动态代理JDK与cglib的区别之：如何处理被代理方法中的This调用

非常之观常在险远2023-09-11 14:56

关于JDK与cglib动态代理的使用不是本文关注的重点，如有不清楚的同学可以查询相关资料进行了解。本文主要是要讲一下在面对方法存在嵌套调用时JDK与cglib动态代理的区别以及原因。

先看下测试代码，注意下TestProxyJDKImpl的test1方法调用了test2方法即可。

java 复制代码 
        public class Test {


        static interface TestProxyJDK{

                void test1();
                void test2();
            }

       static class TestProxyJDKImp implements TestProxyJDK{

                @Override
                public void test1() {
                    System.out.println("执行test1");
                    test2();
                }

                @Override
                public void test2() {
                    System.out.println("执行test2");
                }
            }



            public static void main(String[] args) throws NoSuchMethodException {
				//输出代理类
                System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

                //创建JDK动态代理对象
                TestProxyJDKImp testProxyJDKImp = new TestProxyJDKImp();
                TestProxyJDK testProxyJDK = (TestProxyJDK) Proxy.newProxyInstance(Test.class.getClassLoader(), TestProxyJDKImp.class.getInterfaces(), new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                        String name = method.getName();
                        System.out.println(name + "方法被拦截前执行方法");
                        method.invoke(testProxyJDKImp, args);
                        System.out.println(name + "方法被拦截后执行方法");
                        return null;
                    }
                });

                //调用test1方法
                testProxyJDK.test1();
				
                //输出代理类
                System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "E:\\cglib");

                
                //创建cglib代理对象
                Enhancer enhancer = new Enhancer();
                enhancer.setSuperclass(TestProxyJDKImp.class);
                enhancer.setCallback(new MethodInterceptor() {
                    @Override
                    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
                        System.out.println("CGLIB拦截前");
                        proxy.invokeSuper(obj,args);
                        System.out.println("CGLIB拦截后");
                        return null;
                    }
                });
                TestProxyJDK testProxyCglib = (TestProxyJDK) enhancer.create();
                
                //调用test1f方法
                testProxyCglib.test1();
            }
        }

为了更好说明情况，我们先把生成的代理类以文件的形式保存下来。对于JDK动态代理，只需要在代码里添加如下一行代码即可。

java 复制代码 
//设置系统属性  1.8还是这种写法
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

生成类如下，主要看下test1和test2方法的代码即可：

java 复制代码 
final class $Proxy0 extends Proxy implements TestProxyJDK {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m4;
    private static Method m0;

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

    public final boolean equals(Object var1) throws  {
        try {
            // 这里的h就是我们创建的InvocationHandler对象
            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);
        }
    }

    public final void test1() throws  {
        try {
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final void test2() throws  {
        try {
            super.h.invoke(this, m4, (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"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("com.xxx.xxx.Test$TestProxyJDK").getMethod("test1");
            m4 = Class.forName("com.xxx.xxx.Test$TestProxyJDK").getMethod("test2");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

如果是cglib那么可以使用下面的方式输出代理类

java 复制代码 
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "your path");

cglib生成的相关类不止一个，这里就贴一下生成的代理类，主要看下test1和test2方法的代码即可：

java 复制代码 
public class Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c extends TestProxyJDKImp implements Factory {
    private boolean CGLIB$BOUND;
    private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
    private static final Callback[] CGLIB$STATIC_CALLBACKS;
    private MethodInterceptor CGLIB$CALLBACK_0;
    private static final Method CGLIB$test2$0$Method;
    private static final MethodProxy CGLIB$test2$0$Proxy;
    private static final Object[] CGLIB$emptyArgs;
    private static final Method CGLIB$test1$1$Method;
    private static final MethodProxy CGLIB$test1$1$Proxy;
    private static final Method CGLIB$finalize$2$Method;
    private static final MethodProxy CGLIB$finalize$2$Proxy;
    private static final Method CGLIB$equals$3$Method;
    private static final MethodProxy CGLIB$equals$3$Proxy;
    private static final Method CGLIB$toString$4$Method;
    private static final MethodProxy CGLIB$toString$4$Proxy;
    private static final Method CGLIB$hashCode$5$Method;
    private static final MethodProxy CGLIB$hashCode$5$Proxy;
    private static final Method CGLIB$clone$6$Method;
    private static final MethodProxy CGLIB$clone$6$Proxy;

