从动态代理商实现到Spring AOP看这一篇就够了

代理商是一种设计模式，目的是对外提供统一的接口（这样可以隐藏被代理商类不想公开的方法），在此基础上，可以在代理商类实现逻辑中加入少量附加操作，做少量加强解决，该方式不会影响被代理商类的原实现。

代理商分为静态代理商和动态代理商两种，静态代理商就是在代理商类内部持有被代理商对象的引用，这种方式很直接，但需要hard coding，不易扩展，无法做统一解决。

动态代理商主要有jdk提供的Proxy、Cglib以及Javassist，其中Javassist主要是一套字节码操作库，有两种使用方式，既可以有相似Cglib的用法，也可以根据字节码结构去动态生成类，本文主要讲述Proxy和Cglib。

动态代理商在Spring、Mybatis、Dubbo等各大框架中均有大量使用，因而熟习动态代理商是阅读这些框架源码必需掌握的基本功之一

Proxy是根据接口生成代理商类，生成的代理商类实现了被代理商类的接口，Cglib是生成被代理商类的子类，因而被代理商类不能为final，而且必需有无参构造函数。

Proxy

Proxy需要写一个实现InvocationHandler（实现invoke方法）的代理商类（以下称Agency），注意Agency不是最后生成的动态代理商类，动态代理商类是Proxy.newProxyInstance过程中生成的，newProxyInstance方法会为动态代理商类newInstance一个实例对象，动态代理商类的主要思想是调用agency 对象（Agency类的实例）的invoke方法，在invoke方法中再通过反射调用被代理商对象的方法，添加附加解决。
上代码：

interface Subject {    void doSomething();}interface DupSubject {    void doSomethingAgain();}class Real implements Subject, DupSubject {    public void doSomething() {        System.out.println("=========Real doSomething=========");    }    @Override    public void doSomethingAgain() {        System.out.println("=========Real doSomethingAgain=========");    }}class Agency implements InvocationHandler {    private Real sub;    public Object bind(Real sub) {        this.sub = sub;        Object obj = Proxy.newProxyInstance(Test.class.getClassLoader(), sub.getClass().getInterfaces(), this);        return obj;    }    @Override    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {        // 前置加强解决        System.out.println("+++++++++Agency begin+++++++");        method.invoke(sub, args);        // 后置加强解决        System.out.println("+++++++++Agency end+++++++");        return null;    }}public class Test {    public static void main(String[] args) {        // 设置系统参数，输出动态生成的代理商类        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");        Agency agency = new Agency();        Real real = new Real();        // 绑定被代理商对象，返回代理商对象        Object obj = agency.bind(real);        Subject sub = (Subject) (obj);        sub.doSomething();        DupSubject dubSub = (DupSubject) (obj);        dubSub.doSomethingAgain();    }}

程序输出内容为：

+++++++++Agency begin+++++++=========Real doSomething=========+++++++++Agency end++++++++++++++++Agency begin+++++++=========Real doSomethingAgain=========+++++++++Agency end+++++++

上生成的动态代理商类：

// 默认继承Proxy类且实现被代理商类的所有接口final class $Proxy0 extends Proxy implements Subject, DupSubject {    private static Method m1;    private static Method m3;    private static Method m2;    private static Method m4;    private static Method m0;        // 将所有method对象在初始加载代理商类时缓存下来，防止每次都通过反射获取    static {        try {            m3 = Class.forName("Subject").getMethod("doSomething", new Class[0]);            m4 = Class.forName("DupSubject").getMethod("doSomethingAgain", new Class[0]);            // 省略toString/equals/hashcode等方法            ...        } catch (NoSuchMethodException nosuchmethodexception) {            throw new NoSuchMethodError(nosuchmethodexception.getMessage());        } catch (ClassNotFoundException classnotfoundexception) {            throw new NoClassDefFoundError(classnotfoundexception.getMessage());        }    }    public $Proxy0(InvocationHandler invocationhandler) {        // 向super类也就是proxy类传入InvocationHandler对象        super(invocationhandler);    }        // 直接调用了之前传入的InvocationHandler对象的invoke方法    public final void doSomething() {        try {            super.h.invoke(this, m3, null);            return;        } catch (Error) {        } catch (Throwable throwable) {            throw new UndeclaredThrowableException(throwable);        }    }        // 直接调用了之前传入的InvocationHandler对象的invoke方法    public final void doSomethingAgain() {        try {            super.h.invoke(this, m4, null);            return;        } catch (Error) {        } catch (Throwable throwable) {            throw new UndeclaredThrowableException(throwable);        }    }}

