Java基础-Cglib动态代理
摘自OSCHINA（开源中国）的介绍：CGLib (Code Generation Library) 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 字节码的动态生成。CGLib 比 Java 的 java.lang.reflect.Proxy 类更强的在于它不仅可以接管接口类的方法，还可以接管普通类
文章共9,691字 · 阅读需要大约33分钟
一键AI生成摘要，助你高效阅读
问答
·
摘自OSCHINA（开源中国）的介绍：
CGLib (Code Generation Library) 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 字节码的动态生成。CGLib 比 Java 的 java.lang.reflect.Proxy 类更强的在于它不仅可以接管接口类的方法，还可以接管普通类的方法。
CGLib 的底层是 Java 字节码操作框架 —— ASM。
Cglib动态代理的简单示例
1、引入Cglib的maven依赖：
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.3.0</version>
</dependency>
2、定义一个目标类，也就是被代理类，此时是一个图书管理员类，管理一些Book类对象（Book类为简单实体类，此处不贴代码）。
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("这里是 " + this.getClass().getName() + " 的getBook方法");
return books.getOrDefault(name, null);
}
}
3、定义一个代理工厂类，用来创建代理对象：
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代理基于创建子类重写父类方法实现，所以这里要确定父类，也就是被代理类。
Class<?> superClass = targetObject.getClass();
enhancer.setSuperclass(superClass);
/*
创建了一个MethodInterceptor拦截器接口的实现类对象，重写intercept回调方法，
参数依次为：代理对象、代理方法、方法参数、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("这是前置增强");
Object res = methodProxy.invokeSuper(o, objects);
System.out.println("这是后置增强");
return res;
}
};
enhancer.setCallback(interceptor);
return enhancer.create();
}
public static void main(String[] args) {
//这里设置一个系统属性，保存Cglib动态代理类的字节码文件
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "target/classes");
//创建原始对象
Librarian librarian = new Librarian("LiLei", 18);
Book book = new Book();
book.setBookName("钢铁是怎样炼成的");
librarian.addBook(book);
librarian.getBook("111");
//创建代理对象
CglibProxyFactory cglibProxyFactory = new CglibProxyFactory();
Librarian librarianProxy = (Librarian) cglibProxyFactory.getProxy(librarian);
librarianProxy.getBook("111");
}
}
运行结果如下：
原理
沿着enhancer.create()方法一直往下debug，会走到Enhancer类的generate(ClassLoaderData data)方法中，该方法返回的是代理类的Class
对象。
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;
//这里拿到一个Enhancer$EnhancerFactoryData对象，包括代理类Class对象、构造器等信息。
Object obj = data.get(this, getUseCache());
if (obj instanceof Class) {
return firstInstance((Class) obj);
}
//使用拿到的Enhancer$EnhancerFactoryData对象，实例化代理类对象。
return nextInstance(obj);
} catch (RuntimeException e) {
throw e;
} catch (Error e) {
throw e;
} catch (Exception e) {
throw new CodeGenerationException(e);
}
}
1）沿着data.get(this, getUseCache())方法往下走，一直到Enhancer父类的generate(ClassLoaderData data)方法中，就是该方法生成了代理类的Class
对象。
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
}
}
//结合当前Enhancer及父类信息生成代理类字节码
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 {
/*
内部调用了ClassLoader类的defineClass方法，将字节码转化成类的Class实例，然后调用Class.forName（初始化参数设置为
true）强制初始化。
*/
gen = ReflectUtils.defineClass(className, b, classLoader, protectionDomain);
}
}
//返回代理类Class对象
return gen;
} catch (RuntimeException e) {
throw e;
} catch (Error e) {
throw e;
} catch (Exception e) {
throw new CodeGenerationException(e);
} finally {
CURRENT.set(save);
}
}
包装后得到的Enhancer$EnhancerFactoryData对象结构：
2）再看nextInstance(obj)方法，这里最终使用构造器的newInstance方法实例化了代理对象。
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
//使用构造器的newInstance方法实例化代理对象。
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);
}
}
最后看看代理类的字节码文件：
Librarian
E
n
h
a
n
c
e
r
B
y
C
G
L
I
B
EnhancerByCGLIB
EnhancerByCGLIBe9192983字节码反编译后的代码如下：
//
// 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();
}
}
可以看到在代理类的重写方法中，使用了MethodInterceptor拦截器的intercept方法。
旨在为数千万中国开发者提供一个无缝且高效的云端环境，以支持学习、使用和贡献开源项目。
更多推荐
0
0- 0
已为社区贡献3条内容
所有评论(0)