    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("com.xxx.xxx.Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c");
        Class var1;
        Method[] var10000 = ReflectUtils.findMethods(new String[]{"finalize", "()V", "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
        CGLIB$finalize$2$Method = var10000[0];
        CGLIB$finalize$2$Proxy = MethodProxy.create(var1, var0, "()V", "finalize", "CGLIB$finalize$2");
        CGLIB$equals$3$Method = var10000[1];
        CGLIB$equals$3$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$3");
        CGLIB$toString$4$Method = var10000[2];
        CGLIB$toString$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$4");
        CGLIB$hashCode$5$Method = var10000[3];
        CGLIB$hashCode$5$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$5");
        CGLIB$clone$6$Method = var10000[4];
        CGLIB$clone$6$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$6");
        var10000 = ReflectUtils.findMethods(new String[]{"test2", "()V", "test1", "()V"}, (var1 = Class.forName("com.xxx.xxx.Test$TestProxyJDKImp")).getDeclaredMethods());
        CGLIB$test2$0$Method = var10000[0];
        CGLIB$test2$0$Proxy = MethodProxy.create(var1, var0, "()V", "test2", "CGLIB$test2$0");
        CGLIB$test1$1$Method = var10000[1];
        CGLIB$test1$1$Proxy = MethodProxy.create(var1, var0, "()V", "test1", "CGLIB$test1$1");
    }

    final void CGLIB$test2$0() {
        super.test2();
    }

    public final void test2() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$test2$0$Method, CGLIB$emptyArgs, CGLIB$test2$0$Proxy);
        } else {
            super.test2();
        }
    }

    final void CGLIB$test1$1() {
        super.test1();
    }

    public final void test1() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$test1$1$Method, CGLIB$emptyArgs, CGLIB$test1$1$Proxy);
        } else {
            super.test1();
        }
    }

    final void CGLIB$finalize$2() throws Throwable {
        super.finalize();
    }

    protected final void finalize() throws Throwable {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$finalize$2$Method, CGLIB$emptyArgs, CGLIB$finalize$2$Proxy);
        } else {
            super.finalize();
        }
    }

    final boolean CGLIB$equals$3(Object var1) {
        return super.equals(var1);
    }

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

        if (var10000 != null) {
            Object var2 = var10000.intercept(this, CGLIB$equals$3$Method, new Object[]{var1}, CGLIB$equals$3$Proxy);
            return var2 == null ? false : (Boolean)var2;
        } else {
            return super.equals(var1);
        }
    }

    final String CGLIB$toString$4() {
        return super.toString();
    }

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

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

    final int CGLIB$hashCode$5() {
        return super.hashCode();
    }

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

        if (var10000 != null) {
            Object var1 = var10000.intercept(this, CGLIB$hashCode$5$Method, CGLIB$emptyArgs, CGLIB$hashCode$5$Proxy);
            return var1 == null ? 0 : ((Number)var1).intValue();
        } else {
            return super.hashCode();
        }
    }

    final Object CGLIB$clone$6() throws CloneNotSupportedException {
        return super.clone();
    }