动态代理商类是如何生成的具体参照ProxyGenerator的 generateClassFile方法，该方法先为代理商类增加equals/hashcode/toString方法，而后添加被代理商类接口的所有方法，解决过程主要为通过反射获取被代理商方法的方法名、参数类型、返回值类型、异常类型，而后生成根据以上参数生成代理商方法的字节码内容（字节码实现一个事：即调用属性InvocationHandler对象的invoke方法），看这个方法可以充分了解class文件的组成，即常量池、字段表、方法表等。

注意：proxy方法之间的内部调用是不走invoke逻辑的

Cglib

上代码：

interface Subject {    void doSomething();}interface AnotherSubject {    void doSomethingAgain();}class Real implements Subject, AnotherSubject {    @Override    public void doSomething() {        System.out.println("=========Real doSomething=========");    }    @Override    public void doSomethingAgain() {        System.out.println("=========Real doSomethingAgain begin====");        // 调用内部方法，注意invokeSuper时该调用能否会进入加强逻辑        this.doSomething();        System.out.println("=========Real doSomethingAgain end====");    }}class Agency implements MethodInterceptor {    private Object target;        // 持有被代理商对象    public Agency(Object target) {        this.target = target;    }    @Override    // obj对象为动态代理商类的实例    // method为被代理商类的方法    // methodProxy持有被代理商方法、代理商方法、被代理商类、代理商类以及方法的index索引    public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {        System.out.println("+++++++++Agency begin+++++++");        // 直接调用被代理商对象的方法        method.invoke(target, args);        // 调用methodProxy的invokeSuper方法，注意假如调用methodProxy的invoke方法        // 由于传入的obj为动态代理商对象，则会陷入死循环，假如为被代理商对象target，则不会        proxy.invokeSuper(obj, args);        System.out.println("+++++++++Agency end+++++++");        return null;    }}public class Test {    public static void main(String[] args) {        // 设置系统参数，输出动态生成的代理商类        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "E:/temp/dymamicCode");        Real real = new Real();        Agency agency = new Agency(real);        Enhancer enhancer = new Enhancer();        // 设置被代理商类        enhancer.setSuperclass(real.getClass());        // 设置回调MethodInterceptor对象        enhancer.setCallback(agency);        Real proxy = (Real)enhancer.create();        proxy.doSomething();        proxy.doSomethingAgain();    }}

程序输出结果为：

+++++++++Agency begin+++++++=========Real doSomething==================Real doSomething=========+++++++++Agency end++++++++++++++++Agency begin+++++++// method.invoke 内容 begin=========Real doSomethingAgain begin=============Real doSomething==================Real doSomethingAgain end====// method.invoke 内容 end// methodProxy invokeSuper 内容 begin=========Real doSomethingAgain begin====// 传入的obj是动态代理商类实例，因而内部调用的this为动态代理商类实例，进入加强逻辑+++++++++Agency begin+++++++=========Real doSomething==================Real doSomething=========+++++++++Agency end+++++++=========Real doSomethingAgain end====// methodProxy invokeSuper 内容 end+++++++++Agency end+++++++

上生成的动态代理商类，主要有三个类，在生成fastclass过程中还有少量附加类:

