Java设计模式之代理模式的动态代理上篇

前言

什么是动态代理呢？动态代理指的是在实现阶段不需要关心代理谁，而是在运行阶段才指定哪一个对象。

动态代理示例

首先要介绍一下JDK提供的一个动态代理接口 InvocationHandler。这个接口的用途在于对代理类的方法进行代理，我们先实现InvocationHandler接口：

public class ConsumerHandler implements InvocationHandler {

    private Object proxiedInstance = null;

    public ConsumerHandler(Object proxiedInstance) {
        this.proxiedInstance = proxiedInstance;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        Object proxyInstance = method.invoke(this.proxiedInstance, args);
        return proxyInstance;
    }
}

第3行：声明被代理的对象实例。

第5行：构造行数被代理对象作为形式参数。

第10行-14行：调用被代理的方法。

消费者抽象接口和消费者真实角色都没有改动，代码如下图所示：

public interface IConsumer {

    public void login(String name, String password);

    public void order();

    public void pay();

}

public class RealConsumer implements IConsumer {

    private String name = null;

    public RealConsumer(String name){
        this.name = name;
    }

    @Override
    public void login(String name, String password) {

        System.out.println("登录用户["+name+"]登陆成功");
    }

    @Override
    public void order() {

        System.out.println("登录账号："+ this.name +"生成订单成功");

    }

    @Override
    public void pay() {

        System.out.println("登录账号："+ this.name +"订单支付成功");

    }

}

OK。这个都没什么问题，最后我们再看看一下动态代理的场景类：

public class Client {

    public static void main(String[] args) {
        IConsumer consumer = new RealConsumer("抒尽");

        ConsumerHandler consumerHandler = new ConsumerHandler(consumer);

        ClassLoader classLoader = consumer.getClass().getClassLoader();

        Object o = Proxy.newProxyInstance(classLoader, new Class[]{IConsumer.class}, consumerHandler);
        IConsumer proxy = (IConsumer)o;

        proxy.login("shujin", "123456");
        proxy.order();
        proxy.pay();
    }
}

第4行，定义一个真实消费者[抒尽]

第6行，定义一个handler

第8行，获取真实角色的类加载器

第10行-11行，动态产生一个代理者

第13行-15行，使用代理者来访问。

使用动态代理，我们并没有手工去创建一个代理类，更加没有代理类实现抽象接口。这就是动态代理的强大功能，如果我们需要变更需求，只需要修改动态代理实现类即可。

如果使用InvovationHandler实现动态代理。要产生某个类的代理，这个类必须要有接口。

如何查看动态代理类

下面我们来看一下这个代理类产生的class文件。首先我们在场景类中main方法中增加系统参数：System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

public static void main(String[] args) {

        System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");

        IConsumer consumer = new RealConsumer("抒尽");

        ConsumerHandler consumerHandler = new ConsumerHandler(consumer);

        ClassLoader classLoader = consumer.getClass().getClassLoader();

        Object o = Proxy.newProxyInstance(classLoader, new Class[]{IConsumer.class}, consumerHandler);
        IConsumer proxy = (IConsumer)o;

        proxy.login("shujin", "123456");
        proxy.order();
        proxy.pay();
    }

 执行main方法之后，在项目的../com/sun/proxy目录下，会产生一个叫作$Proxy0.class。通过javap -c $Proxy0.class查看文件的字节码：

public final class com.sun.proxy.$Proxy0 extends java.lang.reflect.Proxy implements com.example.pattern.proxy.dynamic.IConsumer {
  public com.sun.proxy.$Proxy0(java.lang.reflect.InvocationHandler) throws ;
    Code:
       0: aload_0
       1: aload_1
       2: invokespecial #8                  // Method java/lang/reflect/Proxy."<init>":(Ljava/lang/reflect/InvocationHandler;)V
       5: return

  public final boolean equals(java.lang.Object) throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #20                 // Field m1:Ljava/lang/reflect/Method;
       8: iconst_1
       9: anewarray     #22                 // class java/lang/Object
      12: dup
      13: iconst_0
      14: aload_1
      15: aastore
      16: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      21: checkcast     #30                 // class java/lang/Boolean
      24: invokevirtual #34                 // Method java/lang/Boolean.booleanValue:()Z
      27: ireturn
      28: athrow
      29: astore_2
      30: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      33: dup
      34: aload_2
      35: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      38: athrow
    Exception table:
       from    to  target type
           0    28    28   Class java/lang/Error
           0    28    28   Class java/lang/RuntimeException
           0    28    29   Class java/lang/Throwable

