Akka并发编程——第三节：Actor模型（二）

本节主要内容：

1. Actor API解析

1. Actor API解析

Actor中的主要成员变量和方法定义如下：

package akka.actortrait Actor extends scala.AnyRef {  type Receive = akka.actor.Actor.Receive  //context变量暴露当前Actor的上下文信息及当前消息  implicit val context : akka.actor.ActorContext = { /* compiled code */ }  //self作为当前ActorRef的引用  implicit final val self : akka.actor.ActorRef = { /* compiled code */ }  //当前Actor接收到最后一条消息对应的消息发送者(Actor）  final def sender() : akka.actor.ActorRef = { /* compiled code */ }  //receive方法，抽象方法，定义Actor的行为逻辑  def receive : akka.actor.Actor.Receive  //内部使用API   protected[akka] def aroundReceive(receive : akka.actor.Actor.Receive, msg : scala.Any) : scala.Unit = { /* compiled code */ }  protected[akka] def aroundPreStart() : scala.Unit = { /* compiled code */ }  protected[akka] def aroundPostStop() : scala.Unit = { /* compiled code */ }  protected[akka] def aroundPreRestart(reason : scala.Throwable, message : scala.Option[scala.Any]) : scala.Unit = { /* compiled code */ }  protected[akka] def aroundPostRestart(reason : scala.Throwable) : scala.Unit = { /* compiled code */ }   //监督策略，用于Actor容错处理  def supervisorStrategy : akka.actor.SupervisorStrategy = { /* compiled code */ }  //Hook方法，用于Actor生命周期监控   @scala.throws[T](classOf[scala.Exception])  def preStart() : scala.Unit = { /* compiled code */ }  @scala.throws[T](classOf[scala.Exception])  def postStop() : scala.Unit = { /* compiled code */ }  @scala.throws[T](classOf[scala.Exception])  def preRestart(reason : scala.Throwable, message : scala.Option[scala.Any]) : scala.Unit = { /* compiled code */ }  @scala.throws[T](classOf[scala.Exception])  def postRestart(reason : scala.Throwable) : scala.Unit = { /* compiled code */ }  //发送给Actor的消息，Actor没有定义相应的处理逻辑时，会调用此方法  def unhandled(message : scala.Any) : scala.Unit = { /* compiled code */ }}object Actor extends scala.AnyRef {  type Receive = scala.PartialFunction[scala.Any, scala.Unit]  //空的行为逻辑  @scala.SerialVersionUID(1)  object emptyBehavior extends scala.AnyRef with akka.actor.Actor.Receive {    def isDefinedAt(x : scala.Any) : scala.Boolean = { /* compiled code */ }    def apply(x : scala.Any) : scala.Nothing = { /* compiled code */ }  }  //Sender为null  @scala.SerialVersionUID(1)  final val noSender : akka.actor.ActorRef = { /* compiled code */ }}
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（1） Hook方法，preStart()、postStop()方法的使用

/* *Actor API: Hook方法 */  object Example_05 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 = _      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作      override def preStart(): Unit ={        log.info("preStart() in FirstActor")        //通过context上下文创建Actor        child = context.actorOf(Props[MyActor], name = "myChild")      }      def receive = {        //向MyActor发送消息        case x => child ! x;log.info("received "+x)      }      //Hook方法，postStop()，Actor停止之后调用      override def postStop(): Unit = {        log.info("postStop() in FirstActor")       }    }    class MyActor extends Actor with ActorLogging{      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作      override def preStart(): Unit ={        log.info("preStart() in MyActor")      }      def receive = {        case "test" => log.info("received test")        case _      => log.info("received unknown message")      }      //Hook方法，postStop()，Actor停止之后调用      override def postStop(): Unit = {        log.info("postStop() in MyActor")      }    }    val system = ActorSystem("MyActorSystem")    val systemLog=system.log    //创建FirstActor对象    val myactor = system.actorOf(Props[FirstActor], name = "firstActor")    systemLog.info("准备向myactor发送消息")    //向myactor发送消息    myactor!"test"    myactor! 123    Thread.sleep(5000)    //关闭ActorSystem，停止程序的运行    system.shutdown()  }
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代码运行结果：

[INFO] [04/02/2016 17:04:49.607] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test[INFO] [04/02/2016 17:04:49.607] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received 123[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] preStart() in MyActor[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] received test[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] received unknown message[INFO] [04/02/2016 17:04:54.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myChild] postStop() in MyActor[INFO] [04/02/2016 17:04:54.617] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] postStop() in FirstActor

在代码

 class FirstActor extends Actor with ActorLogging{      //通过context.actorOf方法创建Actor      var child:ActorRef = _      //Hook方法，preStart()，Actor启动之前调用，用于完成初始化工作      override def preStart(): Unit ={        log.info("preStart() in FirstActor")        //通过context上下文创建Actor        child = context.actorOf(Props[MyActor], name = "myChild")      }      def receive = {        //向MyActor发送消息        case x => child ! x;log.info("received "+x)      }      //Hook方法，postStop()，Actor停止之后调用，用于完成初始化工作      override def postStop(): Unit = {        log.info("postStop() in FirstActor")      }    }

