Java中的Cglib動(dòng)態(tài)代理詳細(xì)解讀
前言
摘自O(shè)SCHINA(開(kāi)源中國(guó))的介紹:
CGLib (Code Generation Library) 是一個(gè)強(qiáng)大的、高性能、高質(zhì)量的 Code 生成類(lèi)庫(kù)。它可以在運(yùn)行期擴(kuò)展 Java 類(lèi)與實(shí)現(xiàn) Java 接口。Hibernate 用它來(lái)實(shí)現(xiàn) PO 字節(jié)碼的動(dòng)態(tài)生成。
CGLib 比 Java 的 java.lang.reflect.Proxy 類(lèi)更強(qiáng)的在于它不僅可以接管接口類(lèi)的方法,還可以接管普通類(lèi)的方法。 CGLib 的底層是 Java 字節(jié)碼操作框架 —— ASM。
Cglib動(dòng)態(tài)代理的簡(jiǎn)單示例
1、引入Cglib的maven依賴(lài):
<dependency> <groupId>cglib</groupId> <artifactId>cglib</artifactId> <version>3.3.0</version> </dependency>
2、定義一個(gè)目標(biāo)類(lèi),也就是被代理類(lèi),此時(shí)是一個(gè)圖書(shū)管理員類(lèi),管理一些Book類(lèi)對(duì)象(Book類(lèi)為簡(jiǎn)單實(shí)體類(lèi),此處不貼代碼)。
package org.example.proxy.cglib; import org.example.domain.Book; import java.util.HashMap; import java.util.Map; public class Librarian { private Map<String, Book> books = new HashMap<>(); public void addBook(Book book) { String name = book.getBookName(); if (!books.containsKey(name)) { books.put(name, book); } } public Book getBook(String name) { System.out.println("這里是 " + this.getClass().getName() + " 的getBook方法"); return books.getOrDefault(name, null); } }
3、定義一個(gè)代理工廠類(lèi),用來(lái)創(chuàng)建代理對(duì)象:
package org.example.proxy.cglib; import net.sf.cglib.core.DebuggingClassWriter; import net.sf.cglib.proxy.Enhancer; import net.sf.cglib.proxy.MethodInterceptor; import net.sf.cglib.proxy.MethodProxy; import org.example.domain.Book; import java.lang.reflect.Method; public class CglibProxyFactory { public Object getProxy(Object targetObject) { Enhancer enhancer = new Enhancer(); //Cglib代理基于創(chuàng)建子類(lèi)重寫(xiě)父類(lèi)方法實(shí)現(xiàn),所以這里要確定父類(lèi),也就是被代理類(lèi)。 Class<?> superClass = targetObject.getClass(); enhancer.setSuperclass(superClass); /* 創(chuàng)建了一個(gè)MethodInterceptor攔截器接口的實(shí)現(xiàn)類(lèi)對(duì)象,重寫(xiě)intercept回調(diào)方法, 參數(shù)依次為:代理對(duì)象、代理方法、方法參數(shù)、方法代理 */ MethodInterceptor interceptor = new MethodInterceptor() { @Override public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable { System.out.println("這是前置增強(qiáng)"); Object res = methodProxy.invokeSuper(o, objects); System.out.println("這是后置增強(qiáng)"); return res; } }; enhancer.setCallback(interceptor); return enhancer.create(); } public static void main(String[] args) { //這里設(shè)置一個(gè)系統(tǒng)屬性,保存Cglib動(dòng)態(tài)代理類(lèi)的字節(jié)碼文件 System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "target/classes"); //創(chuàng)建原始對(duì)象 Librarian librarian = new Librarian("LiLei", 18); Book book = new Book(); book.setBookName("鋼鐵是怎樣煉成的"); librarian.addBook(book); librarian.getBook("111"); //創(chuàng)建代理對(duì)象 CglibProxyFactory cglibProxyFactory = new CglibProxyFactory(); Librarian librarianProxy = (Librarian) cglibProxyFactory.getProxy(librarian); librarianProxy.getBook("111"); } }
運(yùn)行結(jié)果如下:
原理
沿著enhancer.create()方法一直往下debug,會(huì)走到Enhancer類(lèi)的generate(ClassLoaderData data)方法中,該方法返回的是代理類(lèi)的Class 對(duì)象。
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; //這里拿到一個(gè)Enhancer$EnhancerFactoryData對(duì)象,包括代理類(lèi)Class對(duì)象、構(gòu)造器等信息。 Object obj = data.get(this, getUseCache()); if (obj instanceof Class) { return firstInstance((Class) obj); } //使用拿到的Enhancer$EnhancerFactoryData對(duì)象,實(shí)例化代理類(lèi)對(duì)象。 return nextInstance(obj); } catch (RuntimeException e) { throw e; } catch (Error e) { throw e; } catch (Exception e) { throw new CodeGenerationException(e); } }
1)沿著data.get(this, getUseCache())方法往下走,一直到Enhancer父類(lèi)的generate(ClassLoaderData data)方法中,就是該方法生成了代理類(lèi)的Class 對(duì)象。
