CGLIB 动态代理用例及源码解析

CGLIB 动态代理

参考链接：https://blog.csdn.net/yhl_jxy/article/details/80633194
参考链接：https://www.jianshu.com/p/001f866a49d7

1.CGLIB 简单介绍

CGLIB简介：CGLIB是一个功能强大，高性能的代码生成包。它为没有实现接口的类提供代理，为JDK的动态代理提供了很好的补充。通常可以使用Java的动态代理创建代理，但当要代理的类没有实现接口或者为了更好的性能，CGLIB是一个好的选择。

CGLIB原理：动态生成一个要代理类的子类，子类重写要代理的类的所有不是final的方法。在子类中采用方法拦截的技术拦截所有父类方法的调用。

2.Demo

2.1 创建需要被代理的类

public class Student2 {public String getName() {System.out.println("我叫红领巾");return "我叫红领巾";}public Integer getAge() {System.out.println("14");return 14;}
}

2.2 生成代理类需实现MethodInterceptor接口

public class MyProxy implements MethodInterceptor {/*** Enhancer.create(superClass,callback)* superClass: 生成代理对象的父类* callback：设置enhancer的回调对象**/public <T> T getProxy(Class<T> clazz){return (T) Enhancer.create(clazz,this);}/*** target：cglib生成的代理对象* method：被代理对象方法* args：方法入参* methodProxy: 代理方法**/@Overridepublic Object intercept(Object target, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {System.out.println("前置");//用MethodProxy 调用父类方法。Object returnObject =  methodProxy.invokeSuper(target,args);System.out.println("后置");return returnObject;}
}

2.3 生成测试类

public class ProxyTest {public static void main(String[] args) {// 代理类class文件存入本地磁盘方便我们反编译查看源码System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "/Users/admin");MyProxy myProxy = new MyProxy();Student2 student2 =  myProxy.getProxy(Student2.class);student2.getName();}
}

2.4 运行结果

2.5 生成的代理类class文件

3. 源码解析

在Demo中通过代理类 Enhancer.create(clazz,this)方法返回被代理类

public static Object create(Class type, Callback callback) {Enhancer e = new Enhancer();e.setSuperclass(type);e.setCallback(callback);return e.create();}

该方法就是创建一个Enhancer类通过create方法返回被代理类

public Object create() {classOnly = false;argumentTypes = null;return createHelper();}

该方法含义就是如果有必要就创建一个新类，并且用指定的回调对象创建一个新的对象实例，

使用的父类的参数的构造方法来实例化父类的部分。核心内容在createHelper()中，源码如下:

private Object createHelper() {this.preValidate();Object key = KEY_FACTORY.newInstance(this.superclass != null ? this.superclass.getName() : null, ReflectUtils.getNames(this.interfaces),this.filter == ALL_ZERO ? null : new WeakCacheKey(this.filter), this.callbackTypes, this.useFactory, this.interceptDuringConstruction,this.serialVersionUID);this.currentKey = key;Object result = super.create(key);return result;}

preValidate()方法校验callbackTypes、filter是否为空，以及为空时的处理。
通过newInstance()方法创建EnhancerKey对象，作为Enhancer父类AbstractClassGenerator.create()方法

protected Object create(Object key) {try {ClassLoader loader = this.getClassLoader();// 如果 data 不存在 ，在多线程环境下添加到CACHEMap<ClassLoader, AbstractClassGenerator.ClassLoaderData> cache = CACHEAbstractClassGenerator.ClassLoaderData data = (AbstractClassGenerator.ClassLoaderData)cache.get(loader);if (data == null) {Class var5 = AbstractClassGenerator.class;synchronized(AbstractClassGenerator.class) {cache = CACHE;data = (AbstractClassGenerator.ClassLoaderData)cache.get(loader);if (data == null) {Map<ClassLoader, AbstractClassGenerator.ClassLoaderData> newCache = new WeakHashMap(cache);data = new AbstractClassGenerator.ClassLoaderData(loader);newCache.put(loader, data);CACHE = newCache;}}}this.key = key;Object obj = data.get(this, this.getUseCache());return obj instanceof Class ? this.firstInstance((Class)obj) : this.nextInstance(obj);} catch (Error | RuntimeException var9) {throw var9;} catch (Exception var10) {throw new CodeGenerationException(var10);}}

