前提

前一篇文章介绍了CGLIB中常用的API,实际上使用了EnhancerMethodInterceptor之后会生成代理子类,这篇文章就是分析一下CGLIB动态代理的原理。

CGLIB动态代理原理分析

我们经常说CGLIB的动态代理的底层通过被代理类生成代理子类实现的,那么下面我们就分析一下生成的子类到底是什么样的。开启CGLIB的debug模式,输出它生成的类到指定的目录:

public class DebuggingCglibDemo {

	private static final String METHOD_NAME = "sayHello";

	public static void main(String[] args) throws Exception {
		String location = DebuggingCglibDemo.class.getResource("").getPath() + "debugging/";
		System.out.println("location -> " + location);
		System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, location);
		Enhancer enhancer = new Enhancer();
		enhancer.setSuperclass(SampleClass.class);
		enhancer.setCallback(new MethodInterceptor() {
			@Override
			public Object intercept(Object obj, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
				Object result;
				if (METHOD_NAME.equals(method.getName())) {
					System.out.println("Before invoking sayHello...");
					result = methodProxy.invokeSuper(obj, objects);
					System.out.println("After invoking sayHello...");
				} else {
					result = methodProxy.invokeSuper(obj, objects);
				}
				return result;
			}
		});
		SampleClass sampleClass = (SampleClass) enhancer.create();
		System.out.println(sampleClass.sayHello("throwable"));
	}
}

输出结果:

location -> /D:/Projects/cglib-seed/target/classes/club/throwable/cglib/debugging/
CGLIB debugging enabled, writing to '/D:/Projects/cglib-seed/target/classes/club/throwable/cglib/debugging/'
Before invoking sayHello...
After invoking sayHello...
throwable say hello!

这个时候,看下target下面生成的类如下:

c-d-p-1

一共有五个类:

../net.sf.cglib包下:

MethodWrapper$MethodWrapperKey$$KeyFactoryByCGLIB$$d45e49f7.class
Enhancer$EnhancerKey$$KeyFactoryByCGLIB$$7fb24d72.class

这两个类主要很缓存的Key相关,这里不做详细展开。

用户自定义包../club/throwable/cglib包下:

  • SampleClass$$EnhancerByCGLIB$$53c7afed$$FastClassByCGLIB$$da5c8621.class
  • SampleClass$$EnhancerByCGLIB$$53c7afed.class
  • SampleClass$$FastClassByCGLIB$$cf1a549b.class

这三个就是实际使用到的子类,其中有一个是被代理类的直接子类SampleClass$$EnhancerByCGLIB$$53c7afed,其他的两个是FastClass

接着我们先看一下SampleClass$$EnhancerByCGLIB$$53c7afed这个类的源码:

与Java原生代理类似,仍然以静态变量保存了指向代理方法的引用
    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;
	//每个函数有两个反射方法,一个是通过原生反射获得的,另外一个是通过Cglib构建的。
    private static final Method CGLIB$sayHello$0$Method;
    private static final MethodProxy CGLIB$sayHello$0$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;

    //这里通过静态代码块初始化上面用到的静态变量,主要使用到反射
    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("club.throwable.cglib.SampleClass$$EnhancerByCGLIB$$53c7afed");
        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$4");
        CGLIB$sayHello$0$Method = ReflectUtils.findMethods(new String[]{"sayHello", "(Ljava/lang/String;)Ljava/lang/String;"}, (var1 = Class.forName("club.throwable.cglib.SampleClass")).getDeclaredMethods())[0];
        CGLIB$sayHello$0$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Ljava/lang/String;", "sayHello", "CGLIB$sayHello$0");
    }

