Question

我们有域对象扩展抽象基类以支持时间戳

abstract class TimestampedObject {
    private Date timestamp;
    public Date getTimestamp(){return timestamp;}
    public void setTimestamp(final Date timestamp){this.timestamp = timestamp;}
}

但这会使我们的等级混乱。

我们可以使用Spring AOP介绍或Aspectj ITD来实现这一目标吗？

Answer 1

AspectJ in Action书中的一个例子（来自未经测试的内存）将会是这样的：

public interface Timestamped {
   long getTimestamp();
   void setTimestamp();

   public static interface Impl extends Timestamped {
        public static aspect Implementation {
              private long Timestamped.Impl.timestamp;
              public long Timestamped.Impl.getTimestamp(){ return timestamp; }
              public void Timestamped.Impl.setTimestamp(long in) { timestamp = in; }
        }          
   }

   //and then your classes would use it like this:
   public class SomeClass implements Timestamped.Impl {

           private void someFunc() {
              setTimestamp(12);
              long t = getTimestamp();
           }
    }

不确定这本书是否有这种方式，但我通常创建一个单独的Impl接口（如上所示），只扩展主要接口，这样我的一些类可以以不同方式实现时间戳，而无需获取ITD实现。像这样：

public class SomeOtherClass implements Timestamped {
       private long myOwnPreciousTimestamp;

       public long getTimestamp() {
            //Oh! I don't know should I give it to you?!
            //I know, I will only give you a half of my timestamp
            return myOwnPreciousTimestamp/2;
       }

       //etc.....
}

Answer 2

是的，这是exactly what ITDs are for。

我可以使用类型间声明来添加属性吗？

2 个答案: