JDK动态代理和 CGLIB 代理

JDK动态代理和 CGLIB 代理

JDK动态代理：其代理对象必须是某个接口的实现，它是通过在运行期期间创建一个接口的实现类来完成对目标对象的代理。

代码示例

接口

public interface IUserDao {
    void save();
}

实现类

public class UserDao implements IUserDao {

    @Override
    public void save() {
        System.out.println("=====已经保存数据=======");
    }
}

代理类

public class DynamicJdkProxy {
    /**
     * 维护一个目标对象
     */
    private Object target;

    public DynamicJdkProxy(Object target) {
        this.target = target;
    }

    /**
     * 给目标对象生成代理对象
     *
     * @return
     */
    public Object getProxyInstance() {
        return Proxy.newProxyInstance(
                target.getClass().getClassLoader(),
                target.getClass().getInterfaces(),
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        System.out.println("开始事务2");
                        //执行目标对象方法
                        Object returnValue = method.invoke(target, args);
                        System.out.println("提交事务2");
                        return returnValue;
                    }
                }
        );
    }
}

运行

        //生成相应的class文件
        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
        // 目标对象
        IUserDao target = new UserDao();
        // 【原始的类型 class com.example.learning.proxy.UserDao】
        System.out.println(target.getClass());

        // 给目标对象，创建代理对象
        IUserDao proxy = (IUserDao) new DynamicJdkProxy(target).getProxyInstance();
        // class $Proxy0   内存中动态生成的代理对象
        System.out.println(proxy.getClass());

        // 执行方法   【代理对象】
        proxy.save();

执行结果

class com.example.learning.proxy.UserDao
class com.sun.proxy.$Proxy0
开始事务2
=====已经保存数据=======
提交事务2

Process finished with exit code 0

源码分析:

 public static Object newProxyInstance(ClassLoader loader,
                                          Class[] interfaces,
                                          InvocationHandler h)
        throws IllegalArgumentException
    {

        //克隆接口
        final Class[] intfs = interfaces.clone();
        //重点：生成 $Proxy0.class 文件并通过 ClassLoader 加载进来
        Class cl = getProxyClass0(loader, intfs);
        //创建代理类的构造器
        final Constructor cons = cl.getConstructor(constructorParams);
        //生成代理类的实例
        return cons.newInstance(new Object[]{h});

    }

再来看 getProxyClass0 的具体实现：ProxyClassFactory工厂类：

    Map, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
            for (Class intf : interfaces) {
                    interfaceClass = Class.forName(intf.getName(), false, loader);
            }

            String proxyPkg = null;     // package to define proxy class in

            //如果需要代理的类中有非public函数,直接取代理类的路径
            for (Class intf : interfaces) {
                int flags = intf.getModifiers();
                if (!Modifier.isPublic(flags)) {
                    accessFlags = Modifier.FINAL;
                    String name = intf.getName();
                    int n = name.lastIndexOf('.');
                    String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
                    if (proxyPkg == null) {
                        proxyPkg = pkg;
                    } else if (!pkg.equals(proxyPkg)) {
                        throw new IllegalArgumentException(
                            "non-public interfaces from different packages");
                    }
                }
            }
            
            //如果全是 Public 函数,取com.sun.proxy 作为包名
            if (proxyPkg == null) {
                // if no non-public proxy interfaces, use com.sun.proxy package
                proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
            }

            /*
             *  生成代理类名称 com.sun.proxy.$ProxyXXX
             */
            long num = nextUniqueNumber.getAndIncrement();
            String proxyName = proxyPkg + proxyClassNamePrefix + num;

            /*
             * 产生代理类class
             */
            byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces, accessFlags);
            //加载class
           return defineClass0(loader, proxyName,
                                    proxyClassFile, 0, proxyClassFile.length);
        }

生成class

    public static byte[] generateProxyClass(final String var0, Class[] var1, int var2) {
        ProxyGenerator var3 = new ProxyGenerator(var0, var1, var2);
        final byte[] var4 = var3.generateClassFile();
        if (saveGeneratedFiles) {
        ...
        }

是否生成class标识

private static final boolean saveGeneratedFiles = 
(Boolean)AccessController.doPrivileged(new GetBooleanAction("sun.misc.ProxyGenerator.saveGeneratedFiles"));

生成后的代理类:

public final class $Proxy0 extends Proxy implements IUserDao {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        //省略
    }

    public final void save() throws  {
        try {
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String toString() throws  {
        //省略
    }

    public final int hashCode() throws  {
        //省略
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("com.example.learning.proxy.IUserDao").getMethod("save");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

核心代码

调用的就是InvocationHandler#invoke方法
 super.h.invoke(this, m3, (Object[])null);
 
 h为Proxy类的
   /**
     * the invocation handler for this proxy instance.
     * @serial
     */
    protected InvocationHandler h;

JDK 代理通过在运行期期间创建一个接口的实现类来完成对目标对象的代理.