    //这个方法就是直接调用原来的被代理类(父类)的方法
    final String CGLIB$sayHello$0(String var1) {
        return super.sayHello(var1);
    }
    //这个方法就是通过方法代理进行回调,里面用到了Callback实例
    public final String sayHello(String var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        return var10000 != null ? (String)var10000.intercept(this, CGLIB$sayHello$0$Method, new Object[]{var1}, CGLIB$sayHello$0$Proxy) : super.sayHello(var1);
    }

    final boolean CGLIB$equals$1(Object var1) {
        return super.equals(var1);
    }

    public final boolean equals(Object var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == 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$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == 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$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == 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$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == 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$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -1816210712:
            if (var10000.equals("sayHello(Ljava/lang/String;)Ljava/lang/String;")) {
                return CGLIB$sayHello$0$Proxy;
            }
            break;
        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 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 SampleClass$$EnhancerByCGLIB$$53c7afed() {
        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) {
        SampleClass$$EnhancerByCGLIB$$53c7afed var1 = (SampleClass$$EnhancerByCGLIB$$53c7afed)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];
        }

    }

    public Object newInstance(Callback[] var1) {
        CGLIB$SET_THREAD_CALLBACKS(var1);
        SampleClass$$EnhancerByCGLIB$$53c7afed var10000 = new SampleClass$$EnhancerByCGLIB$$53c7afed();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        SampleClass$$EnhancerByCGLIB$$53c7afed var10000 = new SampleClass$$EnhancerByCGLIB$$53c7afed();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        SampleClass$$EnhancerByCGLIB$$53c7afed var10000 = new SampleClass$$EnhancerByCGLIB$$53c7afed;
        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();
    }
}

这个类十分长,因为里面有很多的变量,它们都通过了静态代码块使用反射初始化。类的代码比JDK动态代理的子类多,因此生成效率会比较低。相关比较重要的注释已经写在类中,我们最主要关注两点:

  • 第一点:
private static final Method CGLIB$sayHello$0$Method;
private static final MethodProxy CGLIB$sayHello$0$Proxy;

这两个静态变量都是指向sayHello这个方法,CGLIB$sayHello$0$Method直接指向父类方法,CGLIB$sayHello$0$Proxy是CGLIB生成的方法代理。

  • 第二点:
    //这个方法就是直接调用原来的被代理类(父类)的方法
    final String CGLIB$sayHello$0(String var1) {
        return super.sayHello(var1);
    }
    //这个方法就是通过方法代理进行回调,里面用到了Callback实例
    public final String sayHello(String var1) {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }
        //如果找不到Callback会直接调用父类的原方法
        return var10000 != null ? (String)var10000.intercept(this, CGLIB$sayHello$0$Method, new Object[]{var1}, CGLIB$sayHello$0$Proxy) : super.sayHello(var1);
    }

也就是如果想要启用CGLIB的回调,我们主观上应该是这样操作的:

SampleClass$$EnhancerByCGLIB$$53c7afed sample = new SampleClass$$EnhancerByCGLIB$$53c7afed();
sample.sayHello("doge");

但是由于这个代理类是动态生成的,只能通过反射调用。

那么,剩下的两个FastClass的作用是什么?我们先看一下MethodProxyinvoke()invokeSuper()方法:

     //初始化FastClass中的index索引
     private void init() {
        if (this.fastClassInfo == null) {
            Object var1 = this.initLock;
            synchronized(this.initLock) {
                if (this.fastClassInfo == null) {
                    MethodProxy.CreateInfo ci = this.createInfo;
                    MethodProxy.FastClassInfo fci = new MethodProxy.FastClassInfo();
                    fci.f1 = helper(ci, ci.c1);
                    fci.f2 = helper(ci, ci.c2);
                    fci.i1 = fci.f1.getIndex(this.sig1);
                    fci.i2 = fci.f2.getIndex(this.sig2);
                    this.fastClassInfo = fci;
                    this.createInfo = null;
                }
            }
        }
    }

   public Object invoke(Object obj, Object[] args) throws Throwable {
        try {
            this.init();
            MethodProxy.FastClassInfo fci = this.fastClassInfo;
            return fci.f1.invoke(fci.i1, obj, args);
        } catch (InvocationTargetException var4) {
            throw var4.getTargetException();
        } catch (IllegalArgumentException var5) {
            if (this.fastClassInfo.i1 < 0) {
                throw new IllegalArgumentException("Protected method: " + this.sig1);
            } else {
                throw var5;
            }
        }
    }

    public Object invokeSuper(Object obj, Object[] args) throws Throwable {
        try {
            this.init();
            MethodProxy.FastClassInfo fci = this.fastClassInfo;
            return fci.f2.invoke(fci.i2, obj, args);
        } catch (InvocationTargetException var4) {
            throw var4.getTargetException();
        }
    }