• 生成的动态代理商类

// 默认实现Factory接口，继承被代理商类public class Real$$EnhancerByCGLIB$$148ae4e extends Real 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;    // MethodInterceptor对象，即callback    private MethodInterceptor CGLIB$CALLBACK_0;    // 样例没有实现filter，通过filter去过滤callback    private static Object CGLIB$CALLBACK_FILTER;    private static final Method CGLIB$doSomething$0$Method;    private static final MethodProxy CGLIB$doSomething$0$Proxy;    private static final Object[] CGLIB$emptyArgs;    private static final Method CGLIB$doSomethingAgain$1$Method;    private static final MethodProxy CGLIB$doSomethingAgain$1$Proxy;    // 略去equals/hashcode等方法    ...        // 为了方便阅读，将该static块提前    static {        CGLIB$STATICHOOK1();    }        static void CGLIB$STATICHOOK1() {        CGLIB$THREAD_CALLBACKS = new ThreadLocal();        CGLIB$emptyArgs = new Object[0];        // var0为代理商类        Class var0 = Class.forName("Real$$EnhancerByCGLIB$$148ae4e");        // var1为被代理商类        Class var1;        // var10000持有所有的被代理商方法        Method[] var10000 = ReflectUtils.findMethods(new String[]{"doSomething", "()V", "doSomethingAgain", "()V"}, (var1 = Class.forName("Real")).getDeclaredMethods());        // CGLIB$doSomething$0$Method为被代理商方法doSomething        CGLIB$doSomething$0$Method = var10000[0];        // doSomething的MethodProxy        CGLIB$doSomething$0$Proxy = MethodProxy.create(var1, var0, "()V", "doSomething", "CGLIB$doSomething$0");        CGLIB$doSomethingAgain$1$Method = var10000[1];        CGLIB$doSomethingAgain$1$Proxy = MethodProxy.create(var1, var0, "()V", "doSomethingAgain", "CGLIB$doSomethingAgain$1");        // 略去equals/hashcode等方法        ...    }        final void CGLIB$doSomething$0() {        super.doSomething();    }        // 代理商方法doSomething调用入口    public final void doSomething() {        // CGLIB$CALLBACK_0为MethodInterceptor对象        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;        if (this.CGLIB$CALLBACK_0 == null) {            CGLIB$BIND_CALLBACKS(this);            var10000 = this.CGLIB$CALLBACK_0;        }        if (var10000 != null) {            // 调用MethodInterceptor对象的intercept方法            // 重点看下调用传参：            // this为代理商对象实例，即Real$$EnhancerByCGLIB$$148ae4e类的实例            // CGLIB$doSomething$0$Method为被代理商方法doSomething            // CGLIB$emptyArgs 无参            // CGLIB$doSomething$0$Proxy为doSomething的methodProxy            var10000.intercept(this, CGLIB$doSomething$0$Method, CGLIB$emptyArgs, CGLIB$doSomething$0$Proxy);        } else {            super.doSomething();        }    }    final void CGLIB$doSomethingAgain$1() {        super.doSomethingAgain();    }        // 代理商方法doSomethingAgain调用入口    public final void doSomethingAgain() {        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;        if (this.CGLIB$CALLBACK_0 == null) {            CGLIB$BIND_CALLBACKS(this);            var10000 = this.CGLIB$CALLBACK_0;        }        if (var10000 != null) {            // 参数分析同上            var10000.intercept(this, CGLIB$doSomethingAgain$1$Method, CGLIB$emptyArgs, CGLIB$doSomethingAgain$1$Proxy);        } else {            super.doSomethingAgain();        }    }        // 略去equals/hashcode等方法   ...    public static MethodProxy CGLIB$findMethodProxy(Signature var0) {        String var10000 = var0.toString();        switch(var10000.hashCode()) {        case 516651364:            if (var10000.equals("doSomethingAgain()V")) {                return CGLIB$doSomethingAgain$1$Proxy;            }            break;        // 略去equals/hashcode等方法            ...        case 2121560294:            if (var10000.equals("doSomething()V")) {                return CGLIB$doSomething$0$Proxy;            }        }        return null;    }    public Real$$EnhancerByCGLIB$$148ae4e() {        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$STATIC_CALLBACKS = var0;    }        // 设置属性CGLIB$CALLBACK_0，即MethodInterceptor对象    private static final void CGLIB$BIND_CALLBACKS(Object var0) {        Real$$EnhancerByCGLIB$$148ae4e var1 = (Real$$EnhancerByCGLIB$$148ae4e)var0;        if (!var1.CGLIB$BOUND) {            var1.CGLIB$BOUND = true;            Object var10000 = CGLIB$THREAD_CALLBACKS.get();            if (var10000 == null) {                var10000 = CGLIB$STATIC_CALLBACKS;                if (CGLIB$STATIC_CALLBACKS == null) {                    return;                }            }            var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];        }    }        // 生成被代理商类实例    public Object newInstance(Callback[] var1) {        // 设置MethodInterceptor对象        CGLIB$SET_THREAD_CALLBACKS(var1);        Real$$EnhancerByCGLIB$$148ae4e var10000 = new Real$$EnhancerByCGLIB$$148ae4e();        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);        return var10000;    }        public Object newInstance(Callback var1) {        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});        Real$$EnhancerByCGLIB$$148ae4e var10000 = new Real$$EnhancerByCGLIB$$148ae4e();        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);        return var10000;    }    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {        CGLIB$SET_THREAD_CALLBACKS(var3);        Real$$EnhancerByCGLIB$$148ae4e var10000 = new Real$$EnhancerByCGLIB$$148ae4e;        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];    }}

