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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