本将主要内容：
1. Actor引用、Actor路径

1. Actor引用、Actor路径

下图是Akka官方文档中给出的一张图
Akka并发编程——第四节：Actor模型（三） - 图1
该图清晰地说明了ActorPath，ActorRef，Actor及ActorSystem之间的关系，并说明了Actor整体的层次结构。前面我们提到，Akka应用程序会持有一个名称为user的Actor，该Actor被称为guardian supervisor（守卫监督器），无论是ActorSystem创建的Actor还是通过ActorContext创建的Actor都为user的子类，它是最顶级的Actor。

（一）ActorRef

对于ActorRef，我们已经很熟悉了，通过调用ActorSystem.actorOf方法可以创建Actor，返回的便是ActorRef，例如代码

  1. //创建FirstActor对象
  2.   val myactor = system.actorOf(Props[FirstActor], name = "firstActor")

返回的便是FirstActor的ActorRef对象，ActorRef最重要的作用便是向Actor发送消息，例如

  1. //向myactor发送消息
  2. myactor!"test"
  3. myactor! 123

另外，还可以通过context隐式对象获取父Actor和子Actor的ActorRef，示例代码如下：

  1. /*
  2. *Actor API:成员变量self及sender()方法的使用
  3. */
  4. object Example_07 extends App{
  5.   import akka.actor.Actor
  6.   import akka.actor.ActorSystem
  7.   import akka.actor.Props
  8.   class FirstActor extends Actor with ActorLogging{
  9.     //通过context.actorOf方法创建Actor
  10.     var child:ActorRef = _
  11.     override def preStart(): Unit ={
  12.       log.info("preStart() in FirstActor")
  13.       //通过context上下文创建Actor
  14.       child = context.actorOf(Props[MyActor], name = "myActor")
  15.     }
  16.     def receive = {
  17.       //向MyActor发送消息
  18.       case x => child ! x;log.info("received "+x)
  19.     }
  20.   }
  21.   class MyActor extends Actor with ActorLogging{
  22.     var parentActorRef:ActorRef=_
  23.     override def preStart(): Unit ={
  24.       //通过context.parent获取其父Actor的ActorRef
  25.       parentActorRef=context.parent
  26.     }
  27.     def receive = {
  28.       case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
  29.       case _      => log.info("received unknown message");
  30.     }
  31.   }
  32.   val system = ActorSystem("MyActorSystem")
  33.   val systemLog=system.log
  34.   //创建FirstActor对象
  35.   val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
  36.   //获取ActorPath
  37.   val myActorPath=system.child("firstActor")
  38.   //通过system.actorSelection方法获取ActorRef
  39.   val myActor1=system.actorSelection(myActorPath)
  40.   systemLog.info("准备向myactor发送消息")
  41.   //向myActor1发送消息
  42.   myActor1!"test"
  43.   myActor1! 123
  44.   Thread.sleep(5000)
  45.   //关闭ActorSystem，停止程序的运行
  46.   system.shutdown()
  47. }

代码运行结果

  1. [INFO] [04/02/2016 20:28:08.941] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
  2. [INFO] [04/02/2016 20:28:08.942] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
  3. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test
  4. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received 123
  5. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test
  6. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
  7. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received message from ParentActorRef
  8. [INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

代码

  1. class MyActor extends Actor with ActorLogging{
  2.     var parentActorRef:ActorRef=_
  3.     override def preStart(): Unit ={
  4.       //通过context.parent获取其父Actor的ActorRef
  5.       parentActorRef=context.parent
  6.     }
  7.     def receive = {
  8.       case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
  9.       case _      => log.info("received unknown message");
  10.     }
  11.   }

中，使用

  1. //通过context.parent获取其父Actor的ActorRef
  2.       parentActorRef=context.parent

获取MyActor 的直接父Actor的ActorRef，在本例中为FirstActor，因为在FirstActor中，我们使用

  1. //通过context上下文创建Actor
  2.       child = context.actorOf(Props[MyActor], name = "myActor")

创建了MyActor，FirstActor便自动成为MyActor的直接Supervisor。如此便可以通过代码

  1. parentActorRef!"message from ParentActorRef"