生成上述class的方式可见Enhancer的generateClass方法
由上可见，最终调用methodInterceptor的intercept方法，该方法中进行加强解决，而后调用被代理商对象的相关方法，两种方式：

• method.invoke
• methodProxy.invokeSuper
  method.invoke就是直接调用被代理商方法，重点看看methodProxy的invokeSuper和invoke会发生什么？

public Object invokeSuper(Object obj, Object[] args) throws Throwable {    try {        // 初始化fastClass信息        this.init();        MethodProxy.FastClassInfo fci = this.fastClassInfo;        // obj为动态代理商对象 f2为代理商类的fastClass         // i2为该方法在fastClass的index        return fci.f2.invoke(fci.i2, obj, args);    ...}public Object invoke(Object obj, Object[] args) throws Throwable {    try {        this.init();        MethodProxy.FastClassInfo fci = this.fastClassInfo;        // obj为被代理商对象 f1为被代理商类的fastClass         // i1为该方法在fastClass的index        return fci.f1.invoke(fci.i1, obj, args);    ...}

都调用了init方法，该方法会初始化fastClassInfo，看看生成的fastClass的格式：

// 为被代理商类生成的FastClasspublic class Real$$FastClassByCGLIB$$26cdbe extends FastClass {    public Real$$FastClassByCGLIB$$26cdbe(Class var1) {        super(var1);    }        // 根据方法 name和desc获取index    public int getIndex(Signature var1) {        String var10000 = var1.toString();        switch(var10000.hashCode()) {        case 516651364:            if (var10000.equals("doSomethingAgain()V")) {                return 1;            }            break;        ...            case 2121560294:            if (var10000.equals("doSomething()V")) {                return 0;            }        }        return -1;    }    public int getIndex(String var1, Class[] var2) {        switch(var1.hashCode()) {        ...        case -1265074063:            if (var1.equals("doSomethingAgain")) {                switch(var2.length) {                case 0:                    return 1;                }            }            break;        case 1794410543:            if (var1.equals("doSomething")) {                switch(var2.length) {                case 0:                    return 0;                }            }        }        return -1;    }    public int getIndex(Class[] var1) {        switch(var1.length) {        case 0:            return 0;        default:            return -1;        }    }        // 根据index var1调用被代理商对象var2的方法    public Object invoke(int var1, Object var2, Object[] var3) throws InvocationTargetException {        Real var10000 = (Real)var2;        int var10001 = var1;        try {            switch(var10001) {            case 0:                var10000.doSomething();                return null;            case 1:                var10000.doSomethingAgain();                return null;            ...            }        } catch (Throwable var4) {            throw new InvocationTargetException(var4);        }        throw new IllegalArgumentException("Cannot find matching method/constructor");    }    public Object newInstance(int var1, Object[] var2) throws InvocationTargetException {        Real var10000 = new Real;        Real var10001 = var10000;        int var10002 = var1;        try {            switch(var10002) {            case 0:                var10001.<init>();                return var10000;            }        } catch (Throwable var3) {            throw new InvocationTargetException(var3);        }        throw new IllegalArgumentException("Cannot find matching method/constructor");    }    public int getMaxIndex() {        return 4;    }}// 为动态代理商类生成的fastClasspublic class Real$$EnhancerByCGLIB$$148ae4e$$FastClassByCGLIB$$1c2aeb82 extends FastClass {    public Real$$EnhancerByCGLIB$$148ae4e$$FastClassByCGLIB$$1c2aeb82(Class var1) {        super(var1);    }    public int getIndex(Signature var1) {        String var10000 = var1.toString();        switch(var10000.hashCode()) {        case -2055565910:            if (var10000.equals("CGLIB$SET_THREAD_CALLBACKS([Lnet/sf/cglib/proxy/Callback;)V")) {                return 14;            }            break;        case -1457535688:            if (var10000.equals("CGLIB$STATICHOOK1()V")) {                return 21;            }            break;        case -894172689:            if (var10000.equals("newInstance(Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {                return 6;            }            break;        case -713887907:            if (var10000.equals("CGLIB$doSomething$0()V")) {                return 22;            }            break;        case -623122092:            if (var10000.equals("CGLIB$findMethodProxy(Lnet/sf/cglib/core/Signature;)Lnet/sf/cglib/proxy/MethodProxy;")) {                return 20;            }            break;        case -419626537:            if (var10000.equals("setCallbacks([Lnet/sf/cglib/proxy/Callback;)V")) {                return 10;            }            break;        case 516651364:            if (var10000.equals("doSomethingAgain()V")) {                return 9;            }            break;        case 560567118:            if (var10000.equals("setCallback(ILnet/sf/cglib/proxy/Callback;)V")) {                return 7;            }            break;        case 811063227:            if (var10000.equals("newInstance([Ljava/lang/Class;[Ljava/lang/Object;[Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {                return 4;            }            break;        case 973717575:            if (var10000.equals("getCallbacks()[Lnet/sf/cglib/proxy/Callback;")) {                return 12;            }            break;        case 1132140820:            if (var10000.equals("CGLIB$doSomethingAgain$1()V")) {                return 15;            }            break;        case 1221173700:            if (var10000.equals("newInstance([Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {                return 5;            }            break;        case 1230699260:            if (var10000.equals("getCallback(I)Lnet/sf/cglib/proxy/Callback;")) {                return 11;            }            break;        case 1584330438:            if (var10000.equals("CGLIB$SET_STATIC_CALLBACKS([Lnet/sf/cglib/proxy/Callback;)V")) {                return 13;            }            break;        case 2121560294:            if (var10000.equals("doSomething()V")) {                return 8;            }        ...            }        return -1;    }        // 根据方法name和desc获取index    public int getIndex(String var1, Class[] var2) {        switch(var1.hashCode()) {        case -1549500735:            if (var1.equals("CGLIB$doSomethingAgain$1")) {                switch(var2.length) {                case 0:                    return 15;                }            }            break;        case -1265074063:            if (var1.equals("doSomethingAgain")) {                switch(var2.length) {                case 0:                    return 9;                }            }            break;        case -1053468136:            if (var1.equals("getCallbacks")) {                switch(var2.length) {                case 0:                    return 12;                }            }            break;        case -60403779:            if (var1.equals("CGLIB$SET_STATIC_CALLBACKS")) {                switch(var2.length) {                case 1:                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {                        return 13;                    }                }            }            break;        case 85179481:            if (var1.equals("CGLIB$SET_THREAD_CALLBACKS")) {                switch(var2.length) {                case 1:                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {                        return 14;                    }                }            }            break;        case 161998109:            if (var1.equals("CGLIB$STATICHOOK1")) {                switch(var2.length) {                case 0:                    return 21;                }            }            break;        case 180909336:            if (var1.equals("CGLIB$doSomething$0")) {                switch(var2.length) {                case 0:                    return 22;                }            }            break;        case 495524492:            if (var1.equals("setCallbacks")) {                switch(var2.length) {                case 1:                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {                        return 10;                    }                }            }            break;        case 1154623345:            if (var1.equals("CGLIB$findMethodProxy")) {                switch(var2.length) {                case 1:                    if (var2[0].getName().equals("net.sf.cglib.core.Signature")) {                        return 20;                    }                }            }            break;        case 1794410543:            if (var1.equals("doSomething")) {                switch(var2.length) {                case 0:                    return 8;                }            }            break;        case 1811874389:            