真正创建代理对象方法在nextInstance()方法中，该方法为抽象类AbstractClassGenerator的一个方法，签名如下：
abstract protected Object nextInstance(Object instance) throws Exception;

在子类Enhancer中实现，实现源码如下：


protected Object nextInstance(Object instance) {EnhancerFactoryData data = (EnhancerFactoryData) instance;if (classOnly) {return data.generatedClass;}Class[] argumentTypes = this.argumentTypes;Object[] arguments = this.arguments;if (argumentTypes == null) {argumentTypes = Constants.EMPTY_CLASS_ARRAY;arguments = null;}return data.newInstance(argumentTypes, arguments, callbacks);}

通过data.newInstance(argumentTypes, arguments, callbacks)方法，
第一个参数为代理对象的构成器类型，第二个为代理对象构造方法参数，第三个为对应回调对象。
最后根据这些参数，通过反射生成代理对象，源码如下：

/*** Creates proxy instance for given argument types, and assigns the callbacks.* Ideally, for each proxy class, just one set of argument types should be used,* otherwise it would have to spend time on constructor lookup.* Technically, it is a re-implementation of {@link Enhancer#createUsingReflection(Class)},* with "cache {@link #setThreadCallbacks} and {@link #primaryConstructor}"** @see #createUsingReflection(Class)* @param argumentTypes constructor argument types* @param arguments constructor arguments* @param callbacks callbacks to set for the new instance* @return newly created proxy*/public Object newInstance(Class[] argumentTypes, Object[] arguments, Callback[] callbacks) {setThreadCallbacks(callbacks);try {// Explicit reference equality is added here just in case Arrays.equals does not have oneif (primaryConstructorArgTypes == argumentTypes ||Arrays.equals(primaryConstructorArgTypes, argumentTypes)) {// If we have relevant Constructor instance at hand, just call it// This skips "get constructors" machineryreturn ReflectUtils.newInstance(primaryConstructor, arguments);}// Take a slow path if observing unexpected argument typesreturn ReflectUtils.newInstance(generatedClass, argumentTypes, arguments);} finally {// clear thread callbacks to allow them to be gc'dsetThreadCallbacks(null);}}

