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java 代理模式 从静态代理到动态代理

java 代理模式 从静态代理到动态代理

作者: 饱饱想要的灵感 | 来源:发表于2022-09-06 21:18 被阅读0次

如果想在访问某个类时, 做一些其它的控制, 可以增加一个中间类, 此中间类即为代理对象,

静态代理与动态代理的概念

  1. 代理类在编译时就被确定的，称之为静态代理。
    静态代理有两个弊端:
    一是有多少类需要代理, 就要手写多少代理类;
    二是当被代理类的方法出现变动时, 需要同步修改代理类.
  2. 代理类在运行时动态生成的，称之为动态代理。
    动态代理的基本原理是程序运行时, 动态生成字节码载入JVM;
    常见的动态代理有JDK动态代理和Cglib动态代理2种.

静态代理

接口类

public interface Service {
    void execute();
}

实现类

public class RealServiceImpl implements Service{
    @Override
    public void execute() {
        try {
            Thread.sleep(2000);
            System.out.println("吾爱孟夫子，风流天下闻。\n" +
                    "红颜弃轩冕，白首卧松云。\n" +
                    "醉月频中圣，迷花不事君。\n" +
                    "高山安可仰，徒此揖清芬。");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

静态代理类

public class StaticProxyServiceImpl implements Service {
    private Service service;
    public StaticProxyServiceImpl(Service service) {
        this.service = service;
    }

    @Override
    public void execute() {
        long startTime = System.currentTimeMillis();
        service.execute();
        System.out.println("通过静态代理执行,耗时:" + DateUtil.totalSpend(startTime, System.currentTimeMillis()));    }
}

JDK动态代理

实现原理:

  1. 被代理对象必须是某个接口的实现类, 如以上静态代理的RealServiceImpl
  2. 新增一个创建器类实现InvocationHandler接口, 注入被代理的对象
  3. 在覆写方法invoke()中通过反射method.invoke()来调用
  4. 通过Proxy.newProxyInstance()创建代理对象
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class JavaDynamicProxyImpl implements InvocationHandler {

    private Object targetObject;

    private JavaDynamicProxyImpl(Object targetObject) {
        this.targetObject = targetObject;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        long startTime = System.currentTimeMillis();
        Object result = method.invoke(targetObject, args);
        System.out.println("通过Java动态代理执行,耗时：" + DateUtil.totalSpend(startTime, System.currentTimeMillis()));
        return result;
    }

    /**
    * 创建代理对象, 注意T是接口
    */
    public static <T> T newProxyInstance(T t) {
        long startTime = System.currentTimeMillis();
        JavaDynamicProxyImpl dynamicProxyService = new JavaDynamicProxyImpl(t);
        T proxyInstance = (T) Proxy.newProxyInstance(
                dynamicProxyService.getClass().getClassLoader(),
                t.getClass().getInterfaces(),
                dynamicProxyService);
        System.out.printf("创建Java动态代理对象,耗时:%s\n", DateUtil.totalSpend(startTime, System.currentTimeMillis()));
        return proxyInstance;
    }
}

可通过如下代码查看JDK动态代理生成的字节码

    @Test
    public void lookJavaDynamicProxyClassFile() throws IOException {
        byte[] bytes = ProxyGenerator.generateProxyClass("JavaDynamicProxyImpl", new Class[] { Service.class });
        FileOutputStream outputStream = new FileOutputStream(new File("D:/repo/boot/src/test/java/proxy/proxy/JavaDynamicProxyImpl.class"));
        outputStream.write(bytes);
        outputStream.flush();
        outputStream.close();
    }

Cglib动态代理

实现原理:

