIB$sayHello$0(String var1) {
        return super.sayHello(var1);
    }
//该处定义子类的sayHello方法
    public final String sayHello(String var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$sayHello$0$Method, new Object[]{var1}, CGLIB$sayHello$0$Proxy) : super.sayHello(var1);
    }

    final boolean CGLIB$equals$1(Object var1) {
        return super.equals(var1);
    }

    public final boolean equals(Object var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var2 = var10000.intercept(this, CGLIB$equals$1$Method, new Object[]{var1}, CGLIB$equals$1$Proxy);
            return var2 == null ? false : (Boolean)var2;
        } else {
            return super.equals(var1);
        }
    }

    final String CGLIB$toString$2() {
        return super.toString();
    }

    public final String toString() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy) : super.toString();
    }

    final int CGLIB$hashCode$3() {
        return super.hashCode();
    }

    public final int hashCode() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            Object var1 = var10000.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
            return var1 == null ? 0 : ((Number)var1).intValue();
        } else {
            return super.hashCode();
        }
    }

    final Object CGLIB$clone$4() throws CloneNotSupportedException {
        return super.clone();
    }

    protected final Object clone() throws CloneNotSupportedException {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? var10000.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy) : super.clone();
    }

    public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -1816210712:
            if (var10000.equals("sayHello(Ljava/lang/String;)Ljava/lang/String;")) {
                return CGLIB$sayHello$0$Proxy;
            }
            break;
        case -508378822:
            if (var10000.equals("clone()Ljava/lang/Object;")) {
                return CGLIB$clone$4$Proxy;
            }
            break;
        case 1826985398:
            if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                return CGLIB$equals$1$Proxy;
            }
            break;
        case 1913648695:
            if (var10000.equals("toString()Ljava/lang/String;")) {
                return CGLIB$toString$2$Proxy;
            }
            break;
        case 1984935277:
            if (var10000.equals("hashCode()I")) {
                return CGLIB$hashCode$3$Proxy;
            }
        }

        return null;
    }

    public HelloConcrete$$EnhancerByCGLIB$$ea4a7de9() {
        CGLIB$BIND_CALLBACKS(this);
    }

    public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
        CGLIB$THREAD_CALLBACKS.set(var0);
    }

    public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
        CGLIB$STATIC_CALLBACKS = var0;
    }

    private static final void CGLIB$BIND_CALLBACKS(Object var0) {
        HelloConcrete$$EnhancerByCGLIB$$ea4a7de9 var1 = (HelloConcrete$$EnhancerByCGLIB$$ea4a7de9)var0;
        if (!var1.CGLIB$BOUND) {
            var1.CGLIB$BOUND = true;
            Object var10000 = CGLIB$THREAD_CALLBACKS.get();
            if (var10000 == null) {
                var10000 = CGLIB$STATIC_CALLBACKS;
                if (CGLIB$STATIC_CALLBACKS == null) {
                    return;
                }
            }

            var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
        }

    }

    public Object newInstance(Callback[] var1) {
        CGLIB$SET_THREAD_CALLBACKS(var1);
        HelloConcrete$$EnhancerByCGLIB$$ea4a7de9 var10000 = new HelloConcrete$$EnhancerByCGLIB$$ea4a7de9();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        HelloConcrete$$EnhancerByCGLIB$$ea4a7de9 var10000 = new HelloConcrete$$EnhancerByCGLIB$$ea4a7de9();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        HelloConcrete$$EnhancerByCGLIB$$ea4a7de9 var10000 = new HelloConcrete$$EnhancerByCGLIB$$ea4a7de9;
        switch(var1.length) {
        case 0:
            var10000.();
            CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
            return var10000;
        default:
            throw new IllegalArgumentException("Constructor not found");
        }
    }

    public Callback getCallback(int var1) {
        CGLIB$BIND_CALLBACKS(this);
        MethodInterceptor var10000;
        switch(var1) {
        case 0:
            var10000 = this.CGLIB$CALLBACK_0;
            break;
        default:
            var10000 = null;
        }

        return var10000;
    }

    public void setCallback(int var1, Callback var2) {
        switch(var1) {
        case 0:
            this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
        default:
        }
    }

    public Callback[] getCallbacks() {
        CGLIB$BIND_CALLBACKS(this);
        return new Callback[]{this.CGLIB$CALLBACK_0};
    }

    public void setCallbacks(Callback[] var1) {
        this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
    }

    static {
        CGLIB$STATICHOOK1();
    }
}

该代理类继承需要被代理的方法HelloConcrete，然后覆盖父类的方法，以sayHello方法为例，代理类调用该方法时执行如下代码块：

    public final String sayHello(String var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$sayHello$0$Method, new Object[]{var1}, CGLIB$sayHello$0$Proxy) : super.sayHello(var1);
    }

判断是否存在MethodInterceptor实例（），如果有则执行intercept方法，如果没有则执行父类的原方法。逻辑其实很简单。。。

---

jdk动态代理与cglib的区别：
JDK动态代理只能对实现了接口的类生成代理，而不能针对类 。
CGLIB是针对类实现代理，主要是对指定的类生成一个子类，覆盖其中的方法 。（因为是继承，所以该类或方法最好不要声明成final ，final可以阻止继承和多态）

以上