发送消息。
另外，还可以通过

  1. //创建FirstActor对象
  2.   val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
  3.   //获取ActorPath
  4.   val myActorPath=system.child("firstActor")
  5.   //通过system.actorSelection方法获取ActorRef
  6.   val myActor1=system.actorSelection(myActorPath)

system.actorSelection(myActorPath)方法获取相应的ActorRef。然后再使用获取到的ActorRef向Acto发送消息

  1. //向myActor1发送消息
  2.   myActor1!"test"
  3.   myActor1! 123

现在，让我们来总结一下获取ActorRef的方法：
（1）通过ActorSystem的actorOf方法，不过这种方式是通过创建Actor，然后返回其ActorRef
（2）通过context.actorOf方法，这种方式也是通过创建Actor,然后返回其ActorRef
（3）通过context.parent、context.self、context.children方法获取当前Actor的父Actor、当前Actor及子Actor的ActorRef，这种方式是获取已经创建好的Actor的ActorRef
（4）通过val myActor1=system.actorSelection(myActorPath)方法来获取ActorRef，这种方式也是获取已经创建好的Actor的ActorRef

（二）ActorPath

在前面的例子中，我们通过

  1. val myActorPath=system.child("firstActor")

已经使用到了ActorPath。在Akka中，ActorPath采用统一资源定位符的方式进行组织，例如

  1. //本地ActorPath
  2. "akka://my-sys/user/service-a/worker1" 
  3. //远程ActorPath
  4. "akka.tcp://my-sys@host.example.com:5678/user/service-b"

本地ActorPath是Akka并发编程中的ActorPath表示方式，而远程ActorPath是Akka分布式编程中常用的ActorPath表示方式，”akka.tcp://my-sys@host.example.com:5678/user/service-b”中的TCP表示使用的是TCP协议，也可以使用UPD协议，使用UDP协议的远程ActorPath表示方式有如下形式

  1. "akka.udp://my-sys@host.example.com:5678/user/service-b"

ActorPath当中，akka.udp表示的是使用的协议，my-sys表示的是ActorSytem名称，host.example.com:5678为远程机器地址及端口，user为guardian supervisor，service-b为当前应用程序的顶级Actor（通过system.actorOf方法创建的）

  1. /*
  2. *ActorPath
  3. */
  4. object Example_08 extends App{
  5.   import akka.actor.Actor
  6.   import akka.actor.ActorSystem
  7.   import akka.actor.Props
  9.   class FirstActor extends Actor with ActorLogging {
  10.     //通过context.actorOf方法创建Actor
  11.     var child:ActorRef = _
  12.     override def preStart(): Unit ={
  13.       log.info("preStart() in FirstActor")
  14.       //通过context上下文创建Actor
  15.       child = context.actorOf(Props[MyActor], name = "myActor")
  16.     }
  17.     def receive = {
  18.       //向MyActor发送消息
  19.       case x => child ! x;log.info("received "+x)
  20.     }
  21.   }
  23.   class MyActor extends Actor with ActorLogging {
  24.     def receive = {
  25.       case "test" => log.info("received test");
  26.       case _      => log.info("received unknown message");
  27.     }
  28.   }
  30.   val system = ActorSystem("MyActorSystem")
  31.   val systemLog=system.log
  32.   //创建FirstActor对象
  33.   val firstactor = system.actorOf(Props[FirstActor], name = "firstActor")
  34.   //获取ActorPath
  35.   val firstActorPath=system.child("firstActor")
  36.   systemLog.info("firstActorPath--->{}",firstActorPath)
  37.   //通过system.actorSelection方法获取ActorRef
  38.   val myActor1=system.actorSelection(firstActorPath)
  39.   //直接指定其路径
  40.   val myActor2=system.actorSelection("/user/firstActor")
  41.   //使用相对路径
  42.   val myActor3=system.actorSelection("../firstActor")
  43.   systemLog.info("准备向myactor发送消息")
  44.   //向myActor1发送消息
  45.   myActor2!"test"
  46.   myActor2! 123
  47.   Thread.sleep(5000)
  48.   //关闭ActorSystem，停止程序的运行
  49.   system.shutdown()
  50. }

代码运行结果：

  1. [INFO] [04/02/2016 21:04:59.612] [main] [ActorSystem(MyActorSystem)] firstActorPath--->akka://MyActorSystem/user/firstActor
  2. [INFO] [04/02/2016 21:04:59.612] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
  3. [INFO] [04/02/2016 21:04:59.615] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
  4. [INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test
  5. [INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received 123
  6. [INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myActor] received test
  7. [INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

