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前言
Github:https://github.com/yihonglei/thinking-in-spring(spring工程)
一 CGLIB介绍
CGLIB(Code Generation Library)是一个开源项目!是一个强大的,高性能,高质量的Code生成类库,
它可以在运行期扩展Java类与实现Java接口。Hibernate用它来实现PO(Persistent Object 持久化对象)字节码的动态生成。
CGLIB是一个强大的高性能的代码生成包。它广泛的被许多AOP的框架使用,例如Spring AOP为他们提供
方法的interception(拦截)。CGLIB包的底层是通过使用一个小而快的字节码处理框架ASM,来转换字节码并生成新的类。
除了CGLIB包,脚本语言例如Groovy和BeanShell,也是使用ASM来生成java的字节码。当然不鼓励直接使用ASM,
因为它要求你必须对JVM内部结构包括class文件的格式和指令集都很熟悉。
二 CGLIB动态代理实例
实现一个业务类,注意,这个业务类并没有实现任何接口:
package com.jpeony.spring.proxy.cglib;
public class HelloService {
public HelloService() {
System.out.println("HelloService构造");
}
/**
* 该方法不能被子类覆盖,Cglib是无法代理final修饰的方法的
*/
final public String sayOthers(String name) {
System.out.println("HelloService:sayOthers>>"+name);
return null;
}
public void sayHello() {
System.out.println("HelloService:sayHello");
}
}
自定义MethodInterceptor:
package com.jpeony.spring.proxy.cglib;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
/**
* 自定义MethodInterceptor
*/
public class MyMethodInterceptor implements MethodInterceptor{
/**
* sub:cglib生成的代理对象
* method:被代理对象方法
* objects:方法入参
* methodProxy: 代理方法
*/
@Override
public Object intercept(Object sub, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
System.out.println("======插入前置通知======");
Object object = methodProxy.invokeSuper(sub, objects);
System.out.println("======插入后者通知======");
return object;
}
}
生成CGLIB代理对象调用目标方法:
package com.jpeony.spring.proxy.cglib;
import net.sf.cglib.core.DebuggingClassWriter;
import net.sf.cglib.proxy.Enhancer;
public class Client {
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, "D:\\code");
// 通过CGLIB动态代理获取代理对象的过程
Enhancer enhancer = new Enhancer();
// 设置enhancer对象的父类
enhancer.setSuperclass(HelloService.class);
// 设置enhancer的回调对象
enhancer.setCallback(new MyMethodInterceptor());
// 创建代理对象
HelloService proxy= (HelloService)enhancer.create();
// 通过代理对象调用目标方法
proxy.sayHello();
}
}
运行结果:
三 CGLIB动态代理源码分析
实现CGLIB动态代理必须实现MethodInterceptor(方法拦截器)接口,源码如下:
/*
* Copyright 2002,2003 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package net.sf.cglib.proxy;
/**
* General-purpose {@link Enhancer} callback which provides for "around advice".
* @author Juozas Baliuka <a href="mailto:baliuka@mwm.lt">baliuka@mwm.lt</a>
* @version $Id: MethodInterceptor.java,v 1.8 2004/06/24 21:15:20 herbyderby Exp $
*/
public interface MethodInterceptor
extends Callback
{
/**
* All generated proxied methods call this method instead of the original method.
* The original method may either be invoked by normal reflection using the Method object,
* or by using the MethodProxy (faster).
* @param obj "this", the enhanced object
* @param method intercepted Method
* @param args argument array; primitive types are wrapped
* @param proxy used to invoke super (non-intercepted method); may be called
* as many times as needed
* @throws Throwable any exception may be thrown; if so, super method will not be invoked
* @return any value compatible with the signature of the proxied method. Method returning void will ignore this value.
* @see MethodProxy
*/
public Object intercept(Object obj, java.lang.reflect.Method method, Object[] args,
MethodProxy proxy) throws Throwable;
}
这个接口只有一个intercept()方法,这个方法有4个参数:
1)obj表示增强的对象,即实现这个接口类的一个对象;
2)method表示要被拦截的方法;
3)args表示要被拦截方法的参数;
4)proxy表示要触发父类的方法对象;
在上面的Client代码中,通过Enhancer.create()方法创建代理对象,create()方法的源码:
/**
* Generate a new class if necessary and uses the specified
* callbacks (if any) to create a new object instance.
* Uses the no-arg constructor of the superclass.
