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/2036108/convert-class-object-to-bytes