[Java知识库]18-深入理解代理模式，jdk代理模式，cglib代理模式

1. 目的

代理模式是一种结构型设计模式， 让你能够提供对象的替代品或其占位符。 代理控制着对于原对象的访问， 并允许在将请求提交给对象前后进行一些处理。

2. 类图

3. 应用场景

• 延迟初始化
• 访问控制
• 记录日志
• 事务处理
• spring的aop

4. 优缺点

5.静态代理

/**
 * Bird类实现接口Flyable，鸟能飞 。
 * <p>问题1：我想统计一下fly()运行多久,简单的方法是修改源码</p>
 * <p>问题2：如果不能修改源码呢，又怎么办。办法是继承。</p>
 * <p>问题3：如果我再想打印日志，怎么办，再来一个类. 虽然能解决问题，但是如果我想做权限拦截，又要再生成一个类，如果
 * 我想既实现日志打印，又想统计时间，又要再生成一个类，这样类越来越多，维护和扩展及其糟糕</p>
 * <p>问题3的解决办法是代理,直接持有Bird实例，这个虽然能解决类爆炸问题，但是没有功能组合问题,解决方法是用接口替换</p>
 * <p>问题4：如果有很多方法需要打印方法前后日志怎么办，办法：动态代理</p>
 *
 * @author tobebetter9527
 * @create 2021/07/31 19:47
 */
public class Main {

  public static void main(String[] args) {
    Bird bird = new Bird();
    BirdTime birdTime = new BirdTime(bird);
    BirdLog birdLog = new BirdLog(birdTime);
    birdLog.fly();
    System.out.println("--------------------");
    BirdLog birdLog1 = new BirdLog(bird);
    BirdTime birdTime1 = new BirdTime(birdLog1);
    birdTime1.fly();
  }
}

class BirdLog implements Flyable {

  private Flyable bird;

  public BirdLog(Flyable bird) {
    this.bird = bird;
  }

  @Override
  public void fly() {
    System.out.println("开始打印日志");
    bird.fly();
    System.out.println("结束打印日志");
  }
}

class BirdTime implements Flyable {

  private Flyable bird;

  public BirdTime(Flyable bird) {
    this.bird = bird;
  }

  @Override
  public void fly() {
    long start = System.currentTimeMillis();
    bird.fly();
    long end = System.currentTimeMillis();
    System.out.println("Run time is " + (end - start));
  }
}

class Bird implements Flyable {

  @Override
  public void fly() {
    System.out.println("I can fly...");
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

interface Flyable {

  void fly();
}

6. JDK动态代理

/**
 * Bird类实现接口Flyable，鸟能飞 。
 * <p>问题1：我想统计一下fly()运行多久,简单的方法是修改源码</p>
 * <p>问题2：如果不能修改源码呢，又怎么办。办法是继承。</p>
 * <p>问题3：如果我再想打印日志，怎么办，再来一个类. 虽然能解决问题，但是如果我想做权限拦截，又要再生成一个类，如果
 * 我想既实现日志打印，又想统计时间，又要再生成一个类，这样类越来越多，维护和扩展及其糟糕</p>
 * <p>问题3的解决办法是代理,直接持有Bird实例，这个虽然能解决类爆炸问题，但是没有功能组合问题,解决方法是用接口替换</p>
 * <p>问题4：如果有很多方法需要打印方法前后日志怎么办，办法：动态代理</p>
 * <p>AOP</p>
 *
 * @author tobebetter9527
 * @create 2021/07/31 19:47
 */
public class Main {

  public static void main(String[] args) {
    Bird bird = new Bird();
    // jdk11,自动生成代理类源码
    System.getProperties().put("jdk.proxy.ProxyGenerator.saveGeneratedFiles", "true");
    Flyable instance = (Flyable) Proxy
        .newProxyInstance(Bird.class.getClassLoader(), new Class[]{Flyable.class}, new BirdLog(bird));
    instance.fly();
  }
}


class BirdLog implements InvocationHandler {

  private Flyable bird;

  public BirdLog(Flyable bird) {
    this.bird = bird;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    before();
    Object invoke = method.invoke(bird, args);
    after();
    return invoke;
  }

  private void before() {
    System.out.println("开始打印日志");
  }

  private void after() {
    System.out.println("结束打印日志");
  }
}

class Bird implements Flyable {

  @Override
  public void fly() {
    System.out.println("I can fly...");
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

interface Flyable {

  void fly();
}

以上代码需要用jdk11会自动生成以下代理类，如果没有jdk11，参考以下文章：

• JDK-查看动态代理生成的源码

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

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

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

  public final boolean equals(Object var1) throws  {
    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 fly() 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);
    }
  }

  static {
    try {
      m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
      m3 = Class.forName("com.freedom.pattern.proxy.proxy.v9.Flyable").getMethod("fly");
      m2 = Class.forName("java.lang.Object").getMethod("toString");
      m0 = Class.forName("java.lang.Object").getMethod("hashCode");
    } catch (NoSuchMethodException var2) {
      throw new NoSuchMethodError(var2.getMessage());
    } catch (ClassNotFoundException var3) {
      throw new NoClassDefFoundError(var3.getMessage());
    }
  }
}

