Java动态代理

通过以下几种方式介绍动态代理

  • 动态代理涉及到的类
  • 动态代理用法
  • Proxy类解析
  • 动态代理类解析
动态代理涉及到的类
InvocationHandler(Interface)// 处理类
    //参数-> 代理类对象,被代理类的方法,被代理类方法参数(MyInvocationHandler 类中有印证)
    //返回值-> 被代理类方法返回结果
    public Object invoke(Object proxy, Method method, Object[] args)
 
Proxy(Class)// 动态创建一个代理对象的类
     // 参数->类加载器,被代理类实现的接口,InvocationHandler 实现类
     // 返回值->代理类(动态生成)
     public static Object newProxyInstance(ClassLoader loader,Class[] interfaces,InvocationHandler h)
     // 参数->类加载器,被代理类实现的接口
     // 返回值->未被实例化的代理类(构造器参数类型为InvocationHandler)
     public static Class getProxyClass(ClassLoader loader,Class... interfaces)
动态代理用法
public class Test {

public static void main(String[] args) throws Exception{
    proxyTest1();// 方法一
    proxyTest2();// 方法二
}

// 动态代理方法一
private static void proxyTest1() {
    // 创建订单方法
    OrderInterface order = new OrderService();

    InvocationHandler invocationHandler = getInvocationHandler(order);

    /**
     * Proxy.newProxyInstance 方法三个参数
     *  ClassLoader loader 类加载器
     *  Class[] interfaces 订单类接口
     *  InvocationHandler h 处理器(内含增强方法-打印处理订单日志)
     *
     *  通过类加载器和订单类接口动态创建代理类,
     *  然后将处理器设置进动态代理类,
     *  返回实现订单类接口的动态代理实现类(动态生成)
     *
     * */
    OrderInterface orderInterface = (OrderInterface)Proxy.newProxyInstance(order.getClass().getClassLoader(), order.getClass().getInterfaces(), invocationHandler);

    orderInterface.createOrder(new OrderInfo());
}
// 动态代理方法二
private static void proxyTest2() throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
    // 创建订单方法
    OrderInterface order = new OrderService();

    InvocationHandler invocationHandler = getInvocationHandler(order);
    /**
     * ClassLoader loader 类加载器
     * Class... interfaces 订单类接口
     *
     * 通过类加载器和订单类接口动态创建代理类
     * */
    Class clazz = Proxy.getProxyClass(order.getClass().getClassLoader(), order.getClass().getInterfaces());
    /**
     * 获取参数为InvocationHandler类型的构造器
     * */
    Constructor constructor = clazz.getConstructor(InvocationHandler.class);
    /**
     * 将处理器传进参数里,实例化类,进行调用以达到增强方法的目的
     * */
    OrderInterface orderInterface = (OrderInterface)constructor.newInstance(invocationHandler);

    orderInterface.createOrder(new OrderInfo());
}

// InvocationHandler 处理器
private static InvocationHandler getInvocationHandler(OrderInterface order) {
    // 内部实现InvocationHandler接口,增强被代理类方法功能
    InvocationHandler invocationHandler = new MyInvocationHandler(order);
    return invocationHandler;
}
}

处理类

public class MyInvocationHandler implements InvocationHandler {

  private Object object;

  public MyInvocationHandler(Object object) {
      this.object = object;
  }

   public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println(new StringBuilder("Object proxy-->className:").append(proxy.getClass().getName()));
        System.out.println(new StringBuilder("Method method-->methodName:").append(method.getName()));
        if (null != args && args.length > 0) {
            System.out.println(new StringBuilder("Object[] args-->paramValue:").append(args[0].toString()));
        }

         System.out.println(new StringBuilder("增强方法:").append("记录日志...").toString());

         Object returnObject = method.invoke(object, args);

         return returnObject;
   }
}

订单类接口

 public interface OrderInterface {
   public void createOrder(OrderInfo order);
}

订单处理类(执行下单流程)

public class OrderService implements OrderInterface {

  public void createOrder(OrderInfo order) {
    System.out.print("创建订单");

    try {
        for (int i = 0; i < 3; i++) {
            Thread.sleep(500);
            System.out.print(".");
        }

    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println("");
    System.out.println("订单创建成功");
}
}

实体类

public class OrderInfo {
     @Override
     public String toString() {
         return "ClassName-->OrderInfo";
      }
}
Proxy类解析