  public final void pay() throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #50                 // Field m5:Ljava/lang/reflect/Method;
       8: aconst_null
       9: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      14: pop
      15: return
      16: athrow
      17: astore_1
      18: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      21: dup
      22: aload_1
      23: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      26: athrow
    Exception table:
       from    to  target type
           0    16    16   Class java/lang/Error
           0    16    16   Class java/lang/RuntimeException
           0    16    17   Class java/lang/Throwable

  public final void order() throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #54                 // Field m3:Ljava/lang/reflect/Method;
       8: aconst_null
       9: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      14: pop
      15: return
      16: athrow
      17: astore_1
      18: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      21: dup
      22: aload_1
      23: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      26: athrow
    Exception table:
       from    to  target type
           0    16    16   Class java/lang/Error
           0    16    16   Class java/lang/RuntimeException
           0    16    17   Class java/lang/Throwable

  public final java.lang.String toString() throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #59                 // Field m2:Ljava/lang/reflect/Method;
       8: aconst_null
       9: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      14: checkcast     #61                 // class java/lang/String
      17: areturn
      18: athrow
      19: astore_1
      20: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      23: dup
      24: aload_1
      25: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      28: athrow
    Exception table:
       from    to  target type
           0    18    18   Class java/lang/Error
           0    18    18   Class java/lang/RuntimeException
           0    18    19   Class java/lang/Throwable

  public final void login(java.lang.String, java.lang.String) throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #66                 // Field m4:Ljava/lang/reflect/Method;
       8: iconst_2
       9: anewarray     #22                 // class java/lang/Object
      12: dup
      13: iconst_0
      14: aload_1
      15: aastore
      16: dup
      17: iconst_1
      18: aload_2
      19: aastore
      20: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      25: pop
      26: return
      27: athrow
      28: astore_3
      29: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      32: dup
      33: aload_3
      34: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      37: athrow
    Exception table:
       from    to  target type
           0    27    27   Class java/lang/Error
           0    27    27   Class java/lang/RuntimeException
           0    27    28   Class java/lang/Throwable

  public final int hashCode() throws ;
    Code:
       0: aload_0
       1: getfield      #16                 // Field java/lang/reflect/Proxy.h:Ljava/lang/reflect/InvocationHandler;
       4: aload_0
       5: getstatic     #71                 // Field m0:Ljava/lang/reflect/Method;
       8: aconst_null
       9: invokeinterface #28,  4           // InterfaceMethod java/lang/reflect/InvocationHandler.invoke:(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/la
ng/Object;)Ljava/lang/Object;
      14: checkcast     #73                 // class java/lang/Integer
      17: invokevirtual #76                 // Method java/lang/Integer.intValue:()I
      20: ireturn
      21: athrow
      22: astore_1
      23: new           #42                 // class java/lang/reflect/UndeclaredThrowableException
      26: dup
      27: aload_1
      28: invokespecial #45                 // Method java/lang/reflect/UndeclaredThrowableException."<init>":(Ljava/lang/Throwable;)V
      31: athrow
    Exception table:
       from    to  target type
           0    21    21   Class java/lang/Error
           0    21    21   Class java/lang/RuntimeException
           0    21    22   Class java/lang/Throwable