这里,两个方法各自使用了不同的FastClassInfo实例fci.f2fci.f2。其中,SampleClass$$FastClassByCGLIB$$cf1a549b.class是对应于父类,而SampleClass$$EnhancerByCGLIB$$53c7afed$$FastClassByCGLIB$$da5c8621是对应于CGLIB生成的被代理类的子类。下面展开SampleClass$$EnhancerByCGLIB$$53c7afed$$FastClassByCGLIB$$da5c8621的源码:

public class SampleClass$$EnhancerByCGLIB$$53c7afed$$FastClassByCGLIB$$da5c8621 extends FastClass {
    public SampleClass$$EnhancerByCGLIB$$53c7afed$$FastClassByCGLIB$$da5c8621(Class var1) {
        super(var1);
    }

    public int getIndex(Signature var1) {
        String var10000 = var1.toString();
        switch(var10000.hashCode()) {
        case -2055565910:
            if (var10000.equals("CGLIB$SET_THREAD_CALLBACKS([Lnet/sf/cglib/proxy/Callback;)V")) {
                return 10;
            }
            break;
        case -1882565338:
            if (var10000.equals("CGLIB$equals$1(Ljava/lang/Object;)Z")) {
                return 18;
            }
            break;
        case -1816210712:
            if (var10000.equals("sayHello(Ljava/lang/String;)Ljava/lang/String;")) {
                return 7;
            }
            break;
        case -1457535688:
            if (var10000.equals("CGLIB$STATICHOOK1()V")) {
                return 15;
            }
            break;
        case -1411842725:
            if (var10000.equals("CGLIB$hashCode$3()I")) {
                return 19;
            }
            break;
        case -894172689:
            if (var10000.equals("newInstance(Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {
                return 5;
            }
            break;
        case -623122092:
            if (var10000.equals("CGLIB$findMethodProxy(Lnet/sf/cglib/core/Signature;)Lnet/sf/cglib/proxy/MethodProxy;")) {
                return 14;
            }
            break;
        case -508378822:
            if (var10000.equals("clone()Ljava/lang/Object;")) {
                return 3;
            }
            break;
        case -419626537:
            if (var10000.equals("setCallbacks([Lnet/sf/cglib/proxy/Callback;)V")) {
                return 13;
            }
            break;
        case 560567118:
            if (var10000.equals("setCallback(ILnet/sf/cglib/proxy/Callback;)V")) {
                return 8;
            }
            break;
        case 811063227:
            if (var10000.equals("newInstance([Ljava/lang/Class;[Ljava/lang/Object;[Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {
                return 6;
            }
            break;
        case 973717575:
            if (var10000.equals("getCallbacks()[Lnet/sf/cglib/proxy/Callback;")) {
                return 11;
            }
            break;
        case 1221173700:
            if (var10000.equals("newInstance([Lnet/sf/cglib/proxy/Callback;)Ljava/lang/Object;")) {
                return 4;
            }
            break;
        case 1230699260:
            if (var10000.equals("getCallback(I)Lnet/sf/cglib/proxy/Callback;")) {
                return 12;
            }
            break;
        case 1298742135:
            if (var10000.equals("CGLIB$sayHello$0(Ljava/lang/String;)Ljava/lang/String;")) {
                return 16;
            }
            break;
        case 1306468936:
            if (var10000.equals("CGLIB$toString$2()Ljava/lang/String;")) {
                return 20;
            }
            break;
        case 1584330438:
            if (var10000.equals("CGLIB$SET_STATIC_CALLBACKS([Lnet/sf/cglib/proxy/Callback;)V")) {
                return 9;
            }
            break;
        case 1800494055:
            if (var10000.equals("CGLIB$clone$4()Ljava/lang/Object;")) {
                return 17;
            }
            break;
        case 1826985398:
            if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
                return 0;
            }
            break;
        case 1913648695:
            if (var10000.equals("toString()Ljava/lang/String;")) {
                return 1;
            }
            break;
        case 1984935277:
            if (var10000.equals("hashCode()I")) {
                return 2;
            }
        }