属性及构造器

// 构造器参数类型
private static final Class[] constructorParams = { InvocationHandler.class };
// 代理类缓存,采用弱引用方式进行缓存,方便jvm进行gc垃圾回收
private static final WeakCache[], Class> proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());
// 处理类,通过构造器进行赋值。1:子类继承Proxy类,构造器赋值,2:Proxy.newProxyInstance()调用该方法生成代理类,利用反射创建代理类进行构造器赋值
protected InvocationHandler h;
// 提供的两种构造器限制了我们使用Proxy类只能直接调用静态方法
private Proxy() {
}
// 创建动态代理类会使用到该构造器
protected Proxy(InvocationHandler h) {
    this.h = h;
}

方法

// 获取代理类(在文章开头有介绍此方法)。
public static Class getProxyClass(ClassLoader loader, Class... interfaces)  throws IllegalArgumentException
{
    final Class[] intfs = interfaces.clone();
    final SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
        checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
    }
    // 获取代理类
    return getProxyClass0(loader, intfs);
}

// 获取代理类,并且生成代理类实例(在文章开头有介绍此方法)。
public static Object newProxyInstance(ClassLoader loader, Class[] interfaces, InvocationHandler h) throws IllegalArgumentException
{
   // 代码和getProxyClass方法目的一致,获取动态代理类。
    -------------------------------------------------------------------------
    Objects.requireNonNull(h);
    final Class[] intfs = interfaces.clone();
    final SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
        checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
    }
    Class cl = getProxyClass0(loader, intfs);
    -------------------------------------------------------------------------
    try {
        if (sm != null) {
            checkNewProxyPermission(Reflection.getCallerClass(), cl);
        }
        // 通过反射获取参数为InvocationHandler类型的构造器
        final Constructor cons = cl.getConstructor(constructorParams);
        final InvocationHandler ih = h;
       
        if (!Modifier.isPublic(cl.getModifiers())) {
            AccessController.doPrivileged(new PrivilegedAction() {
                public Void run() {
                    cons.setAccessible(true);
                    return null;
                }
            });
        }
        // 实例化动态代理类,并指定构造器参数
        return cons.newInstance(new Object[]{h});
    } catch (IllegalAccessException|InstantiationException e) {
        throw new InternalError(e.toString(), e);
    } catch (InvocationTargetException e) {
        Throwable t = e.getCause();
        if (t instanceof RuntimeException) {
            throw (RuntimeException) t;
        } else {
            throw new InternalError(t.toString(), t);
        }
    } catch (NoSuchMethodException e) {
        throw new InternalError(e.toString(), e);
    }
}  

// 生成动态代理类
private static Class getProxyClass0(ClassLoader loader, Class... interfaces) {
    if (interfaces.length > 65535) {
        throw new IllegalArgumentException("interface limit exceeded");
    }

    // 代理类的获取及创建(使用了弱引用方式)
    return proxyClassCache.get(loader, interfaces);
}
动态代理类解析(生成代理类方法在git中)
// ProxyObject 随意指定的一个类名,该类继承了Proxy(构造赋值),实现了OrderInterface接口(实现代理方法)
public final class ProxyObject extends Proxy implements 
{
  private static Method m1;
  private static Method m3;
  private static Method m2;
  private static Method m0;
  // 代理类构造,参数为InvocationHandler 类型。上文介绍了,Proxy 类InvocationHandler 赋值第一种方式:子类继承Proxy类,构造器赋值
  public ProxyObject(InvocationHandler paramInvocationHandler)
  {
    super(paramInvocationHandler);
  }

  static
   {
     try
     {
       // 反射生成方法内所有方法的Method对象
       m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
       m3 = Class.forName("proxy.OrderInterface").getMethod("createOrder", new Class[] { Class.forName("proxy.OrderInfo") });
       m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
       m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
       return;
     }
     catch (NoSuchMethodException localNoSuchMethodException)
     {
       throw new      NoSuchMethodError(localNoSuchMethodException.getMessage());
     }
     catch (ClassNotFoundException localClassNotFoundException)
     {
       throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
     }
   }
  // 创建订单方法(代理方法)
  public final void createOrder(OrderInfo paramOrderInfo)
  {
    try
    {
      // 执行InvocationHandler实现类的invoke方法(方法参数在文章开头有介绍)。
      this.h.invoke(this, m3, new Object[] { paramOrderInfo });
      return;
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final boolean equals(Object paramObject)
  {
    try
    {
      return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  public final String toString()
  {
    try
    {
      return (String)this.h.invoke(this, m2, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }
  //hashCode()   略
 }

代码地址:https://gitee.com/chenxu_jdk/proxy-test

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