  1. Cglib动态代理一般见于Spring的AOP, 当一个类未实现某个接口时, Spring将采用Cglib动态代理, 否则采用JDK动态代理
  2. 新增一个创建器类实现MethodInterceptor接口, 在覆写方法中通过子类代理方法methodProxy.invokeSuper()来调用
  3. 而创建代理对象, 是通过字节码增强器, 动态创建一个被代理对象的子类, 由子类来调用, 也因此, 声明了final的方法无法进行AOP切面, 这点在实际开发中需要极其注意. (若存在final方法, Spring启动时会有类似于public final * cannot get proxied via CGLIB的日志)
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;

public class CglibProxyImpl implements MethodInterceptor {

    private CglibProxyImpl(){}

    @Override
    public Object intercept(Object proxyObj, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        long startTime = System.currentTimeMillis();
        Object result = methodProxy.invokeSuper(proxyObj, args);
        System.out.println("通过Cglib执行,耗时：" + DateUtil.totalSpend(startTime, System.currentTimeMillis()));
        return result;
    }

    /**
    * 创建代理对象
    */
    public static <T> T newProxyInstance(Class<T> targetInstanceClazz) {
        long startTime = System.currentTimeMillis();
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(targetInstanceClazz);
        enhancer.setCallback(new CglibProxyImpl());
        T t = (T) enhancer.create();
        System.out.println("创建Cglib动态代理,耗时：" + DateUtil.totalSpend(startTime, System.currentTimeMillis()));
        return t;
    }
}

可通过如下代码查看Cglib生成的子类

    @Test
    public void lookCglibProxyClassFile() {
        System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "D:/repo/boot/src/test/java/proxy");
        CglibProxyImpl.newProxyInstance(RealServiceImpl.class);
        CglibProxyImpl.newProxyInstance(CatServiceImpl.class);
    }

两种动态代理的对比

JDK动态代理创建代理对象比Cglib更快, 而调用时相差不大

附: 测试代码及两种动态代理生成的字节码

测试代码:

    @Test
    public void staticProxyTest() {
        Service realService = new RealServiceImpl();
        Service proxy = new StaticProxyServiceImpl(realService);
        proxy.execute();
    }


    @Test
    public void javaDynamicProxyTest() {
        Service realService = new RealServiceImpl();
        JavaDynamicProxyImpl.newProxyInstance(realService ).execute();
    }


    @Test
    public void cglibProxyTest() {
        CglibProxyImpl.newProxyInstance(RealServiceImpl.class).execute();
    }

JDK动态代理生成的字节码:

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

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import proxy.Service;

public final class ProxyServiceImpl extends Proxy implements Service {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public ProxyServiceImpl(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 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 void execute() throws  {
        try {
            super.h.invoke(this, m3, (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);
        }
    }

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

Cglib动态代理生成的字节码:

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

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 RealServiceImpl$$EnhancerByCGLIB$$8572e518 extends RealServiceImpl 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$execute$0$Method;
    private static final MethodProxy CGLIB$execute$0$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.RealServiceImpl$$EnhancerByCGLIB$$8572e518");
        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$4");
        CGLIB$execute$0$Method = ReflectUtils.findMethods(new String[]{"execute", "()V"}, (var1 = Class.forName("proxy.RealServiceImpl")).getDeclaredMethods())[0];
        CGLIB$execute$0$Proxy = MethodProxy.create(var1, var0, "()V", "execute", "CGLIB$execute$0");
    }

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

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

    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 539325408:
            if (var10000.equals("execute()V")) {
                return CGLIB$execute$0$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 RealServiceImpl$$EnhancerByCGLIB$$8572e518() {
        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) {
        RealServiceImpl$$EnhancerByCGLIB$$8572e518 var1 = (RealServiceImpl$$EnhancerByCGLIB$$8572e518)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);
        RealServiceImpl$$EnhancerByCGLIB$$8572e518 var10000 = new RealServiceImpl$$EnhancerByCGLIB$$8572e518();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Callback var1) {
        CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
        RealServiceImpl$$EnhancerByCGLIB$$8572e518 var10000 = new RealServiceImpl$$EnhancerByCGLIB$$8572e518();
        CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
        return var10000;
    }

    public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
        CGLIB$SET_THREAD_CALLBACKS(var3);
        RealServiceImpl$$EnhancerByCGLIB$$8572e518 var10000 = new RealServiceImpl$$EnhancerByCGLIB$$8572e518;
        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();
    }
}

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