中分别对postStop、preStart方法进行了重写，在preStart方法中通过代码

 child = context.actorOf(Props[MyActor], name = "myChild")

对成员变量child进行初始化，然后在postStop方法中使用

 //通过context上下文停止MyActor的运行        context.stop(child)

停止MyActor的运行。在使用代码

//创建FirstActor对象val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
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创建FirstActor时，便会调用preStart方法完成MyActor的创建，因此首先会执行FirstActor中的preStart()方法

dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor

然后在创建MyActor时执行MyActor中定义的preStart方法

[INFO] [04/02/2016 17:04:49.608] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor/myChild] preStart() in MyActor
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在执行

//关闭ActorSystem，停止程序的运行    system.shutdown()

FirstActor作为MyActor的Supervisor，会先停止MyActor，再停止自身，因此先调用MyActor的postStop方法，再调用FirstActor的postStop方法。

（2） 成员变量self及成员方法sender方法的使用

整体代码如下：

  /* *Actor API:成员变量self及sender()方法的使用 */  object Example_05 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{      self!"message from self reference"      def receive = {        case "test" => log.info("received test");sender()!"message from MyActor"        case "message from self reference"=>log.info("message from self refrence")        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")    systemLog.info("准备向myactor发送消息")    //向myactor发送消息    myactor!"test"    myactor! 123    Thread.sleep(5000)    //关闭ActorSystem，停止程序的运行    system.shutdown()  }
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运行结果：

[INFO] [04/02/2016 18:40:37.805] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息[INFO] [04/02/2016 18:40:37.805] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received 123[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] message from self refrence[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received message from MyActor[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message

代码：

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

中使用

self!"message from self reference"
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向自身发送了一条消息，receive方法通过

        case "message from self reference"=>log.info("message from self refrence")

对这条消息进行处理。receive方法在处理

def receive = {        case "test" => log.info("received test");sender()!"message from MyActor"

“test”消息时，会调用

sender()!"message from MyActor"
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向sender（本例中为FirstActor）发送”message from MyActor”消息，FirstActor使用

 def receive = {        //向MyActor发送消息        case x => child ! x;log.info("received "+x)      }
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处理消息时又向MyActor回送该消息，因此最终的输出有两个unknown message，分别对应123和”message from MyActor”

[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message[INFO] [04/02/2016 18:40:37.806] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
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（3） unhandled方法的使用

unhandled方法用于处理没有被receive方法处理的消息，下面的代码给出的是当不重写unhandled方法时的代码

/**Actor API:unhandled方法*/object Example_06 extends App{  import akka.actor.Actor  import akka.actor.ActorSystem  import akka.actor.Props  class FirstActor extends Actor with ActorLogging{    def receive = {      //向MyActor发送消息      case "test" => log.info("received test")    }  }  val system = ActorSystem("MyActorSystem")  val systemLog=system.log  //创建FirstActor对象  val myactor = system.actorOf(Props[FirstActor], name = "firstActor")  systemLog.info("准备向myactor发送消息")  //向myactor发送消息  myactor!"test"  myactor! 123  Thread.sleep(5000)  //关闭ActorSystem，停止程序的运行  system.shutdown()}

代码输出：

[INFO] [04/02/2016 19:14:11.992] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息[INFO] [04/02/2016 19:14:11.992] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test
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不难看出，对于

 myactor! 123

发送的这条消息没有被处理，没有任何的处理逻辑。在实际开发过程中，可能会对不能被处理的消息增加一些应对逻辑，此时可以重写unhandled方法，代码如下：

/**Actor API:unhandled方法的使用*/object Example_06 extends App{  import akka.actor.Actor  import akka.actor.ActorSystem  import akka.actor.Props  class FirstActor extends Actor with ActorLogging{    def receive = {      //向MyActor发送消息      case "test" => log.info("received test")    }    //重写unhandled方法    override def unhandled(message: Any): Unit = {      log.info("unhandled message is {}",message)    }  }  val system = ActorSystem("MyActorSystem")  val systemLog=system.log  //创建FirstActor对象  val myactor = system.actorOf(Props[FirstActor], name = "firstActor")  systemLog.info("准备向myactor发送消息")  //向myactor发送消息  myactor!"test"  myactor! 123  Thread.sleep(5000)  //关闭ActorSystem，停止程序的运行  system.shutdown()}

代码输出结果：

[INFO] [04/02/2016 19:17:18.458] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息[INFO] [04/02/2016 19:17:18.458] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test[INFO] [04/02/2016 19:17:18.458] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] unhandled message is 123
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其它如preRestart等方法的使用将在Akka容错部分进行讲解。