本例中的重点代码如下

  1. //获取ActorPath
  2. val firstActorPath=system.child("firstActor")
  3. systemLog.info("myActorPath--->{}",firstActorPath)
  4. //通过system.actorSelection方法获取ActorRef
  5. val myActor1=system.actorSelection(firstActorPath)
  6. //直接指定其路径
  7. val myActor2=system.actorSelection("/user/firstActor")
  8. //使用相对路径
  9. val myActor3=system.actorSelection("../firstActor")

通过 val firstActorPath=system.child(“firstActor”)构造一个ActorPath，然后使用

  1. val myActor1=system.actorSelection(firstActorPath)

获取路径下的ActorRef，除这种方式外，还可以通过绝对路径 val myActor2=system.actorSelection(“/user/firstActor”)及相对路径 val myActor3=system.actorSelection(“../firstActor”)的方式获取ActorRef
，需要注意的是绝对路径使用的是guardian supevisor，即/user/firstActor的这种方式。如果要获取myActor，则基方法是类型的，例如

  1. //获取ActorPath
  2. val myActorPath=system.child("firstActor").child("myActor")
  3. systemLog.info("firstActorPath--->{}",myActorPath)
  4. //通过system.actorSelection方法获取ActorRef
  5. val myActor1=system.actorSelection(myActorPath)
  6. //直接指定其路径
  7. val myActor2=system.actorSelection("/user/firstActor/myActor")
  8. //使用相对路径
  9. val myActor3=system.actorSelection("../firstActor/myActor")

完整代码如下：

  1. /*
  2. *ActorPath，获取myActor
  3. */
  4. object Example_09 extends App{
  5.   import akka.actor.Actor
  6.   import akka.actor.ActorSystem
  7.   import akka.actor.Props
  8.   class FirstActor extends Actor with ActorLogging{
  9.     //通过context.actorOf方法创建Actor
  10.     var child:ActorRef = _
  11.     override def preStart(): Unit ={
  12.       log.info("preStart() in FirstActor")
  13.       //通过context上下文创建Actor
  14.       child = context.actorOf(Props[MyActor], name = "myActor")
  15.     }
  16.     def receive = {
  17.       //向MyActor发送消息
  18.       case x => child ! x;log.info("received "+x)
  19.     }
  20.   }
  21.   class MyActor extends Actor with ActorLogging{
  22.     def receive = {
  23.       case "test" => log.info("received test");
  24.       case _      => log.info("received unknown message");
  25.     }
  26.   }
  27.   val system = ActorSystem("MyActorSystem")
  28.   val systemLog=system.log
  29.   //创建FirstActor对象
  30.   val firstactor = system.actorOf(Props[FirstActor], name = "firstActor")
  31.   //获取ActorPath
  32.   val myActorPath=system.child("firstActor").child("myActor")
  33.   systemLog.info("firstActorPath--->{}",myActorPath)
  34.   //通过system.actorSelection方法获取ActorRef
  35.   val myActor1=system.actorSelection(myActorPath)
  36.   //直接指定其路径
  37.   val myActor2=system.actorSelection("/user/firstActor/myActor")
  38.   //使用相对路径
  39.   val myActor3=system.actorSelection("../firstActor/myActor")
  40.   systemLog.info("准备向myactor发送消息")
  41.   //向myActor1发送消息
  42.   myActor1!"test"
  43.   myActor1! 123
  44.   Thread.sleep(5000)
  45.   //关闭ActorSystem，停止程序的运行
  46.   system.shutdown()
  47. }

代码运行结果：

  1. [INFO] [04/02/2016 21:21:14.377] [main] [ActorSystem(MyActorSystem)] firstActorPath--->akka://MyActorSystem/user/firstActor/myActor
  2. [INFO] [04/02/2016 21:21:14.377] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
  3. [INFO] [04/02/2016 21:21:14.381] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
  4. [INFO] [04/02/2016 21:21:14.382] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test
  5. [INFO] [04/02/2016 21:21:14.382] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

关于远程ActorRef的获取，我们将在后续章节中进行讲述。