if (var1.equals("newInstance")) {                switch(var2.length) {                case 1:                    String var10001 = var2[0].getName();                    switch(var10001.hashCode()) {                    case -845341380:                        if (var10001.equals("net.sf.cglib.proxy.Callback")) {                            return 6;                        }                        break;                    case 1730110032:                        if (var10001.equals("[Lnet.sf.cglib.proxy.Callback;")) {                            return 5;                        }                    }                case 2:                default:                    break;                case 3:                    if (var2[0].getName().equals("[Ljava.lang.Class;") && var2[1].getName().equals("[Ljava.lang.Object;") && var2[2].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {                        return 4;                    }                }            }            break;        case 1817099975:            if (var1.equals("setCallback")) {                switch(var2.length) {                case 2:                    if (var2[0].getName().equals("int") && var2[1].getName().equals("net.sf.cglib.proxy.Callback")) {                        return 7;                    }                }            }            break;        case 1905679803:            if (var1.equals("getCallback")) {                switch(var2.length) {                case 1:                    if (var2[0].getName().equals("int")) {                        return 11;                    }                }            }            break;        ...        return -1;    }    public int getIndex(Class[] var1) {        switch(var1.length) {        case 0:            return 0;        default:            return -1;        }    }        // 根据index var1调用代理商对象var2的方法    public Object invoke(int var1, Object var2, Object[] var3) throws InvocationTargetException {        148ae4e var10000 = (148ae4e)var2;        int var10001 = var1;        try {            switch(var10001) {            ...            case 4:                return var10000.newInstance((Class[])var3[0], (Object[])var3[1], (Callback[])var3[2]);            case 5:                return var10000.newInstance((Callback[])var3[0]);            case 6:                return var10000.newInstance((Callback)var3[0]);            case 7:                var10000.setCallback(((Number)var3[0]).intValue(), (Callback)var3[1]);                return null;            case 8:                // 调用代理商对象的doSomething方法                var10000.doSomething();                return null;            case 9:                // 调用代理商对象的doSomethingAgain方法                var10000.doSomethingAgain();                return null;            case 10:                var10000.setCallbacks((Callback[])var3[0]);                return null;            case 11:                return var10000.getCallback(((Number)var3[0]).intValue());            case 12:                return var10000.getCallbacks();            case 13:                148ae4e.CGLIB$SET_STATIC_CALLBACKS((Callback[])var3[0]);                return null;            case 14:                148ae4e.CGLIB$SET_THREAD_CALLBACKS((Callback[])var3[0]);                return null;            case 15:                var10000.CGLIB$doSomethingAgain$1();                return null;            ...            case 20:                return 148ae4e.CGLIB$findMethodProxy((Signature)var3[0]);            case 21:                148ae4e.CGLIB$STATICHOOK1();                return null;            case 22:                var10000.CGLIB$doSomething$0();                return null;            }        } catch (Throwable var4) {            throw new InvocationTargetException(var4);        }        throw new IllegalArgumentException("Cannot find matching method/constructor");    }    public Object newInstance(int var1, Object[] var2) throws InvocationTargetException {        148ae4e var10000 = new 148ae4e;        148ae4e var10001 = var10000;        int var10002 = var1;        try {            switch(var10002) {            case 0:                var10001.<init>();                return var10000;            }        } catch (Throwable var3) {            throw new InvocationTargetException(var3);        }        throw new IllegalArgumentException("Cannot find matching method/constructor");    }    public int getMaxIndex() {        return 22;    }}