7. cglib代理模式

在maven的pom.xml文件中加入

 <dependency>
    <groupId>cglib</groupId>
    <artifactId>cglib</artifactId>
    <version>3.3.0</version>
  </dependency>

import java.lang.reflect.Method;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

/**
 * cglib无需接口就可以生成代理类
 *
 * @author tobebetter9527
 * @create 2021/08/01 9:40
 */
public class Main {

  public static void main(String[] args) {
    Enhancer enhancer = new Enhancer();
    enhancer.setSuperclass(Bird.class);
    enhancer.setCallback(new BirdLogInterceptor());
    Bird bird = (Bird) enhancer.create();
    bird.fly();
  }

}

class BirdLogInterceptor implements MethodInterceptor {

  @Override
  public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
    System.out.println(obj.getClass().getSuperclass().getName());
    System.out.println("开始打印日志");
    Object o = proxy.invokeSuper(obj, args);
    System.out.println("结束打印日志");
    return o;
  }
}


class Bird {

  public void fly() {
    System.out.println("I can fly ...");
    try {
      Thread.sleep(1000);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

生成源码参考：

• spring查看生成的cglib代理类源码详解

代码如下：

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

package com.freedom.pattern.proxy.cglib;

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

public class Bird$$EnhancerByCGLIB$$3ca31ce7 extends Bird 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$fly$0$Method;
  private static final MethodProxy CGLIB$fly$0$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;

  public Bird$$EnhancerByCGLIB$$3ca31ce7() {
    CGLIB$BIND_CALLBACKS(this);
  }

  static {
    CGLIB$STATICHOOK1();
  }

  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);
    }
  }

  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();
  }

  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();
    }
  }

  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 Object newInstance(Callback var1) {
    CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
    Bird$$EnhancerByCGLIB$$3ca31ce7 var10000 = new Bird$$EnhancerByCGLIB$$3ca31ce7();
    CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
    return var10000;
  }

  public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
    CGLIB$SET_THREAD_CALLBACKS(var3);
    Bird$$EnhancerByCGLIB$$3ca31ce7 var10000 = new Bird$$EnhancerByCGLIB$$3ca31ce7;
    switch(var1.length) {
    case 0:
      var10000.<init>();
      CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
      return var10000;
    default:
      throw new IllegalArgumentException("Constructor not found");
    }
  }

  public Object newInstance(Callback[] var1) {
    CGLIB$SET_THREAD_CALLBACKS(var1);
    Bird$$EnhancerByCGLIB$$3ca31ce7 var10000 = new Bird$$EnhancerByCGLIB$$3ca31ce7();
    CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
    return var10000;
  }

  public void setCallbacks(Callback[] var1) {
    this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
  }

  public void setCallback(int var1, Callback var2) {
    switch(var1) {
    case 0:
      this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
    default:
    }
  }

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

  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 Callback[] getCallbacks() {
    CGLIB$BIND_CALLBACKS(this);
    return new Callback[]{this.CGLIB$CALLBACK_0};
  }

  public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
    CGLIB$STATIC_CALLBACKS = var0;
  }

  public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
    CGLIB$THREAD_CALLBACKS.set(var0);
  }

  static void CGLIB$STATICHOOK1() {
    CGLIB$THREAD_CALLBACKS = new ThreadLocal();
    CGLIB$emptyArgs = new Object[0];
    Class var0 = Class.forName("com.freedom.pattern.proxy.cglib.Bird$$EnhancerByCGLIB$$3ca31ce7");
    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$4");
    CGLIB$fly$0$Method = ReflectUtils.findMethods(new String[]{"fly", "()V"}, (var1 = Class.forName("com.freedom.pattern.proxy.cglib.Bird")).getDeclaredMethods())[0];
    CGLIB$fly$0$Proxy = MethodProxy.create(var1, var0, "()V", "fly", "CGLIB$fly$0");
  }

  private static final void CGLIB$BIND_CALLBACKS(Object var0) {
    Bird$$EnhancerByCGLIB$$3ca31ce7 var1 = (Bird$$EnhancerByCGLIB$$3ca31ce7)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];
    }

  }

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

  final int CGLIB$hashCode$3() {
    return super.hashCode();
  }

  final Object CGLIB$clone$4() throws CloneNotSupportedException {
    return super.clone();
  }

  final String CGLIB$toString$2() {
    return super.toString();
  }

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

  public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
    String var10000 = var0.toString();
    switch(var10000.hashCode()) {
    case -1271409118:
      if (var10000.equals("fly()V")) {
        return CGLIB$fly$0$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;
  }
}

8. 参考资料

• https://refactoringguru.cn/design-patterns/proxy