Java中的Cglib動態(tài)代理詳細解讀
更新時間：2023年11月28日 10:23:45 作者：后仰大風車
這篇文章主要介紹了Java中的Cglib動態(tài)代理詳細解讀,CGLib是一個強大的、高性能、高質量的 Code 生成類庫,它可以在運行期擴展 Java 類與實現 Java 接口,需要的朋友可以參考下
前言
摘自OSCHINA（開源中國）的介紹：
CGLib (Code Generation Library) 是一個強大的、高性能、高質量的 Code 生成類庫。它可以在運行期擴展 Java 類與實現 Java 接口。Hibernate 用它來實現 PO 字節(jié)碼的動態(tài)生成。
CGLib 比 Java 的 java.lang.reflect.Proxy 類更強的在于它不僅可以接管接口類的方法，還可以接管普通類的方法。 CGLib 的底層是 Java 字節(jié)碼操作框架 —— ASM。
Cglib動態(tài)代理的簡單示例
1、引入Cglib的maven依賴：
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.3.0</version>
</dependency>
2、定義一個目標類，也就是被代理類，此時是一個圖書管理員類，管理一些Book類對象（Book類為簡單實體類，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、定義一個代理工廠類，用來創(chuàng)建代理對象：
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)建子類重寫父類方法實現，所以這里要確定父類，也就是被代理類。
Class<?> superClass = targetObject.getClass();
enhancer.setSuperclass(superClass);
/*
創(chuàng)建了一個MethodInterceptor攔截器接口的實現類對象，重寫intercept回調方法，
參數依次為：代理對象、代理方法、方法參數、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");
Object res = methodProxy.invokeSuper(o, objects);
System.out.println("這是后置增強");
return res;
}
};
enhancer.setCallback(interceptor);
return enhancer.create();
}
public static void main(String[] args) {
//這里設置一個系統屬性，保存Cglib動態(tài)代理類的字節(jié)碼文件
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "target/classes");
//創(chuàng)建原始對象
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)建代理對象
CglibProxyFactory cglibProxyFactory = new CglibProxyFactory();
Librarian librarianProxy = (Librarian) cglibProxyFactory.getProxy(librarian);
librarianProxy.getBook("111");
}
}
運行結果如下：
原理
沿著enhancer.create()方法一直往下debug，會走到Enhancer類的generate(ClassLoaderData data)方法中，該方法返回的是代理類的Class 對象。
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Enhancer$EnhancerFactoryData對象，包括代理類Class對象、構造器等信息。
Object obj = data.get(this, getUseCache());
if (obj instanceof Class) {
return firstInstance((Class) obj);
}
//使用拿到的Enhancer$EnhancerFactoryData對象，實例化代理類對象。
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父類的generate(ClassLoaderData data)方法中，就是該方法生成了代理類的Class 對象。
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
}
}
//結合當前Enhancer及父類信息生成代理類字節(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 {
/*
內部調用了ClassLoader類的defineClass方法，將字節(jié)碼轉化成類的Class實例，然后調用Class.forName（初始化參數設置為
true）強制初始化。
*/
gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain);
}
}
//返回代理類Class對象
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對象結構：
2）再看nextInstance(obj)方法，這里最終使用構造器的newInstance方法實例化了代理對象。
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
//使用構造器的newInstance方法實例化代理對象。
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();
}
}可以看到在代理類的重寫方法中，使用了MethodInterceptor攔截器的intercept方法。
到此這篇關于Java中的Cglib動態(tài)代理詳細解讀的文章就介紹到這了,更多相關Cglib動態(tài)代理內容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關文章希望大家以后多多支持腳本之家！
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