Akka并发编程——第四节：Actor模型（三）

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

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

 //创建FirstActor对象
  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

//向myactor发送消息
myactor!"test"
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：

/*
*Actor API:成员变量self及sender()方法的使用
*/
object Example_07 extends App{
  import akka.actor.Actor
  import akka.actor.ActorSystem
  import akka.actor.Props

  class FirstActor extends Actor with ActorLogging{
    //通过context.actorOf方法创建Actor
    var child:ActorRef = _
    override def preStart(): Unit ={
      log.info("preStart() in FirstActor")
      //通过context上下文创建Actor
      child = context.actorOf(Props[MyActor], name = "myActor")
    }
    def receive = {
      //向MyActor发送消息
      case x => child ! x;log.info("received "+x)
    }
  }

  class MyActor extends Actor with ActorLogging{
    var parentActorRef:ActorRef=_
    override def preStart(): Unit ={
      //通过context.parent获取其父Actor的ActorRef
      parentActorRef=context.parent
    }
    def receive = {
      case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
      case _      => log.info("received unknown message");
    }

  }
  val system = ActorSystem("MyActorSystem")
  val systemLog=system.log

  //创建FirstActor对象
  val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
  //获取ActorPath
  val myActorPath=system.child("firstActor")
  //通过system.actorSelection方法获取ActorRef
  val myActor1=system.actorSelection(myActorPath)
  systemLog.info("准备向myactor发送消息")
  //向myActor1发送消息
  myActor1!"test"
  myActor1! 123
  Thread.sleep(5000)
  //关闭ActorSystem，停止程序的运行
  system.shutdown()
}

代码运行结果

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

代码

 class MyActor extends Actor with ActorLogging{
    var parentActorRef:ActorRef=_
    override def preStart(): Unit ={
      //通过context.parent获取其父Actor的ActorRef
      parentActorRef=context.parent
    }
    def receive = {
      case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
      case _      => log.info("received unknown message");
    }

  }

中，使用

//通过context.parent获取其父Actor的ActorRef
      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

 //通过context上下文创建Actor
      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

parentActorRef!"message from ParentActorRef"

发送消息。

另外，还可以通过

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

 //向myActor1发送消息
  myActor1!"test"
  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

 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

//本地ActorPath
"akka://my-sys/user/service-a/worker1" 
//远程ActorPath
"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

"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）

/*
*ActorPath
*/
object Example_08 extends App{
  import akka.actor.Actor
  import akka.actor.ActorSystem
  import akka.actor.Props

  class FirstActor extends Actor with ActorLogging{
    //通过context.actorOf方法创建Actor
    var child:ActorRef = _
    override def preStart(): Unit ={
      log.info("preStart() in FirstActor")
      //通过context上下文创建Actor
      child = context.actorOf(Props[MyActor], name = "myActor")
    }
    def receive = {
      //向MyActor发送消息
      case x => child ! x;log.info("received "+x)
    }
  }

  class MyActor extends Actor with ActorLogging{
    def receive = {
      case "test" => log.info("received test");
      case _      => log.info("received unknown message");
    }

  }
  val system = ActorSystem("MyActorSystem")
  val systemLog=system.log

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

  //获取ActorPath
  val firstActorPath=system.child("firstActor")
  systemLog.info("firstActorPath--->{}",firstActorPath)


  //通过system.actorSelection方法获取ActorRef
  val myActor1=system.actorSelection(firstActorPath)

  //直接指定其路径
  val myActor2=system.actorSelection("/user/firstActor")
  //使用相对路径
  val myActor3=system.actorSelection("../firstActor")


  systemLog.info("准备向myactor发送消息")
  //向myActor1发送消息
  myActor2!"test"
  myActor2! 123
  Thread.sleep(5000)
  //关闭ActorSystem，停止程序的运行
  system.shutdown()
}

代码运行结果：

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

//获取ActorPath
  val firstActorPath=system.child("firstActor")
  systemLog.info("myActorPath--->{}",firstActorPath)


  //通过system.actorSelection方法获取ActorRef
  val myActor1=system.actorSelection(firstActorPath)

  //直接指定其路径
  val myActor2=system.actorSelection("/user/firstActor")
  //使用相对路径
  val myActor3=system.actorSelection("../firstActor")

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

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

//获取ActorPath
  val myActorPath=system.child("firstActor").child("myActor")
  systemLog.info("firstActorPath--->{}",myActorPath)


  //通过system.actorSelection方法获取ActorRef
  val myActor1=system.actorSelection(myActorPath)

  //直接指定其路径
  val myActor2=system.actorSelection("/user/firstActor/myActor")
  //使用相对路径
  val myActor3=system.actorSelection("../firstActor/myActor")

完整代码如下：

/*
*ActorPath，获取myActor
*/
object Example_09 extends App{
  import akka.actor.Actor
  import akka.actor.ActorSystem
  import akka.actor.Props

  class FirstActor extends Actor with ActorLogging{
    //通过context.actorOf方法创建Actor
    var child:ActorRef = _
    override def preStart(): Unit ={
      log.info("preStart() in FirstActor")
      //通过context上下文创建Actor
      child = context.actorOf(Props[MyActor], name = "myActor")
    }
    def receive = {
      //向MyActor发送消息
      case x => child ! x;log.info("received "+x)
    }
  }

  class MyActor extends Actor with ActorLogging{
    def receive = {
      case "test" => log.info("received test");
      case _      => log.info("received unknown message");
    }

  }
  val system = ActorSystem("MyActorSystem")
  val systemLog=system.log

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

  //获取ActorPath
  val myActorPath=system.child("firstActor").child("myActor")
  systemLog.info("firstActorPath--->{}",myActorPath)


  //通过system.actorSelection方法获取ActorRef
  val myActor1=system.actorSelection(myActorPath)

  //直接指定其路径
  val myActor2=system.actorSelection("/user/firstActor/myActor")
  //使用相对路径
  val myActor3=system.actorSelection("../firstActor/myActor")


  systemLog.info("准备向myactor发送消息")
  //向myActor1发送消息
  myActor1!"test"
  myActor1! 123
  Thread.sleep(5000)
  //关闭ActorSystem，停止程序的运行
  system.shutdown()
}

代码运行结果：

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

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