CgLib动态代理学习【Spring AOP基础之一】

　　如果不了解JDK中proxy动态代理机制的可以先查看上篇文章的内容：Java动态代理学习【Spring AOP基础之一】

　　由于Java动态代理Proxy.newProxyInstance()的时候会发现其参数类型是ClassLoader classLoader, Class<?>[] interface, InvocationHandler handler， 只支持根据接口实现代理类，如果所有代码都是自己掌控，当然没有问题。所有的业务逻辑均抽象出接口，然后所有的业务类实现接口，这样所有的业务类均可以使用Java动态代理作为AOP编程的底层支持；但是，假设如果我们想要给一个外部依赖的类添加AOP，并且外部的类并没有实现接口，此时Java动态代理就无能为力了，此时就需要CgLib出场了。

　　业务逻辑类（无接口实现）

public class EasyClass {
    public void easyMethod() {
        System.out.println("这是一个非常简单的方法");
    }
}

　　如果想要使用CgLib给该业务逻辑类创建代理，并且在业务方法的前后等位置增加一些处理逻辑，需要实现net.sf.cglib.proxy.MethodInterceptor接口，并且重写它的intercept方法（代理类中额外的逻辑实现需要在这个函数中实现，是否调用原有类中的方法也需要在这里体现），下面简单在原有方法前后增加一些逻辑；

public class EasyIntercepter 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;
    }
}

　　接下来使用net.sf.cglib.proxy.Enhancer生成相应的代理类即可

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

        EasyClass easyClass =  (EasyClass)Enhancer.create(
                EasyClass.class,
                null, new EasyIntercepter() );
        easyClass.easyMethod();

        //another method
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(EasyClass.class);
        enhancer.setCallback(new EasyIntercepter());
        ((EasyClass)enhancer.create()).easyMethod();
    }
}

　　输出内容如下：

　　从输出内容来看，已经简单的在原有的业务方法前后添加的处理逻辑，所以这个技术就可以用来当做AOP底层生成的技术之一，Spring AOP也正是用这个技术来生成，当配置文件中启用了cglib生成代理类，或者是需要代理的对象没有实现接口，Spring均会使用cglib生成代理类。但是需要使用maven或者gradle引入cglib的引用。

　　其方法应该类似于JDK动态代理。该方法是生成原有类的子类，并使用MethodInterceptor截取每个方法的调用。

　　将上面生成的代理类反向编译如下：

import java.lang.reflect.Method;
import net.sf.cglib.core.ReflectUtils;
import net.sf.cglib.core.Signature;

public class EasyClass$$EnhancerByCGLIB$$48da2939 extends EasyClass 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$easyMethod$0$Method;
    private static final MethodProxy CGLIB$easyMethod$0$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.proxy.EasyClass$$EnhancerByCGLIB$$48da2939");
        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$4");
        CGLIB$easyMethod$0$Method = ReflectUtils.findMethods(new String[]{"easyMethod", "()V"}, (var1 = Class.forName("net.sf.cglib.proxy.EasyClass")).getDeclaredMethods())[0];
        CGLIB$easyMethod$0$Proxy = MethodProxy.create(var1, var0, "()V", "easyMethod", "CGLIB$easyMethod$0");
    }

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

    public final void easyMethod() {
        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$easyMethod$0$Method, CGLIB$emptyArgs, CGLIB$easyMethod$0$Proxy);
        } else {
            super.easyMethod();
        }
    }

    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).booleanValue();
        } 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$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -1577766638:
            if(var10000.equals("easyMethod()V")) {
                return CGLIB$easyMethod$0$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 EasyClass$$EnhancerByCGLIB$$48da2939() {
        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) {
        EasyClass$$EnhancerByCGLIB$$48da2939 var1 = (EasyClass$$EnhancerByCGLIB$$48da2939)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);
        EasyClass$$EnhancerByCGLIB$$48da2939 var10000 = new EasyClass$$EnhancerByCGLIB$$48da2939();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        EasyClass$$EnhancerByCGLIB$$48da2939 var10000 = new EasyClass$$EnhancerByCGLIB$$48da2939();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        EasyClass$$EnhancerByCGLIB$$48da2939 var10000 = new EasyClass$$EnhancerByCGLIB$$48da2939;
        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();
    }
}

　　

　　上述方法中CGLIB$CALLBACK_0就是设置的callback函数，及实现的MethodInceptor接口的逻辑类，所以当调用easyMethod的时候，如果代理类中存在实现MethodInceptor接口的逻辑类，调用其intercept方法，其实这个地方的原理和JDK动态代理有些相似。

　　反编译的方法是git clone cglib的工程文件，找到Enhancer类中创建代理类byte[]的位置，将byte[]数组写成.class文件，然后反编译.class文件。因为和JDK动态代理一样，运行时动态生成类都是动态生成byte[]类结构，然后通过defineClass加载到虚拟机中进一步得到对象。

　　目前不知道如何从一个class类型得到其byte[]文件，所以只能采取上面的方法；关于这个我查阅到两个相关问题，感觉没有很简单的方法，大多回答是基于已有.class文件，但是这里只有动态的class类型，并没有生成.class文件。

　　https://stackoverflow.com/questions/7980133/converting-a-given-class-lets-say-java-lang-object-to-a-byte-array-is-it-po

　　https://stackoverflow.com/questions/2036108/convert-class-object-to-bytes