JDK動態代理與CGLIB動態代理

JDK動態代理和CGLIB動態代理是SpringAOP非常重要的兩個概念，SpringAOP是通過生成目標對象的代理類來實現對目標對象的增強，在說JDK的動態代理之前我們先來回顧一下靜態代理：

一、靜態代理：

首先定義一個業務接口

public interface ITestService {
    void sayHello();
    String getMsg();
}

然後我們編寫一個簡單的實現類：

public class TestServiceImpl implements ITestService{
    @Override
    public void sayHello() {
        System.out.println("TestServiceImpl sayHello");
    }
    @Override
    public String getMsg() {
        return "TestServiceImpl Msg";
    }
}

然後我們再編寫一個代理類用來代理TestServiceImpl：

public class TestServiceProxy implements ITestService {
    private ITestService target;

    public TestServiceProxy(ITestService testService) {
        this.target = testService;
    }

    @Override
    public void sayHello() {
        System.out.println("sayHello invoke before");
        this.target.sayHello();
        System.out.println("sayHello invoke after");
    }

    @Override
    public String getMsg() {
        System.out.println("getMsg invoke before");
        String result = this.target.getMsg();
        System.out.println("getMsg invoke after");
        return result;
    }
}

最後我們編寫一個場景類來模擬使用場景：

public class Client {
    public static void main(String[] args) {
        ITestService testService = new TestServiceProxy(new TestServiceImpl());
        testService.sayHello();
        String msg = testService.getMsg();
        System.out.println(msg);
    }
}

最後輸出：

結果很簡單，我們通過TestServiceProxy對象實現了對TestServiceImpl的代理，並且這個代理對場景類Clinet是隱藏的，這個就是代理模式。

我們回頭看一下這個靜態代理的實現方式缺點，我們爲了實現對ITestService的實現類的代理，寫了一個代理類TestServiceProxy，這個代理類只能代理ITestService的子類，如果需要代理其他的對象，哪怕代理邏輯是一樣的，也需要重新編寫一個代理類，這樣勢必會導致類的數量大量增加，最終導致項目十分臃腫，JDK1.3中加入的代理模式就解決了這個問題，讓代理類可以代理多個對象，不需要編寫重複的代理邏輯。

二、JDK動態代理

JDK動態代理的核心是InvocationHandler接口，首先我們編寫一個代理類，注意這個代理類的名字是MyProxy，說明它不再與任何具體的接口建立依賴關係。

public class MyProxy implements InvocationHandler {
    private Object target;
    public MyProxy(Object target) {
        this.target = target;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("invoke before");
        Object result = method.invoke(target);
        System.out.println("invoke after");
        return result;
    }
}

接下來通過Proxy.newProxyInstance來生成一個代理對象，此時我們才需要傳入被代理的接口，把與被代理對象建立依賴關係的步驟放到了場景類中。

public class Client {
    public static void main(String[] args) {
        // 將Proxy.newProxyInstance生成的代理對象輸出到com\sun\proxy目錄
        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true);
        MyProxy proxy = new MyProxy(new TestServiceImpl());
        ITestService service = (ITestService) Proxy.newProxyInstance(Client.class.getClassLoader(),
            new Class[]{ITestService.class}, proxy);
        service.sayHello();
        String result = service.getMsg();
        System.out.println(result);
    }
}

輸出結果還是一樣，JDK動態代理其實就是Proxy.newProxyInstance方法幫我們動態生成了一個代理對象，不需要我們手動去編寫了，反編譯查看一下生成的動態代理對象：

public final class $Proxy0 extends Proxy implements ITestService {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;
    private static Method m4;

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

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final void sayHello() 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  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final String getMsg() throws  {
        try {
            return (String)super.h.invoke(this, m4, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("proxy.ITestService").getMethod("sayHello");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
            m4 = Class.forName("proxy.ITestService").getMethod("getMsg");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

可以看到生成的$Proxy0通過繼承Proxy接口來持有InvocationHandler，並且實現了傳入的接口，實際調用method的時候其實是調用的InvocationHandler的invoker方法。通過這種方式實現了代理。並且$Proxy0不僅僅代理了getMsg和sayHello方法，還代理了toString，hasCode，equals等默認方法。

