//Person.java public class Person { public void sayHello() { System.out.println("Hello!"); } } //Test.java import org.objectweb.asm.ClassWriter; import net.sf.cglib.proxy.Enhancer; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; import java.io.FileOutputStream; import java.lang.reflect.Method; public class Test { public static void main(String[] args) throws Exception { Enhancer enhancer = new Enhancer(); enhancer.setSuperclass(Person.class); //设置生成的类不继承Factory接口 enhancer.setUseFactory(false); enhancer.setCallback(new MethodInterceptor() { public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable { System.out.println("Intercept!"); methodProxy.invokeSuper(o, objects); return null; } }); Person person = (Person) enhancer.create(); person.sayHello(); //以下代码是为了输出cglib生成的类的class文件 ClassWriter cw = new ClassWriter(0); enhancer.generateClass(cw); byte[] klass = cw.toByteArray(); FileOutputStream fileOutputStream = new FileOutputStream(person.getClass().getName()+".class"); fileOutputStream.write(klass); fileOutputStream.close(); } }
使用cglib生成代码的过程很简单：
- new 一个Enhancer对象
- 调用它的setSuperclass()方法设置需要代理的类
- 调用它的setCallback()方法设置拦截被代理类方法时的逻辑
为了简单起见，我们还调用了setUseFactory(false)方法，使得生成的代理类不实现Factory接口（该接口提供了一些生成新对象的和设置对象的Callback的方法）。并且没有使用CallbackFilter。 cglib生成对象时主要的逻辑在Enchancer类的generateClass方法里面：
public void generateClass(ClassVisitor v) throws Exception { Class sc = (superclass == null) ? Object.class : superclass; //如果被代理类是final类型的，抛出异常 if (TypeUtils.isFinal(sc.getModifiers())) throw new IllegalArgumentException("Cannot subclass final class " + sc.getName()); //以下两行代码获得被代理类的非私有构造函数 List constructors = new ArrayList(Arrays.asList(sc.getDeclaredConstructors())); filterConstructors(sc, constructors); // Order is very important: must add superclass, then // its superclass chain, then each interface and // its superinterfaces. List actualMethods = new ArrayList(); List interfaceMethods = new ArrayList(); final Set forcePublic = new HashSet(); //得到被代理类及其父类、接口的非final、非static、非private方法。这些方法是需要代理的（在不考虑CallbackFilter的情况下） getMethods(sc, interfaces, actualMethods, interfaceMethods, forcePublic); //获得需要代理的方法的方法信息 List methods = CollectionUtils.transform(actualMethods, new Transformer() { public Object transform(Object value) { Method method = (Method)value; int modifiers = Constants.ACC_FINAL | (method.getModifiers() & ~Constants.ACC_ABSTRACT & ~Constants.ACC_NATIVE & ~Constants.ACC_SYNCHRONIZED); if (forcePublic.contains(MethodWrapper.create(method))) { modifiers = (modifiers & ~Constants.ACC_PROTECTED) | Constants.ACC_PUBLIC; } return ReflectUtils.getMethodInfo(method, modifiers); } }); ClassEmitter e = new ClassEmitter(v); if (currentData == null) { //生成class文件的版本号、类的访问描述符、类名、父类名、接口，并生成SourceFile属性 e.begin_class(Constants.V1_2, Constants.ACC_PUBLIC, getClassName(), Type.getType(sc), (useFactory ? TypeUtils.add(TypeUtils.getTypes(interfaces), FACTORY) : TypeUtils.getTypes(interfaces)), Constants.SOURCE_FILE); } else { e.begin_class(Constants.V1_2, Constants.ACC_PUBLIC, getClassName(), null, new Type[]{FACTORY}, Constants.SOURCE_FILE); } List constructorInfo = CollectionUtils.transform(constructors, MethodInfoTransformer.getInstance()); //以下生成代理类的字段，可以对照下面的反编译结果观看 //生成private boolean CGLIB$BOUND字段 e.declare_field(Constants.ACC_PRIVATE, BOUND_FIELD, Type.BOOLEAN_TYPE, null); //生成public static Object CGLIB$FACTORY_DATA字段 e.declare_field(Constants.ACC_PUBLIC | Constants.ACC_STATIC, FACTORY_DATA_FIELD, OBJECT_TYPE, null); if (!interceptDuringConstruction) { e.declare_field(Constants.ACC_PRIVATE, CONSTRUCTED_FIELD, Type.BOOLEAN_TYPE, null); } //生成private static final ThreadLocal CGLIB$THREAD_CALLBACKS字段 e.declare_field(Constants.PRIVATE_FINAL_STATIC, THREAD_CALLBACKS_FIELD, THREAD_LOCAL, null); //生成private static final Callback[] CGLIB$STATIC_CALLBACKS字段 e.declare_field(Constants.PRIVATE_FINAL_STATIC, STATIC_CALLBACKS_FIELD, CALLBACK_ARRAY, null); if (serialVersionUID != null) { e.declare_field(Constants.PRIVATE_FINAL_STATIC, Constants.SUID_FIELD_NAME, Type.LONG_TYPE, serialVersionUID); } //以下是生成Callback字段，可以看到，对应每个设置的Callback，都会在代理类中生成一个对应具体类型的字段 for (int i = 0; i < callbackTypes.length; i++) { //在本例中生成的是private MethodInterceptor CGLIB$CALLBACK_0字段，后缀_0代表是在Enhancer中设置的第0个Callback e.declare_field(Constants.ACC_PRIVATE, getCallbackField(i), callbackTypes[i], null); } // This is declared private to avoid "public field" pollution //生成private static Object CGLIB$CALLBACK_FILTER字段。