fastClass机制是为了加快执行速度、减少运行时反射，通过上述代码分析，可以明确method.invoke和methodProxy.invokeSuper的区别

Spring的动态代理商是怎样玩的

Spring Aop及周边框架大量用到动态代理商，在Spring中通过注解使用Aop：

@Configuration@Aspectpublic class AopTest {    @Pointcut("execution(* com.example.demo.controller.*.*(..))")    public void pointCut() {        System.out.println("This is a pointcut");    }    @Before("pointCut()")    public void begin() {        System.out.println("Pointcut begin");    }    @After("pointCut()")    public void after() {        System.out.println("Pointcut end");    }}@Configuration@Aspectpublic class AopAnotherTest {    @Pointcut("execution(* com.example.demo.controller.*.*(..))")    public void pointAnotherCut() {        System.out.println("This is a another pointcut");    }    @Before("pointAnotherCut()")    public void begin() {        System.out.println("Another pointcut begin");    }    @After("pointAnotherCut()")    public void after() {        System.out.println("Another pointcut end");    }}@RestControllerpublic class AopController implements Datasource {    @RequestMapping(path = "/aop/test", method = RequestMethod.GET)    public ResponseEntity testAop() {        System.out.println("testAop");        return ResponseEntity.ok().body(null);    }}

除了上述代码外，还需要在启动类增加注解@EnableAspectJAutoProxy
之所以设置两个切面，主要是想说明Spring是对所有切面进行统一解决，而不是每个单独解决一次，执行结果如下：

Another pointcut beginPointcut begintestAopPointcut endAnother pointcut end  

Spring在bean初始化之前通过beanPostProcessor机制创立代理商类，具体流程见图：

image

其中getAdvisors部分会将该bean所有方法相关的advisor组织到一起解决，如下:

// 将class的所有method过一遍for (Method method : getAdvisorMethods(aspectClass)) {    // 获取method对应的Advisor    Advisor advisor = getAdvisor(method, lazySingletonAspectInstanceFactory, advisors.size(), aspectName);    if (advisor != null) {        advisors.add(advisor);    }}

JDK动态代理商部分会获取到该bean类的所有接口，而后附加少量SpringProxy的特有接口，调用Proxy生成动态代理商类，重点看下Cglib解决，和之前的讲述略微有点不同

Cglib getProxy方法：

public Object getProxy(@Nullable ClassLoader classLoader) {    ...    // 获取被代理商类    Class<?> rootClass = this.advised.getTargetClass();    Assert.state(rootClass != null, "Target class must be available for creating a CGLIB proxy");        Class<?> proxySuperClass = rootClass;    // 假如该类已经是cglib代理商类    if (ClassUtils.isCglibProxyClass(rootClass)) {        // 获取原被代理商类，将要生成的动态代理商类为该类的子类        proxySuperClass = rootClass.getSuperclass();        Class<?>[] additionalInterfaces = rootClass.getInterfaces();        for (Class<?> additionalInterface : additionalInterfaces) {            this.advised.addInterface(additionalInterface);        }    }    ...        // Configure CGLIB Enhancer...    Enhancer enhancer = createEnhancer();    if (classLoader != null) {        enhancer.setClassLoader(classLoader);        if (classLoader instanceof SmartClassLoader &&                ((SmartClassLoader) classLoader).isClassReloadable(proxySuperClass)) {            enhancer.setUseCache(false);        }    }    // 生成的动态代理商类为原被代理商类的子类    enhancer.setSuperclass(proxySuperClass);    // 获取被代理商类所有接口，附加SpringProxy特有接口    enhancer.setInterfaces(AopProxyUtils.completeProxiedInterfaces(this.advised));    enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);    enhancer.setStrategy(new ClassLoaderAwareUndeclaredThrowableStrategy(classLoader));        // 重点关注callback逻辑    Callback[] callbacks = getCallbacks(rootClass);    Class<?>[] types = new Class<?>[callbacks.length];    for (int x = 0; x < types.length; x++) {        types[x] = callbacks[x].getClass();    }        // callbackFilter的作用是根据条件过滤出调用的callback    enhancer.setCallbackFilter(new ProxyCallbackFilter(        this.advised.getConfigurationOnlyCopy(), this.fixedInterceptorMap, this.fixedInterceptorOffset));    enhancer.setCallbackTypes(types);        // Generate the proxy class and create a proxy instance.    return createProxyClassAndInstance(enhancer, callbacks);

