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