生成的代理对象的class文件进行反编译之后的代码如下

public class Student2$$EnhancerByCGLIB$$3859af2f extends Student2 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$getName$0$Method;private static final MethodProxy CGLIB$getName$0$Proxy;private static final Object[] CGLIB$emptyArgs;private static final Method CGLIB$getAge$1$Method;private static final MethodProxy CGLIB$getAge$1$Proxy;private static final Method CGLIB$equals$2$Method;private static final MethodProxy CGLIB$equals$2$Proxy;private static final Method CGLIB$toString$3$Method;private static final MethodProxy CGLIB$toString$3$Proxy;private static final Method CGLIB$hashCode$4$Method;private static final MethodProxy CGLIB$hashCode$4$Proxy;private static final Method CGLIB$clone$5$Method;private static final MethodProxy CGLIB$clone$5$Proxy;static void CGLIB$STATICHOOK1() {CGLIB$THREAD_CALLBACKS = new ThreadLocal();CGLIB$emptyArgs = new Object[0];Class clazz1 = Class.forName("com.domain.Student2$$EnhancerByCGLIB$$3859af2f");Class clazz2;CGLIB$equals$2$Method = ReflectUtils.findMethods(new String[] { "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (clazz2 = Class.forName("java.lang.Object")).getDeclaredMethods())[0];CGLIB$equals$2$Proxy = MethodProxy.create(clazz2, clazz1, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2");CGLIB$toString$3$Method = ReflectUtils.findMethods(new String[] { "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (clazz2 = Class.forName("java.lang.Object")).getDeclaredMethods())[1];CGLIB$toString$3$Proxy = MethodProxy.create(clazz2, clazz1, "()Ljava/lang/String;", "toString", "CGLIB$toString$3");CGLIB$hashCode$4$Method = ReflectUtils.findMethods(new String[] { "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (clazz2 = Class.forName("java.lang.Object")).getDeclaredMethods())[2];CGLIB$hashCode$4$Proxy = MethodProxy.create(clazz2, clazz1, "()I", "hashCode", "CGLIB$hashCode$4");CGLIB$clone$5$Method = ReflectUtils.findMethods(new String[] { "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (clazz2 = Class.forName("java.lang.Object")).getDeclaredMethods())[3];CGLIB$clone$5$Proxy = MethodProxy.create(clazz2, clazz1, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5");ReflectUtils.findMethods(new String[] { "equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;" }, (clazz2 = Class.forName("java.lang.Object")).getDeclaredMethods());CGLIB$getName$0$Method = ReflectUtils.findMethods(new String[] { "getName", "()Ljava/lang/String;", "getAge", "()Ljava/lang/Integer;" }, (clazz2 = Class.forName("com.domain.Student2")).getDeclaredMethods())[0];CGLIB$getName$0$Proxy = MethodProxy.create(clazz2, clazz1, "()Ljava/lang/String;", "getName", "CGLIB$getName$0");CGLIB$getAge$1$Method = ReflectUtils.findMethods(new String[] { "getName", "()Ljava/lang/String;", "getAge", "()Ljava/lang/Integer;" }, (clazz2 = Class.forName("com.domain.Student2")).getDeclaredMethods())[1];CGLIB$getAge$1$Proxy = MethodProxy.create(clazz2, clazz1, "()Ljava/lang/Integer;", "getAge", "CGLIB$getAge$1");ReflectUtils.findMethods(new String[] { "getName", "()Ljava/lang/String;", "getAge", "()Ljava/lang/Integer;" }, (clazz2 = Class.forName("com.domain.Student2")).getDeclaredMethods());}final String CGLIB$getName$0() { return super.getName(); }public final String getName() {if (this.CGLIB$CALLBACK_0 == null) {this.CGLIB$CALLBACK_0;CGLIB$BIND_CALLBACKS(this);} return (this.CGLIB$CALLBACK_0 != null) ? (String)this.CGLIB$CALLBACK_0.intercept(this, CGLIB$getName$0$Method, CGLIB$emptyArgs, CGLIB$getName$0$Proxy) : super.getName();}......................................
}

从上述代码可以看到如果被代理类调用getName()方法，就会执行代理类的intercept()方法


//  CGLIB$getName$0$Method = ReflectUtils.findMethods(new String[] { "getName", "()Ljava/lang/String;", "getAge", "()Ljava/lang/Integer;" }, (clazz2 = Class.forName("com.domain.Student2")).getDeclaredMethods())[0];
//  CGLIB$getName$0$Proxy = MethodProxy.create(clazz2, clazz1, "()Ljava/lang/String;", "getName", "CGLIB$getName$0");clazz2 = Class.forName("com.domain.Student2"))
clazz1 =  Class.forName("com.domain.Student2$$EnhancerByCGLIB$$3859af2f");//下面看下MethodProxy.create()方法
c1:  Student
c2: Student$$Enhancer
public static MethodProxy create(Class c1, Class c2, String desc, String name1, String name2) {MethodProxy proxy = new MethodProxy();proxy.sig1 = new Signature(name1, desc);proxy.sig2 = new Signature(name2, desc);proxy.createInfo = new CreateInfo(c1, c2);return proxy;}this.CGLIB$CALLBACK_0.intercept(this, CGLIB$getName$0$Method, CGLIB$emptyArgs, CGLIB$getName$0$Proxy)

在MethodProxy中

对象	实例
c1	Student2
f1	c1的fastClass,更方便调用c1的函数
c2	Student2$$Enhancer，生成的代理对象的实例
f2	c2的fastClass,更加方便调用c2的函数

在intercept()方法中,调用MethodProxy的invokeSuper()方法

 public Object intercept(Object target, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {System.out.println("前置");Object returnObject =  methodProxy.invokeSuper(target,args);System.out.println("后置");return returnObject;}

invokeSuper()

   public Object invokeSuper(Object obj, Object[] args) throws Throwable {try {this.init();MethodProxy.FastClassInfo fci = this.fastClassInfo;//通过下面的代码分析  可知此处调用是 Student$$Enhancer$$FastClss的invoke方法return fci.f2.invoke(fci.i2, obj, args);} catch (InvocationTargetException var4) {throw var4.getTargetException();}}

