浅谈cglib动态代理

作者: overflow_e4e4 | 来源:发表于2019-05-08 15:58 被阅读0次

cglib的使用与解析

上一篇讲解了java原生的动态代理的使用和部分原理，除了原生的动态代理很多java框架中使用了cglib来做动态代理，so今天准备写一些cglib的使用与解析。

基本使用规则

共需要3个类（比jdk原生少了一个，因为被代理类不需要实现接口）,还是分三步走：

一个代理类

public class Car {

    public void run() {
        System.out.println("car run");
    }
}

一个自定义的MethodInterceptor

public class MyMethodInterceptor implements MethodInterceptor {


    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("before");
        Object result = proxy.invokeSuper(obj,args);
        System.out.println("after");

        return result;
    }
}

最后一个测试main函数

public class Demo {
    public static void main(String[] args) {

        MyMethodInterceptor interceptor = new MyMethodInterceptor();
        Enhancer e = new Enhancer();
        e.setSuperclass(Car.class);
        e.setCallback(interceptor);
        Car car = (Car) e.create();
        car.run();
    }
}

运行结果

before
car run
after

Process finished with exit code 0

一些细节

和jdk原生的代理一样我也想通过阅读源码来找到是否能把cglib生成的class文件存到本地。但是明显cglib的源码逻辑更为复杂，我没有在短时间内找到，所以我查了网上其他人的资料的知道了需要设置cglib生成class文件的目录，就像这样：System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY,"E:\\cglib");,实际上得到源class文件后的我也是一脸懵逼，因为他不止一个。事实上一共生成了5个：

screenshot.png
因为我的测试demo都放在sampes下而且通过类名可以知道 sampes下三个生成的class大概和我的Car被代理类关联比较大。但这也只是猜想，要搞清楚这五个类分别起的什么左右，带着这个问题去看源码可能更好。

现在我分别把上面的五个class文件称为class1,class2,...,class5,
首先我通过断点看到e.create()得到的类是class4

image.png 。
而class4反编译后是这样的：

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

package net.sf.cglib.samples;

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 Car$$EnhancerByCGLIB$$bbb4952c extends Car 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$run$0$Method;
    private static final MethodProxy CGLIB$run$0$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("net.sf.cglib.samples.Car$$EnhancerByCGLIB$$bbb4952c");
        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$4");
        CGLIB$run$0$Method = ReflectUtils.findMethods(new String[]{"run", "()V"}, (var1 = Class.forName("net.sf.cglib.samples.Car")).getDeclaredMethods())[0];
        CGLIB$run$0$Proxy = MethodProxy.create(var1, var0, "()V", "run", "CGLIB$run$0");
    }

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

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

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

    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$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -919875318:
            if (var10000.equals("run()V")) {
                return CGLIB$run$0$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 Car$$EnhancerByCGLIB$$bbb4952c() {
        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) {
        Car$$EnhancerByCGLIB$$bbb4952c var1 = (Car$$EnhancerByCGLIB$$bbb4952c)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);
        Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c;
        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();
    }
}

只看run()方法的话逻辑并不复杂，最终会走到var10000.intercept(this, CGLIB$run$0$Method, CGLIB$emptyArgs, CGLIB$run$0$Proxy);也就是我自己实现的MyMethodInterceptor的intercept方法中。
剩余的一些东西其实通过看了源码也才理解了1/3了更没法通过语言很好的表述，所以就这次先鸽了。希望之后能结合别人和自己的看法再写一篇。

一个坑

最后再讲一下我在写demo调试的时候遇到的一个坑吧
我是这样写的demo：

public class MyMethodInterceptor implements MethodInterceptor {


  public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
      System.out.println("before");
      Object result = proxy.invokeSuper(obj, args);
      System.out.println("method:" + method);
      System.out.println("obj:" + obj);
      System.out.println("after");

      return result;
  }
}

这里主要是 System.out.println("obj:" + obj);这句话有问题，因为这样会调用obj的hashcode方法，而这个obj就是代理类，代理类的hashcode方法会继续调用MyMethodInterceptor.intercept，这样形成了死循环，最终stackoverflow。

浅谈cglib动态代理

cglib的使用与解析

基本使用规则

一些细节

一个坑

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