可以看到JDK動態代理的優點，MyProxy中實現的代理邏輯可以應用在任何想要代理的業務對象上，JDK的動態代理也是SpringAOP中默認的代理方式。

但是JDK動態代理是通過繼承Proxy對象，並實現目標對象的父接口的方式來完成代理的，這種方式也有很大的侷限性，如果一個類沒有實現接口，那麼就不能使用JDK動態代理了，就需要用到CGLIB動態代理了。

三、CGLIB動態代理

CGLIB全稱是Code Generation Library，是一個高性能的code生成工具，能夠在程序運行期間動態的擴展JAVA類與實現JAVA接口。

我們來看實現方式，首先編寫一個業務對象，注意這個對象不再實現任何接口，並且將getMsg方法設置爲final類型

public class TestService {
    public void sayHello() {
        System.out.println("TestService sayHello");
    }
    public final String getMsg() {
        return "TestService Msg";
    }
}

CGLIB動態代理的核心是MethodInterceptor接口，我們需要自己編寫一個類去實現MethodInterceptor，這個和InvocationHandler相同：

public class MyMethodInterceptor implements MethodInterceptor {
    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println("前置通知");
        Object result = methodProxy.invokeSuper(o, objects);
        System.out.println("後置通知");
        return result;
    }
}

編寫場景類，使用CGLIB生成代理對象：

public class Client {
    public static void main(String[] args) {
        // 將CGLIB生成的class對象存入磁盤
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, ".\\");

        // 創建Enhancer對象，用來生成代理類
        Enhancer enhancer = new Enhancer();
        // 設置被代理對象
        enhancer.setSuperclass(TestService.class);
        // 設置回調接口，就是的代理邏輯
        enhancer.setCallback(new MyMethodInterceptor());
        // 生成代理對象
        TestService testService= (TestService)enhancer.create();

        // 通過代理對象調用目標方法
        testService.sayHello();
    }
}

結果如下：

生成的class類有三個，另外兩個是爲了生成代理對象服務的：

反編譯出來看看：

package 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 TestService$$EnhancerByCGLIB$$6902e37c extends TestService 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$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;

    static void CGLIB$STATICHOOK1() {
        CGLIB$THREAD_CALLBACKS = new ThreadLocal();
        CGLIB$emptyArgs = new Object[0];
        Class var0 = Class.forName("proxy.TestService$$EnhancerByCGLIB$$6902e37c");
        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", "()V"}, (var1 = Class.forName("proxy.TestService")).getDeclaredMethods())[0];
        CGLIB$sayHello$0$Proxy = MethodProxy.create(var1, var0, "()V", "sayHello", "CGLIB$sayHello$0");
    }

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

    public final void sayHello() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy);
        } else {
            super.sayHello();
        }
    }

    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$findMethodProxy(Signature var0) {
        String var10000 = var0.toString();
        switch(var10000.hashCode()) {
        case -508378822:
            if (var10000.equals("clone()Ljava/lang/Object;")) {
                return CGLIB$clone$4$Proxy;
            }
            break;
        case 1535311470:
            if (var10000.equals("sayHello()V")) {
                return CGLIB$sayHello$0$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 TestService$$EnhancerByCGLIB$$6902e37c() {
        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) {
        TestService$$EnhancerByCGLIB$$6902e37c var1 = (TestService$$EnhancerByCGLIB$$6902e37c)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);
        TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        TestService$$EnhancerByCGLIB$$6902e37c var10000 = new TestService$$EnhancerByCGLIB$$6902e37c;
        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();
    }
}

生成的Class對象是TestService的子類，其中的核心是sayHello方法：

public final void sayHello() {
        MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
        if (this.CGLIB$CALLBACK_0 == null) {
            CGLIB$BIND_CALLBACKS(this);
            var10000 = this.CGLIB$CALLBACK_0;
        }

        if (var10000 != null) {
            var10000.intercept(this, CGLIB$sayHello$0$Method, CGLIB$emptyArgs, CGLIB$sayHello$0$Proxy);
        } else {
            super.sayHello();
        }
    }

可以看到是調用sayHello方法其實是通過MethodInterceptor的intercept方法來調用的，也就實現了代理邏輯。

以上就是JDK動態代理和CGLIB的動態代理，在SpringAOP中，默認是使用JDK動態代理，當一個類沒有父接口時，會改用CBLIB動態代理。

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