如果Enhancer只设置了一个Callback并且没有设置CallbackFilter，那么会默认对该Enhancer对象添加一个指向第0个Callback的CallbackFilter e.declare_field(Constants.ACC_PRIVATE | Constants.ACC_STATIC, CALLBACK_FILTER_FIELD, OBJECT_TYPE, null); if (currentData == null) { //这个函数生成需要代理类的方法 emitMethods(e, methods, actualMethods); //生成构造函数 emitConstructors(e, constructorInfo); } else { emitDefaultConstructor(e); } //以下三行代码分别生成代理类的CGLIB$SET_THREAD_CALLBACKS、CGLIB$SET_STATIC_CALLBACKS和CGLIB$BIND_CALLBACKS函数 emitSetThreadCallbacks(e); emitSetStaticCallbacks(e); emitBindCallbacks(e); if (useFactory || currentData != null) { int[] keys = getCallbackKeys(); //如果useFactory为true就会生成几个newInstance方法，还有几个操作代理类的Callback的方法 emitNewInstanceCallbacks(e); emitNewInstanceCallback(e); emitNewInstanceMultiarg(e, constructorInfo); emitGetCallback(e, keys); emitSetCallback(e, keys); emitGetCallbacks(e); emitSetCallbacks(e); } e.end_class(); }
使用Bytecode Viewer的CFR反编译生成的代理类如下：
/* * Decompiled with CFR 0_125. * * Could not load the following classes: * Person * Person$$EnhancerByCGLIB$$34b905e4 * net.sf.cglib.core.ReflectUtils * net.sf.cglib.core.Signature * net.sf.cglib.proxy.Callback * net.sf.cglib.proxy.MethodInterceptor * net.sf.cglib.proxy.MethodProxy */ 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.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; /* * Exception performing whole class analysis ignored. */ public class Person$$EnhancerByCGLIB$$34b905e4 extends Person { 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$sayHello$0$Method; private static final MethodProxy CGLIB$sayHello$0$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$STATICHOOK2() { CGLIB$THREAD_CALLBACKS = new ThreadLocal(); CGLIB$emptyArgs = new Object[0]; Class class_ = Class.forName("Person$$EnhancerByCGLIB$$34b905e4"); Class class_2 = Class.forName("java.lang.Object"); Method[] arrmethod = ReflectUtils.findMethods((String[])new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (Method[])class_2.getDeclaredMethods()); CGLIB$equals$1$Method = arrmethod[0]; CGLIB$equals$1$Proxy = MethodProxy.create(class_2, class_, (String)"(Ljava/lang/Object;)Z", (String)"equals", (String)"CGLIB$equals$1"); CGLIB$toString$2$Method = arrmethod[1]; CGLIB$toString$2$Proxy = MethodProxy.create(class_2, class_, (String)"()Ljava/lang/String;", (String)"toString", (String)"CGLIB$toString$2"); CGLIB$hashCode$3$Method = arrmethod[2]; CGLIB$hashCode$3$Proxy = MethodProxy.create(class_2, class_, (String)"()I", (String)"hashCode", (String)"CGLIB$hashCode$3"); CGLIB$clone$4$Method = arrmethod[3]; CGLIB$clone$4$Proxy = MethodProxy.create(class_2, class_, (String)"()Ljava/lang/Object;", (String)"clone", (String)"CGLIB$clone$4"); class_2 = Class.forName("Person"); CGLIB$sayHello$0$Method = ReflectUtils.findMethods((String[])new String[]{"sayHello", "()V"}, (Method[])class_2.getDeclaredMethods())[0]; CGLIB$sayHello$0$Proxy = MethodProxy.create(class_2, class_, (String)"()V", (String)"sayHello", (String)"CGLIB$sayHello$0"); } final void CGLIB$sayHello$0() { super.sayHello(); } public final void sayHello() { MethodInterceptor methodInterceptor = this.CGLIB$CALLBACK_0; if (methodInterceptor == null) { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)this); methodInterceptor = this.CGLIB$CALLBACK_0; } if (methodInterceptor != null) { Object object = methodInterceptor.intercept((Object)this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy); return; } super.sayHello(); } final boolean CGLIB$equals$1(Object object) { return super.equals(object); } public final boolean equals(Object object) { MethodInterceptor methodInterceptor = this.CGLIB$CALLBACK_0; if (methodInterceptor == null) { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)this); methodInterceptor = this.CGLIB$CALLBACK_0; } if (methodInterceptor == null) return super.equals(object); Object object2 = methodInterceptor.intercept((Object)this, CGLIB$equals$1$Method, new Object[]{object}, CGLIB$equals$1$Proxy); if (object2 == null) { return false; } boolean bl = (Boolean)object2; return bl; } final String CGLIB$toString$2() { return super.toString(); } public final String toString() { MethodInterceptor methodInterceptor = this.CGLIB$CALLBACK_0; if (methodInterceptor == null) { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)this); methodInterceptor = this.CGLIB$CALLBACK_0; } if (methodInterceptor == null) return super.toString(); return (String)methodInterceptor.intercept((Object)this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy); } final int CGLIB$hashCode$3() { return super.hashCode(); } public final int hashCode() { MethodInterceptor methodInterceptor = this.CGLIB$CALLBACK_0; if (methodInterceptor == null) { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)this); methodInterceptor = this.CGLIB$CALLBACK_0; } if (methodInterceptor == null) return super.hashCode(); Object object = methodInterceptor.intercept((Object)this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy); if (object == null) { return 0; } int n = ((Number)object).intValue(); return n; } final Object CGLIB$clone$4() throws CloneNotSupportedException { return super.clone(); } protected final Object clone() throws CloneNotSupportedException { MethodInterceptor methodInterceptor = this.CGLIB$CALLBACK_0; if (methodInterceptor == null) { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)this); methodInterceptor = this.CGLIB$CALLBACK_0; } if (methodInterceptor == null) return super.clone(); return methodInterceptor.intercept((Object)this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy); } public static MethodProxy CGLIB$findMethodProxy(Signature signature) { String string = signature.toString(); switch (string.hashCode()) { case -508378822: { if (!string.equals("clone()Ljava/lang/Object;")) return null; return CGLIB$clone$4$Proxy; } case 1535311470: { if (!string.equals("sayHello()V")) return null; return CGLIB$sayHello$0$Proxy; } case 1826985398: { if (!string.equals("equals(Ljava/lang/Object;)Z")) return null; return CGLIB$equals$1$Proxy; } case 1913648695: { if (!string.equals("toString()Ljava/lang/String;")) return null; return CGLIB$toString$2$Proxy; } case 1984935277: { if (!string.equals("hashCode()I")) return null; return CGLIB$hashCode$3$Proxy; } } return null; } public Person$$EnhancerByCGLIB$$34b905e4() { Person$$EnhancerByCGLIB$$34b905e4 person$$EnhancerByCGLIB$$34b905e4 = this; Person$$EnhancerByCGLIB$$34b905e4.CGLIB$BIND_CALLBACKS((Object)person$$EnhancerByCGLIB$$34b905e4); } public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] arrcallback) { CGLIB$THREAD_CALLBACKS.set(arrcallback); } public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] arrcallback) { CGLIB$STATIC_CALLBACKS = arrcallback; } private static final void CGLIB$BIND_CALLBACKS(Object object) { Person$$EnhancerByCGLIB$$34b905e4 person$$EnhancerByCGLIB$$34b905e4 = (Person$$EnhancerByCGLIB$$34b905e4)object; if (person$$EnhancerByCGLIB$$34b905e4.CGLIB$BOUND) return; person$$EnhancerByCGLIB$$34b905e4.CGLIB$BOUND = true; Object t = CGLIB$THREAD_CALLBACKS.get(); if (t == null && (v783 = CGLIB$STATIC_CALLBACKS) == null) { return; } person$$EnhancerByCGLIB$$34b905e4.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])t)[0]; } static { Person$$EnhancerByCGLIB$$34b905e4.CGLIB$STATICHOOK2(); } }
可以看到，在创建一个代理类的对象的时候，会先加载这个类，也就调用了类的静态方法CGLIB$STATICHOOK2()，在这个函数中对类的其它静态字段进行了初始化，比如对应每个需要代理的方法都生成两个字段，一个是用于反射的Method对象，另一个是用于加快方法调用、避免反射带来的开销的MethodProxy对象。然后在构造函数里面调用了CGLIB$BIND_CALLBACKS(this)，在CGLIB$BIND_CALLBACKS方法中会把private MethodInterceptor CGLIB$CALLBACK_0字段和设置的静态变量ThreadLocal CGLIB$THREAD_CALLBACKS进行绑定，也就是说，设置的Callback并不是硬编码在生成的代理类里面的，而是可以动态地设置。
由于代理类继承了被代理类，所以调用sayHello()方法时会直接调用代理类的sayHello()方法，而在代理类的方法中，调用了Callback的逻辑。