  static {} throws ;
    Code:
       0: ldc           #79                 // String java.lang.Object
       2: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
       5: ldc           #86                 // String equals
       7: iconst_1
       8: anewarray     #81                 // class java/lang/Class
      11: dup
      12: iconst_0
      13: ldc           #79                 // String java.lang.Object
      15: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      18: aastore
      19: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
      22: putstatic     #20                 // Field m1:Ljava/lang/reflect/Method;
      25: ldc           #92                 // String com.example.pattern.proxy.dynamic.IConsumer
      27: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      30: ldc           #93                 // String pay
      32: iconst_0
      33: anewarray     #81                 // class java/lang/Class
      36: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
      39: putstatic     #50                 // Field m5:Ljava/lang/reflect/Method;
      42: ldc           #92                 // String com.example.pattern.proxy.dynamic.IConsumer
      44: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      47: ldc           #94                 // String order
      49: iconst_0
      50: anewarray     #81                 // class java/lang/Class
      53: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
      56: putstatic     #54                 // Field m3:Ljava/lang/reflect/Method;
      59: ldc           #79                 // String java.lang.Object
      61: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      64: ldc           #95                 // String toString
      66: iconst_0
      67: anewarray     #81                 // class java/lang/Class
      70: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
      73: putstatic     #59                 // Field m2:Ljava/lang/reflect/Method;
      76: ldc           #92                 // String com.example.pattern.proxy.dynamic.IConsumer
      78: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      81: ldc           #96                 // String login
      83: iconst_2
      84: anewarray     #81                 // class java/lang/Class
      87: dup
      88: iconst_0
      89: ldc           #98                 // String java.lang.String
      91: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
      94: aastore
      95: dup
      96: iconst_1
      97: ldc           #98                 // String java.lang.String
      99: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
     102: aastore
     103: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
     106: putstatic     #66                 // Field m4:Ljava/lang/reflect/Method;
     109: ldc           #79                 // String java.lang.Object
     111: invokestatic  #85                 // Method java/lang/Class.forName:(Ljava/lang/String;)Ljava/lang/Class;
     114: ldc           #99                 // String hashCode
     116: iconst_0
     117: anewarray     #81                 // class java/lang/Class
     120: invokevirtual #90                 // Method java/lang/Class.getMethod:(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
     123: putstatic     #71                 // Field m0:Ljava/lang/reflect/Method;
     126: return
     127: astore_1
     128: new           #103                // class java/lang/NoSuchMethodError
     131: dup
     132: aload_1
     133: invokevirtual #106                // Method java/lang/Throwable.getMessage:()Ljava/lang/String;
     136: invokespecial #109                // Method java/lang/NoSuchMethodError."<init>":(Ljava/lang/String;)V
     139: athrow
     140: astore_1
     141: new           #113                // class java/lang/NoClassDefFoundError
     144: dup
     145: aload_1
     146: invokevirtual #106                // Method java/lang/Throwable.getMessage:()Ljava/lang/String;
     149: invokespecial #114                // Method java/lang/NoClassDefFoundError."<init>":(Ljava/lang/String;)V
     152: athrow
    Exception table:
       from    to  target type
           0   127   127   Class java/lang/NoSuchMethodException
           0   127   140   Class java/lang/ClassNotFoundException
}

生成的信息比较多，看不懂也没有太大关系，我们挑主要的看。

第1行，$Proxy0继承自Proxy同时实现接口IConsumer。Proxy类是给创建动态代理时提供了静态的方法，同时也是所有代理类的超类。同时实现了接口IConsumer。这个接口是被代理角色的接口，这也说明，使用JDK的InvocationHander动态代理时，被代理的具体角色一定要有抽象接口。

第9行，equals方法。

第63行，order方法。

第111行，login方法。

第144行，hashcode方法。

第169行，静态代码块。

1.被代理类的接口拥有的方法，代理类都会拥有，这个说明了：动态代理是根据被代理的接口生成所有的方法。换而言之，只要确定一个接口，动态代理会告诉我们我已经全部实现了你的所有方法。

2.静态代码块：初始化静态实例包括pay方法，order方法，login方法的Method实例，实例好之后代理类调用被代理类时使用method反射机制调用。我们可以使用idea直接打开class文件。

public final class $Proxy0 extends Proxy implements IConsumer {
    private static Method m1;
    private static Method m5;
    private static Method m3;
    private static Method m2;
    private static Method m4;
    private static Method m0;

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

    public final void login(String var1, String var2) throws  {
        try {
            super.h.invoke(this, m4, new Object[]{var1, var2});
        } catch (RuntimeException | Error var4) {
            throw var4;
        } catch (Throwable var5) {
            throw new UndeclaredThrowableException(var5);
        }
    }
    
    //此处省略其他方法...
 

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m5 = Class.forName("com.example.pattern.proxy.dynamic.IConsumer").getMethod("pay");
            m3 = Class.forName("com.example.pattern.proxy.dynamic.IConsumer").getMethod("order");
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m4 = Class.forName("com.example.pattern.proxy.dynamic.IConsumer").getMethod("login", Class.forName("java.lang.String"), Class.forName("java.lang.String"));
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

第26行，静态方法，通过类的反射机制得到Method。

第15行， super.h。父类是proxy。受保护的属性Invocation。然后再调用我们Invocation的实现类ConsumerHandler中的invoke方法。看到这里，应该都想到了吧，只要有扩展，我们只需要的invoke方法中去扩展，答应时间，增加日志等等。

Proxy中的受保护的属性InvocationHandler又是什么时候初始化进去的呢？Proxy中提供了一个静态方法newProxyInstance();public static Object newProxyInstance(ClassLoader loader,Class<?>[] interfaces,InvocationHandler h);实际上从根本上讲，这不就是创建一个代理的产品吗？这难道不就是弱化的工厂模式吗？