        return -1;
    }

    public int getIndex(String var1, Class[] var2) {
        switch(var1.hashCode()) {
        case -2012993625:
            if (var1.equals("sayHello")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("java.lang.String")) {
                        return 7;
                    }
                }
            }
            break;
        case -1983192202:
            if (var1.equals("CGLIB$sayHello$0")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("java.lang.String")) {
                        return 16;
                    }
                }
            }
            break;
        case -1776922004:
            if (var1.equals("toString")) {
                switch(var2.length) {
                case 0:
                    return 1;
                }
            }
            break;
        case -1295482945:
            if (var1.equals("equals")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("java.lang.Object")) {
                        return 0;
                    }
                }
            }
            break;
        case -1053468136:
            if (var1.equals("getCallbacks")) {
                switch(var2.length) {
                case 0:
                    return 11;
                }
            }
            break;
        case -124978609:
            if (var1.equals("CGLIB$equals$1")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("java.lang.Object")) {
                        return 18;
                    }
                }
            }
            break;
        case -60403779:
            if (var1.equals("CGLIB$SET_STATIC_CALLBACKS")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {
                        return 9;
                    }
                }
            }
            break;
        case -29025555:
            if (var1.equals("CGLIB$hashCode$3")) {
                switch(var2.length) {
                case 0:
                    return 19;
                }
            }
            break;
        case 85179481:
            if (var1.equals("CGLIB$SET_THREAD_CALLBACKS")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {
                        return 10;
                    }
                }
            }
            break;
        case 94756189:
            if (var1.equals("clone")) {
                switch(var2.length) {
                case 0:
                    return 3;
                }
            }
            break;
        case 147696667:
            if (var1.equals("hashCode")) {
                switch(var2.length) {
                case 0:
                    return 2;
                }
            }
            break;
        case 161998109:
            if (var1.equals("CGLIB$STATICHOOK1")) {
                switch(var2.length) {
                case 0:
                    return 15;
                }
            }
            break;
        case 495524492:
            if (var1.equals("setCallbacks")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {
                        return 13;
                    }
                }
            }
            break;
        case 1154623345:
            if (var1.equals("CGLIB$findMethodProxy")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("net.sf.cglib.core.Signature")) {
                        return 14;
                    }
                }
            }
            break;
        case 1543336189:
            if (var1.equals("CGLIB$toString$2")) {
                switch(var2.length) {
                case 0:
                    return 20;
                }
            }
            break;
        case 1811874389:
            if (var1.equals("newInstance")) {
                switch(var2.length) {
                case 1:
                    String var10001 = var2[0].getName();
                    switch(var10001.hashCode()) {
                    case -845341380:
                        if (var10001.equals("net.sf.cglib.proxy.Callback")) {
                            return 5;
                        }
                        break;
                    case 1730110032:
                        if (var10001.equals("[Lnet.sf.cglib.proxy.Callback;")) {
                            return 4;
                        }
                    }
                case 2:
                default:
                    break;
                case 3:
                    if (var2[0].getName().equals("[Ljava.lang.Class;") && var2[1].getName().equals("[Ljava.lang.Object;") && var2[2].getName().equals("[Lnet.sf.cglib.proxy.Callback;")) {
                        return 6;
                    }
                }
            }
            break;
        case 1817099975:
            if (var1.equals("setCallback")) {
                switch(var2.length) {
                case 2:
                    if (var2[0].getName().equals("int") && var2[1].getName().equals("net.sf.cglib.proxy.Callback")) {
                        return 8;
                    }
                }
            }
            break;
        case 1905679803:
            if (var1.equals("getCallback")) {
                switch(var2.length) {
                case 1:
                    if (var2[0].getName().equals("int")) {
                        return 12;
                    }
                }
            }
            break;
        case 1951977610:
            if (var1.equals("CGLIB$clone$4")) {
                switch(var2.length) {
                case 0:
                    return 17;
                }
            }
        }

        return -1;
    }

    public int getIndex(Class[] var1) {
        switch(var1.length) {
        case 0:
            return 0;
        default:
            return -1;
        }
    }