protected Class generate(ClassLoaderData data) { Class gen; Object save = CURRENT.get(); CURRENT.set(this); try { ClassLoader classLoader = data.getClassLoader(); if (classLoader == null) { throw new IllegalStateException("ClassLoader is null while trying to define class " + getClassName() + ". It seems that the loader has been expired from a weak reference somehow. " + "Please file an issue at cglib's issue tracker."); } synchronized (classLoader) { String name = generateClassName(data.getUniqueNamePredicate()); data.reserveName(name); this.setClassName(name); } if (attemptLoad) { try { gen = classLoader.loadClass(getClassName()); return gen; } catch (ClassNotFoundException e) { // ignore } } //結(jié)合當(dāng)前Enhancer及父類(lèi)信息生成代理類(lèi)字節(jié)碼 byte[] b = strategy.generate(this); String className = ClassNameReader.getClassName(new ClassReader(b)); ProtectionDomain protectionDomain = getProtectionDomain(); synchronized (classLoader) { // just in case if (protectionDomain == null) { gen = ReflectUtils.defineClass(className, b, classLoader); } else { /* 內(nèi)部調(diào)用了ClassLoader類(lèi)的defineClass方法,將字節(jié)碼轉(zhuǎn)化成類(lèi)的Class實(shí)例,然后調(diào)用Class.forName(初始化參數(shù)設(shè)置為 true)強(qiáng)制初始化。 */ gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain); } } //返回代理類(lèi)Class對(duì)象 return gen; } catch (RuntimeException e) { throw e; } catch (Error e) { throw e; } catch (Exception e) { throw new CodeGenerationException(e); } finally { CURRENT.set(save); } }
包裝后得到的Enhancer$EnhancerFactoryData對(duì)象結(jié)構(gòu):
2)再看nextInstance(obj)方法,這里最終使用構(gòu)造器的newInstance方法實(shí)例化了代理對(duì)象。
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 //使用構(gòu)造器的newInstance方法實(shí)例化代理對(duì)象。 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); } }
最后看看代理類(lèi)的字節(jié)碼文件:
Librarian EnhancerByCGLIB 9192983字節(jié)碼反編譯后的代碼如下:
// // Source code recreated from a .class file by IntelliJ IDEA // (powered by FernFlower decompiler) // package org.example.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; import org.example.domain.Book; public class Librarian$$EnhancerByCGLIB$$e9192983 extends Librarian 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$addBook$0$Method; private static final MethodProxy CGLIB$addBook$0$Proxy; private static final Object[] CGLIB$emptyArgs; private static final Method CGLIB$getBook$1$Method; private static final MethodProxy CGLIB$getBook$1$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 var0 = Class.forName("org.example.proxy.cglib.Librarian$$EnhancerByCGLIB$$e9192983"); 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$2$Method = var10000[0]; CGLIB$equals$2$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2"); CGLIB$toString$3$Method = var10000[1]; CGLIB$toString$3$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$3"); CGLIB$hashCode$4$Method = var10000[2]; CGLIB$hashCode$4$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$4"); CGLIB$clone$5$Method = var10000[3]; CGLIB$clone$5$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5"); var10000 = ReflectUtils.findMethods(new String[]{"addBook", "(Lorg/example/domain/Book;)V", "getBook", "(Ljava/lang/String;)Lorg/example/domain/Book;"}, (var1 = Class.forName("org.example.proxy.cglib.Librarian")).getDeclaredMethods()); CGLIB$addBook$0$Method = var10000[0]; CGLIB$addBook$0$Proxy = MethodProxy.create(var1, var0, "(Lorg/example/domain/Book;)V", "addBook", "CGLIB$addBook$0"); CGLIB$getBook$1$Method = var10000[1]; CGLIB$getBook$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Lorg/example/domain/Book;", "getBook", "CGLIB$getBook$1"); } final void CGLIB$addBook$0(Book var1) { super.addBook(var1); } public final void addBook(Book var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { var10000.intercept(this, CGLIB$addBook$0$Method, new Object[]{var1}, CGLIB$addBook$0$Proxy); } else { super.addBook(var1); } } final Book CGLIB$getBook$1(String var1) { return super.getBook(var1); } public final Book getBook(String var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? (Book)var10000.intercept(this, CGLIB$getBook$1$Method, new Object[]{var1}, CGLIB$getBook$1$Proxy) : super.getBook(var1); } final boolean CGLIB$equals$2(Object var1) { return super.equals(var1); } public final boolean equals(Object var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var2 = var10000.intercept(this, CGLIB$equals$2$Method, new Object[]{var1}, CGLIB$equals$2$Proxy); return var2 == null ? false : (Boolean)var2; } else { return super.equals(var1); } } final String CGLIB$toString$3() { return super.toString(); } public final String toString() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$3$Method, CGLIB$emptyArgs, CGLIB$toString$3$Proxy) : super.toString(); } final int CGLIB$hashCode$4() { return super.hashCode(); } public final int hashCode() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var1 = var10000.intercept(this, CGLIB$hashCode$4$Method, CGLIB$emptyArgs, CGLIB$hashCode$4$Proxy); return var1 == null ? 0 : ((Number)var1).intValue(); } else { return super.hashCode(); } } final Object CGLIB$clone$5() throws CloneNotSupportedException { return super.clone(); } protected final Object clone() throws CloneNotSupportedException { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (var10000 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? var10000.intercept(this, CGLIB$clone$5$Method, CGLIB$emptyArgs, CGLIB$clone$5$Proxy) : super.clone(); } public static MethodProxy CGLIB$findMethodProxy(Signature var0) { String var10000 = var0.toString(); switch (var10000.hashCode()) { case -1644681230: if (var10000.equals("addBook(Lorg/example/domain/Book;)V")) { return CGLIB$addBook$0$Proxy; } break; case -508378822: if (var10000.equals("clone()Ljava/lang/Object;")) { return CGLIB$clone$5$Proxy; } break; case 1332997645: if (var10000.equals("getBook(Ljava/lang/String;)Lorg/example/domain/Book;")) { return CGLIB$getBook$1$Proxy; } break; case 1826985398: if (var10000.equals("equals(Ljava/lang/Object;)Z")) { return CGLIB$equals$2$Proxy; } break; case 1913648695: if (var10000.equals("toString()Ljava/lang/String;")) { return CGLIB$toString$3$Proxy; } break; case 1984935277: if (var10000.equals("hashCode()I")) { return CGLIB$hashCode$4$Proxy; } } return null; } public Librarian$$EnhancerByCGLIB$$e9192983() { 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) { Librarian$$EnhancerByCGLIB$$e9192983 var1 = (Librarian$$EnhancerByCGLIB$$e9192983)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); Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Callback var1) { CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1}); Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) { CGLIB$SET_THREAD_CALLBACKS(var3); Librarian$$EnhancerByCGLIB$$e9192983 var10000 = new Librarian$$EnhancerByCGLIB$$e9192983; 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(); } }
可以看到在代理類(lèi)的重寫(xiě)方法中,使用了MethodInterceptor攔截器的intercept方法。
到此這篇關(guān)于Java中的Cglib動(dòng)態(tài)代理詳細(xì)解讀的文章就介紹到這了,更多相關(guān)Cglib動(dòng)態(tài)代理內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家!
- Java兩種動(dòng)態(tài)代理JDK動(dòng)態(tài)代理和CGLIB動(dòng)態(tài)代理詳解
- Java的動(dòng)態(tài)代理模式之Cglib代理詳解
- Java的CGLIB動(dòng)態(tài)代理深入解析
- Java的Cglib動(dòng)態(tài)代理實(shí)現(xiàn)方式詳解
- Java中的CGLIB動(dòng)態(tài)代理的使用及原理詳解
- Spring之AOP兩種代理機(jī)制對(duì)比分析(JDK和CGLib動(dòng)態(tài)代理)
- 基于jdk動(dòng)態(tài)代理和cglib動(dòng)態(tài)代理實(shí)現(xiàn)及區(qū)別說(shuō)明
- Java JDK與cglib動(dòng)態(tài)代理有什么區(qū)別
相關(guān)文章
springboot+Oauth2實(shí)現(xiàn)自定義AuthenticationManager和認(rèn)證path
本篇文章主要介紹了springboot+Oauth2實(shí)現(xiàn)自定義AuthenticationManager和認(rèn)證path,具有一定的參考價(jià)值,感興趣的小伙伴們可以參考一下2017-09-09Java中的System.getenv()和System.getProperty()使用詳解
文章介紹了Java中用于讀取環(huán)境配置信息的兩種方法:System.getenv()和System.getProperty(),前者讀取系統(tǒng)環(huán)境變量,返回一個(gè)不可修改的Map;后者獲取JVM環(huán)境變量值,可以通過(guò)-D參數(shù)設(shè)置,文章還提到,通過(guò)這兩種方法可以簡(jiǎn)化配置,不需要修改代碼2024-11-11Mybatis?Plus?中的LambdaQueryWrapper示例詳解
這篇文章主要介紹了Mybatis?Plus?中的LambdaQueryWrapper,本文通過(guò)示例代碼給大家介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值,需要的朋友可以參考下2022-03-03Java實(shí)現(xiàn)lucene搜索功能的方法(推薦)
下面小編就為大家?guī)?lái)一篇Java實(shí)現(xiàn)lucene搜索功能的方法(推薦)。小編覺(jué)得挺不錯(cuò)的,現(xiàn)在就分享給大家,也給大家做個(gè)參考。一起跟隨小編過(guò)來(lái)看看吧2016-12-12