//下面是init() 方法
private void init() {if (this.fastClassInfo == null) {synchronized(this.initLock) {if (this.fastClassInfo == null) {MethodProxy.CreateInfo ci = this.createInfo;MethodProxy.FastClassInfo fci = new MethodProxy.FastClassInfo();// f1对应的是 Student的FastClassfci.f1 = helper(ci, ci.c1);// f2对应的是 Student$$Enhancer 的FastClassfci.f2 = helper(ci, ci.c2);//i1i2分别是分别在Student$$FastClass和Student$$Enhancer$$FastClss中 调用方法的index.fci.i1 = fci.f1.getIndex(this.sig1);fci.i2 = fci.f2.getIndex(this.sig2);this.fastClassInfo = fci;this.createInfo = null;}}}}//init() 中又调用helper()方法//根据ci得到该方法的委托类，实现类，分别生成这两个类的fastClassprivate static FastClass helper(MethodProxy.CreateInfo ci, Class type) {Generator g = new Generator();g.setType(type);g.setContextClass(type);g.setClassLoader(ci.c2.getClassLoader());g.setNamingPolicy(ci.namingPolicy);g.setStrategy(ci.strategy);g.setAttemptLoad(ci.attemptLoad);return g.create();}

通过反编译得到Student$$EnchancerFastClass的invoke()方法

public Object invoke(int paramInt, Object paramObject, Object[] paramArrayOfObject) throws InvocationTargetException {try {switch (paramInt) {case 0:return new Boolean(((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).equals(paramArrayOfObject[0]));case 1:return ((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).toString();..........//找到Student2$$Enhancer 的getName$0()方法。case 17:return ((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$getName$0();case 18:return ((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$getAge$1();case 19:return new Boolean(((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$equals$2(paramArrayOfObject[0]));case 20:return ((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$toString$3();case 21:return new Integer(((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$hashCode$4());case 22:return ((Student2$$EnhancerByCGLIB$$3859af2f)paramObject).CGLIB$clone$5();} } catch (Throwable throwable) {throw new InvocationTargetException(null);} throw new IllegalArgumentException("Cannot find matching method/constructor");}

在Student$Enhancer中调用CGLIBEnhancer中调用CGLIBEnhancer中调用CGLIBgetName$0()调用 super. name()方法即 Student 的getName方法();

final String CGLIB$getName$0() { return super.getName(); }

思考

思考
1.fastclass比反射快的原因
通过方法前面或者标识符index，利用switch case直接利用对象去调用函数
而反射是java.lang.reflect.Method#invoke,稍微复杂点，这个没研究过具体实现

2.MethodProxy#invoke和MethodProxy#invokeSuper什么区别，即[c1,f1]与[c2,f2]的区别
[c1,f1]对应的是父类的class和fastclass
[c2,f2]对应的是父类的enhanceClass和 enhanceFastClass

3.MethodProxy#init创建fastclass时,每个method在第一次调用时，都会进行
net.sf.cglib.proxy.MethodProxy#init
net.sf.cglib.proxy.MethodProxy#helper
net.sf.cglib.reflect.FastClass.Generator#create
那么为什么对应的fastclass文件只生成了一次(不是一个method调用一次就生成一次)
并且一次就有整个类的信息，而不是只有这个method相关信息呢

第一点：同一个类的fastClass只生成了一次，
net.sf.cglib.reflect.FastClass.Generator#create
net.sf.cglib.core.AbstractClassGenerator#create
里面用了缓存
第二点:一次就有整个类的信息，而不是只有这个method信息
net.sf.cglib.proxy.MethodProxy#create时就传入和class c1,c2
后来创建fastClass时
net.sf.cglib.proxy.MethodProxy#helper
调用了g.setType(type);
在fastClass生成时
net.sf.cglib.reflect.FastClass.Generator#generateClass
用到了这个之前设置好的Class type，也就直到类信息了
invokeSuper的逻辑

4.把invokeSuper改成invoke会怎么样
结论:死循环，堆栈溢出

访问StudentEnhancer中getName(）方法然后进入MethodInterceptor的interceptor()方法又去调用StudentEnhancer中 getName(）方法然后进入MethodInterceptor的interceptor()方法又去调用StudentEnhancer中getName(）方法然后进入MethodInterceptor的interceptor()方法又去调用StudentEnhancer中 getName(）方法 …
导致死循环