    public Object invoke(int var1, Object var2, Object[] var3) throws InvocationTargetException {
        53c7afed var10000 = (53c7afed)var2;
        int var10001 = var1;

        try {
            switch(var10001) {
            case 0:
                return new Boolean(var10000.equals(var3[0]));
            case 1:
                return var10000.toString();
            case 2:
                return new Integer(var10000.hashCode());
            case 3:
                return var10000.clone();
            case 4:
                return var10000.newInstance((Callback[])var3[0]);
            case 5:
                return var10000.newInstance((Callback)var3[0]);
            case 6:
                return var10000.newInstance((Class[])var3[0], (Object[])var3[1], (Callback[])var3[2]);
            case 7:
                return var10000.sayHello((String)var3[0]);
            case 8:
                var10000.setCallback(((Number)var3[0]).intValue(), (Callback)var3[1]);
                return null;
            case 9:
                53c7afed.CGLIB$SET_STATIC_CALLBACKS((Callback[])var3[0]);
                return null;
            case 10:
                53c7afed.CGLIB$SET_THREAD_CALLBACKS((Callback[])var3[0]);
                return null;
            case 11:
                return var10000.getCallbacks();
            case 12:
                return var10000.getCallback(((Number)var3[0]).intValue());
            case 13:
                var10000.setCallbacks((Callback[])var3[0]);
                return null;
            case 14:
                return 53c7afed.CGLIB$findMethodProxy((Signature)var3[0]);
            case 15:
                53c7afed.CGLIB$STATICHOOK1();
                return null;
            case 16:
                return var10000.CGLIB$sayHello$0((String)var3[0]);
            case 17:
                return var10000.CGLIB$clone$4();
            case 18:
                return new Boolean(var10000.CGLIB$equals$1(var3[0]));
            case 19:
                return new Integer(var10000.CGLIB$hashCode$3());
            case 20:
                return var10000.CGLIB$toString$2();
            }
        } catch (Throwable var4) {
            throw new InvocationTargetException(var4);
        }

        throw new IllegalArgumentException("Cannot find matching method/constructor");
    }

    public Object newInstance(int var1, Object[] var2) throws InvocationTargetException {
        53c7afed var10000 = new 53c7afed;
        53c7afed 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 20;
    }
}

这个类更加长,但是其实大部分都是switch-case的代码块,它的功能就是为方法的调用添加基于整型数字的索引,主要目的是为了减少反射调用的时间,将反射调用转化为直接调用。简单来说,invokeSuper的流程就是这样的

  • 通过MethodProxy的init方法,用当前方法的Signature(签名)构建两个FastClass实例(当然,这里会做缓存)和当前方法对应的index,存放在FastClassInfo实例中。
  • 通过FastClassInfo中的FastClass实例和index,在FastClass中找到对应的方法(在switch-case块中基于整数索引index进行查找)直接调用。

直观来看,CGLIB在类生成期间的操作会相对耗时,而且生成的类数目比较多,会占据大量永久代或者元空间的内存。子类一旦生成,后面的方法调用就会变成搜索方法索引和直接调用,这样的操作在特定的条件下效率会比JDK的反射高。这里特定的场景是指CGLIB子类中的switch-case块不大并且当前调用的方法的index在switch-case块的前部而不是中后部(简单来说就是子类中的方法要尽量少从而提高switch-case中的搜寻效率)。详细可以参考这篇性能对比的文章:cglib和jdk动态代理调用性能测

小结

CGLIB提供了许多基于代码生成的高级功能的API,可以在通过上面的例子熟悉它的使用,并且在合适的场景用于实战中。可能最常用到的是基于Enhancer的动态代理,这里总结一下CGLIB和JDK动态代理的区别(老生常谈):

  • JDK动态代理只能够对接口进行代理,不能对普通的类进行代理(因为所有生成的代理类的父类为Proxy,Java类继承机制不允许多重继承);CGLIB能够代理普通类,但是该普通类必须能够被继承(不能用final修饰符)。
  • JDK动态代理使用Java原生的反射API进行操作,在生成类上比较高效;CGLIB使用ASM框架直接对字节码进行修改,使用了FastClass的特性,在某些情况下类的方法执行会比较高效。

(本文完 e-a-20181216 c-1-d)