CGLIB 代理

CGLIB代理：实现原理类似于JDK动态代理，只是它在运行期间生成的代理对象是针对目标类扩展的子类。CGLIB是高效的代码生成包，底层依靠ASM（开源的Java字节码编辑类库）操作字节码实现。

代理类

public class UserDaoCG {
    public void save() {
        System.out.println("=====已经保存数据=======");
    }
}

CG 代理

public class CgLibProxy implements MethodInterceptor {
    /**
     * 维护目标对象
     */
    private Object target;

    public CgLibProxy(Object target) {
        this.target = target;
    }

    /**
     * 给目标对象创建一个代理对象
     *
     * @return
     */
    public Object getProxyInstance() {
        //1.工具类
        Enhancer en = new Enhancer();
        //2.设置父类
        en.setSuperclass(target.getClass());
        //3.设置回调函数
        en.setCallback(this);
        //4.创建子类(代理对象)
        return en.create();

    }

    @Override
    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
        System.out.println("开始CGLib事务...");

        //执行目标对象的方法
        Object returnValue = method.invoke(target, args);

        System.out.println("提交CGLib事务...");

        return returnValue;
    }
}

运行代理

        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "/Users/xxx/IdeaProjects/learning/cg");
        //目标对象
        UserDao target = new UserDao();

        //代理对象
        UserDao proxy = (UserDao) new CgLibProxy(target).getProxyInstance();

        //执行代理对象的方法
        proxy.save();

运行结果

CGLIB debugging enabled, writing to '/Users/xxx/IdeaProjects/learning/cg'
开始CGLib事务...
=====已经保存数据=======
提交CGLib事务...

生成的代理类

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.example.learning.proxy;

import java.lang.reflect.Method;
import org.springframework.cglib.core.ReflectUtils;
import org.springframework.cglib.core.Signature;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

public class UserDao$$EnhancerByCGLIB$$6efc5e8b extends UserDao 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$save$0$Method;
    private static final MethodProxy CGLIB$save$0$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.example.learning.proxy.UserDao$$EnhancerByCGLIB$$6efc5e8b");
        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$4");
        CGLIB$save$0$Method = ReflectUtils.findMethods(new String[]{"save", "()V"}, (var1 = Class.forName("com.example.learning.proxy.UserDao")).getDeclaredMethods())[0];
        CGLIB$save$0$Proxy = MethodProxy.create(var1, var0, "()V", "save", "CGLIB$save$0");
    }

    final void CGLIB$save$0() {
        super.save();
    }

    public final void save() {
        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$save$0$Method, CGLIB$emptyArgs, CGLIB$save$0$Proxy);
        } else {
            super.save();
        }
    }

    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 1826985398:
            if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                return CGLIB$equals$1$Proxy;
            }
            break;
        case 1872760024:
            if (var10000.equals("save()V")) {
                return CGLIB$save$0$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 UserDao$$EnhancerByCGLIB$$6efc5e8b() {
        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) {
        UserDao$$EnhancerByCGLIB$$6efc5e8b var1 = (UserDao$$EnhancerByCGLIB$$6efc5e8b)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);
        UserDao$$EnhancerByCGLIB$$6efc5e8b var10000 = new UserDao$$EnhancerByCGLIB$$6efc5e8b();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        UserDao$$EnhancerByCGLIB$$6efc5e8b var10000 = new UserDao$$EnhancerByCGLIB$$6efc5e8b();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        UserDao$$EnhancerByCGLIB$$6efc5e8b var10000 = new UserDao$$EnhancerByCGLIB$$6efc5e8b;
        switch(var1.length) {
        case 0:
            var10000.();
            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();
    }
}

关键代码

 public final void save() {
        //代理类
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (var10000 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }
        //如果代理类不为空,直接调用代理方法
        if (var10000 != null) {
            var10000.intercept(this, CGLIB$save$0$Method, CGLIB$emptyArgs, CGLIB$save$0$Proxy);
        } else {
            super.save();
        }
    }

由此可见:
运行期间生成的代理对象是针对目标类扩展的子类

在平时应用中,JDK 的动态代理要求代理的类必须有接口,这个限制了他的部分应用, 而 CGLIB
用继承的方式代理,摆脱了这个限制.

Spring 默认的代理为 CGLIB