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

        return var10000 != null ? var10000.intercept(this, CGLIB$clone$6$Method, CGLIB$emptyArgs, CGLIB$clone$6$Proxy) : super.clone();
    }

    public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -1574182249:
            if (var10000.equals("finalize()V")) {
                return CGLIB$finalize$2$Proxy;
            }
            break;
        case -1147892426:
            if (var10000.equals("test1()V")) {
                return CGLIB$test1$1$Proxy;
            }
            break;
        case -1147862635:
            if (var10000.equals("test2()V")) {
                return CGLIB$test2$0$Proxy;
            }
            break;
        case -508378822:
            if (var10000.equals("clone()Ljava/lang/Object;")) {
                return CGLIB$clone$6$Proxy;
            }
            break;
        case 1826985398:
            if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                return CGLIB$equals$3$Proxy;
            }
            break;
        case 1913648695:
            if (var10000.equals("toString()Ljava/lang/String;")) {
                return CGLIB$toString$4$Proxy;
            }
            break;
        case 1984935277:
            if (var10000.equals("hashCode()I")) {
                return CGLIB$hashCode$5$Proxy;
            }
        }

        return null;
    }

    public Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c() {
        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$BIND_CALLBACKS(Object var0) {
        Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c var1 = (Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c)var0;
        if (!var1.CGLIB$BOUND) {
            var1.CGLIB$BOUND = true;
            Object var10000 = CGLIB$THREAD_CALLBACKS.get();
            if (var10000 == null) {
                var10000 = CGLIB$STATIC_CALLBACKS;
                if (var10000 == null) {
                    return;
                }
            }

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

    }

    public Object newInstance(Callback[] var1) {
        CGLIB$SET_THREAD_CALLBACKS(var1);
        Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c var10000 = new Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c var10000 = new Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c var10000 = new Test$TestProxyJDKImp$$EnhancerByCGLIB$$62be832c;
        switch(var1.length) {
        case 0:
            var10000.<init>();
            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();
    }
}

在方法1中调用方法2使用JDK动态代理和使用cglib动态代理有什么区别？

执行上面测试代码的main方法，打印结果如下:

tex 复制代码 
test1方法被拦截前执行方法
执行test1
执行test2
test1方法被拦截后执行方法

CGLIB拦截前
执行test1
CGLIB拦截前
执行test2
CGLIB拦截后
CGLIB拦截后

可以看到，使用JDK代理的时候，在test1方法里调用test2时，test2方法并未被拦截，调用的还是被代理类的test2方法。使用cglib代理的时候，在test1方法里调用test2时，test2也被拦截，调用的是生成的代理类的test2方法。

这是为什么呢？

回到我们生成的代理类，使用JDK代理的时候，调用test1方法，最终执行的是InvocationHandler的invoke方法.

java 复制代码 
super.h.invoke(this, m3, (Object[])null);

在invoke方法里调用被代理的test1方法

java 复制代码 
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                String name = method.getName();
                System.out.println(name + "方法被拦截前执行方法");
                method.invoke(testProxyJDKImp, args);
                System.out.println(name + "方法被拦截后执行方法");
                return null;
            }

注意这里使用 method.invoke(testProxyJDKImp, args)使用的是被代理对象，那么在test1方法里调用this.test2时，这个this自然就是被代理对象，那么test2走的就是原始的方法；

而使用cglib代理的时候，调用test1方法最终执行的是

java 复制代码 
    public final void test1() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            //这个this就是下面的obj，是代理对象
            var10000.intercept(this, CGLIB$test1$1$Method, CGLIB$emptyArgs, CGLIB$test1$1$Proxy);
        } else {
            super.test1();
        }
    }

也就是我们实现的MethodInterceptor的intercept方法里

java 复制代码 
            public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
                System.out.println("CGLIB拦截前");
                proxy.invokeSuper(obj,args);
                System.out.println("CGLIB拦截后");
                return null;
            }

注意，cglib代理时我们从头到尾并不需要被代理类的对象，这里的obj是代理对象，那么自然在调用test1方法时，它里面的this.test2方法里的this就是代理对象，自然执行的是被代理后的test2方法。

说到这里，你有没有想起@Transactional的一种失效的使用场景呢？其实道理都是一样的。

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