* @return a new instance
*/
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() {
preValidate();
Object key = KEY_FACTORY.newInstance((superclass != null) ? superclass.getName() : null,
ReflectUtils.getNames(interfaces),
filter == ALL_ZERO ? null : new WeakCacheKey<CallbackFilter>(filter),
callbackTypes,
useFactory,
interceptDuringConstruction,
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
创建代理对象的参数。
protected Object create(Object key) {
try {
ClassLoader loader = getClassLoader();
Map<ClassLoader, ClassLoaderData> cache = CACHE;
ClassLoaderData data = cache.get(loader);
if (data == null) {
synchronized (AbstractClassGenerator.class) {
cache = CACHE;
data = cache.get(loader);
if (data == null) {
Map<ClassLoader, ClassLoaderData> newCache = new WeakHashMap<ClassLoader, ClassLoaderData>(cache);
data = new ClassLoaderData(loader);
newCache.put(loader, data);
CACHE = newCache;
}
}
}
this.key = key;
Object obj = data.get(this, getUseCache());
if (obj instanceof Class) {
return firstInstance((Class) obj);
}
return nextInstance(obj);
} catch (RuntimeException e) {
throw e;
} catch (Error e) {
throw e;
} catch (Exception e) {
throw new CodeGenerationException(e);
}
}
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);
}
看看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 one
if (primaryConstructorArgTypes == argumentTypes ||
Arrays.equals(primaryConstructorArgTypes, argumentTypes)) {
// If we have relevant Constructor instance at hand, just call it
// This skips "get constructors" machinery
return ReflectUtils.newInstance(primaryConstructor, arguments);
}
// Take a slow path if observing unexpected argument types
return ReflectUtils.newInstance(generatedClass, argumentTypes, arguments);
} finally {
// clear thread callbacks to allow them to be gc'd
setThreadCallbacks(null);
}
}
最后生成代理对象:
将其反编译后代码如下:
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package com.jpeony.spring.proxy.cglib;
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.Factory;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
public class HelloService$$EnhancerByCGLIB$$be45efdd extends HelloService 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$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$STATICHOOK1() {
CGLIB$THREAD_CALLBACKS = new ThreadLocal();
CGLIB$emptyArgs = new Object[0];
Class var0 = Class.forName("com.jpeony.spring.proxy.cglib.HelloService$$EnhancerByCGLIB$$be45efdd");
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$4");
CGLIB$sayHello$0$Method = ReflectUtils.findMethods(new String[]{"sayHello", "()V"}, (var1 = Class.forName("com.jpeony.spring.proxy.cglib.HelloService")).getDeclaredMethods())[0];
CGLIB$sayHello$0$Proxy = MethodProxy.create(var1, var0, "()V", "sayHello", "CGLIB$sayHello$0");
}
final void CGLIB$sayHello$0() {
super.sayHello();
}
public final void sayHello() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
var10000.intercept(this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy);
} else {
super.sayHello();
}
}
final boolean CGLIB$equals$1(Object var1) {
return super.equals(var1);
}
public final boolean equals(Object var1) {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == 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;
} else {
return super.equals(var1);
}
}
final String CGLIB$toString$2() {
return super.toString();
}
public final String toString() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (var10000 == 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 (var10000 == 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 (var10000 == 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$findMethodProxy(Signature var0) {
String var10000 = var0.toString();
switch(var10000.hashCode()) {
case -508378822:
if (var10000.equals("clone()Ljava/lang/Object;")) {
return CGLIB$clone$4$Proxy;
}
break;
case 1535311470:
if (var10000.equals("sayHello()V")) {
return CGLIB$sayHello$0$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 HelloService$$EnhancerByCGLIB$$be45efdd() {
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) {
HelloService$$EnhancerByCGLIB$$be45efdd var1 = (HelloService$$EnhancerByCGLIB$$be45efdd)var0;
if (!var1.CGLIB$BOUND) {
var1.CGLIB$BOUND = true;
Object var10000 = CGLIB$THREAD_CALLBACKS.get();
if (var10000 == null) {
var10000 = CGLIB$STATIC_CALLBACKS;
if (var10000 == null) {
return;
}
}
var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
}
}
public Object newInstance(Callback[] var1) {
CGLIB$SET_THREAD_CALLBACKS(var1);
HelloService$$EnhancerByCGLIB$$be45efdd var10000 = new HelloService$$EnhancerByCGLIB$$be45efdd();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Callback var1) {
CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
HelloService$$EnhancerByCGLIB$$be45efdd var10000 = new HelloService$$EnhancerByCGLIB$$be45efdd();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
CGLIB$SET_THREAD_CALLBACKS(var3);
HelloService$$EnhancerByCGLIB$$be45efdd var10000 = new HelloService$$EnhancerByCGLIB$$be45efdd;
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();
}
}
重点关注代理对象的sayHello方法:
从代理对象反编译源码可以知道,代理对象继承于HelloService,拦截器调用intercept()方法,
intercept()方法由自定义MyMethodInterceptor实现,所以,最后调用MyMethodInterceptor中
的intercept()方法,从而完成了由代理对象访问到目标对象的动态代理实现。
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