重点看下getCallBacks：

private Callback[] getCallbacks(Class<?> rootClass) throws Exception {    // 和EnableAspectJAutoProxy配置有关，能否将proxy暴露到上下文AopContext，默认为false    boolean exposeProxy = this.advised.isExposeProxy();    // 动态代理商配置能否不允许修改，和优化有关，默认为false    boolean isFrozen = this.advised.isFrozen();    // 能否每次都返回同一个代理商对象，也就是代理商对象可以被缓存，跟bean的生命周期有关    boolean isStatic = this.advised.getTargetSource().isStatic();    // Choose an "aop" interceptor (used for AOP calls).    // 这个是重点，aop代理商就走这个interceptor    Callback aopInterceptor = new DynamicAdvisedInterceptor(this.advised);    // Choose a "straight to target" interceptor. (used for calls that are    // unadvised but can return this). May be required to expose the proxy.    Callback targetInterceptor;    if (exposeProxy) {        targetInterceptor = isStatic ?            new StaticUnadvisedExposedInterceptor(this.advised.getTargetSource().getTarget()) :            new DynamicUnadvisedExposedInterceptor(this.advised.getTargetSource());    }    else {        targetInterceptor = isStatic ?            // 一般走这里            new StaticUnadvisedInterceptor(this.advised.getTargetSource().getTarget()) :            new DynamicUnadvisedInterceptor(this.advised.getTargetSource());    }    // Choose a "direct to target" dispatcher (used for    // unadvised calls to static targets that cannot return this).    Callback targetDispatcher = isStatic ?        new StaticDispatcher(this.advised.getTargetSource().getTarget()) : new SerializableNoOp();    Callback[] mainCallbacks = new Callback[] {        aopInterceptor,  // for normal advice        targetInterceptor,  // invoke target without considering advice, if optimized        new SerializableNoOp(),  // no override for methods mapped to this        targetDispatcher, this.advisedDispatcher,        new EqualsInterceptor(this.advised),        new HashCodeInterceptor(this.advised)    };    ...}

看下Aop相关的DynamicAdvisedInterceptor的intercept方法：

public Object intercept(Object proxy, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {    Object oldProxy = null;    boolean setProxyContext = false;    Object target = null;    TargetSource targetSource = this.advised.getTargetSource();    try {          ...          target = targetSource.getTarget();          Class<?> targetClass = (target != null ? target.getClass() : null);          // 重点：将所有的MethodInterceptor串成一个链          List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);          Object retVal;        ...        // proxy为动态代理商后的bean        // target为原bean        // proceed方法为解决之前提到的chain上所有methodInterceptor        // 最后一个methodinterceptor调用methodProxy的invoke方法        // methodProxy.invoke(this.target, this.arguments);        retVal = new CglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();                retVal = processReturnType(proxy, target, method, retVal);        return retVal;    }    finally {        if (target != null && !targetSource.isStatic()) {            targetSource.releaseTarget(target);        }        if (setProxyContext) {            // Restore old proxy.            AopContext.setCurrentProxy(oldProxy);        }    }}

所有的methodInterceptor组成chain，依次调用，最后一个methodinterceptor调用methodProxy的invoke方法：

methodProxy.invoke(this.target, this.arguments);

这里的target为原始bean，不会陷入死循环，和cglib的分析呼应。

看到这的都是爱钻研的好同学

68号小喇叭