本章主要內容：
1. !消息發送，Fire-and-Forget消息模型
2. ？消息發送，Send-And-Receive-Future消息模型

Akka提供了兩種消息模型：fire-and-forget和Send-And-Receive-Future。fire-and-forget是一種單向消息發送模型，指的是異步發送消息，通過異步發送消息且消息發送后可以立即返回，Akka中使用?方法進行fire-and-forget消息發送，如stringActor!”Creating Actors with implicit val context”，它的意思是當前發送方Aactor向stringActor發送字符串消息”Creating Actors with implicit val context”，發送完該消息后立即返回，而無需等待stringActor的返回，!還有個重載的方法tell；Send-And-Receive-Future指的是異步發送消息則是一種雙向消息發送模型，向目標Actor發送完消息后，然后返回一個Future作為后期可能的返回，當前發送方Actor將等待目標Actor的返回，Akka中使用?方法進行Send-And-Receive-Future消息的發送，它也同樣有一個重載的方法ask

1. !消息發送，Fire-and-Forget消息模型

/*** 消息處理：!(Fire-Forget)*/ object Example12 extends App{import akka.actor.Actorimport akka.actor.Propsimport akka.event.Loggingimport akka.actor.ActorSystem//定義幾種不同的消息case class Start(var msg:String)case class Run(var msg:String)case class Stop(var msg:String)class ExampleActor extends Actor {val other = context.actorOf(Props[OtherActor], "OtherActor")val log = Logging(context.system, this)def receive={//使用fire-and-forget消息模型向OtherActor發送消息，隱式地傳遞sendercase Start(msg) => other ! msg//使用fire-and-forget消息模型向OtherActor發送消息，直接調用tell方法，顯式指定sendercase Run(msg) => other.tell(msg, sender)}}class OtherActor extends Actor{val log = Logging(context.system, this)def receive ={case s:String=>log.info("received message:\n"+s)case _ ? log.info("received unknown message")}}//創建ActorSystem,ActorSystem為創建和查找Actor的入口//ActorSystem管理的Actor共享配置信息如分發器(dispatchers)、部署（deployments）等val system = ActorSystem("MessageProcessingSystem")//創建ContextActorval exampleActor = system.actorOf(Props[ExampleActor],name="ExampleActor")//使用fire-and-forget消息模型向exampleActor發送消息exampleActor!Run("Running")exampleActor!Start("Starting")//關閉ActorSystemsystem.shutdown() }

代碼運行結果如下：

[INFO] [03/20/2016 20:57:43.665] [MessageProcessingSystem-akka.actor.default-dispatcher-5] [akka://MessageProcessingSystem/user/ExampleActor/OtherActor] received message: Running [INFO] [03/20/2016 20:57:43.672] [MessageProcessingSystem-akka.actor.default-dispatcher-5] [akka://MessageProcessingSystem/user/ExampleActor/OtherActor] received message: Starting

在ExampleActor中，通過隱式變量context創建了OtherActor實例：val other = context.actorOf(Props[OtherActor], “OtherActor”)，在ExampleActor的receive方法中，處理兩種不同類型的消息例如：

//使用fire-and-forget消息模型向OtherActor發送消息，隱式地傳遞sendercase Start(msg) => other ! msg//使用fire-and-forget消息模型向OtherActor發送消息，直接調用tell方法，顯式指定sendercase Run(msg) => other.tell(msg, sender)

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處理Start類型的消息時，直接使用!進行消息發送，而處理Run類型的消息時，使用的是tell方法，可以看到使用tell方法需要顯式地指定其sender，而使用!進行消息發送則不需要，事實上!方法通過隱式值傳入需要的Sender，對比!與tell方法的定義便很容易理解

//!方法的定義 def !(message: Any)(implicit sender: ActorRef = Actor.noSender): Unit //tell方法的定義 final def tell(msg: Any, sender: ActorRef): Unit = this.!(msg)(sender)

可以看到，tell方法的實現依賴于!方法。如果在一個Actor當中使用!方法時，例如ExampleActor中使用的other ! msg向OtherActor發送消息，則sender隱式為ExampleActor，如果不是在Actor中使用則默認為Actor.noSender，即sender為null。

2. ？消息發送，Send-And-Receive-Future消息模型

理解了Fire-And-Forget消息模型后，接著對Send-And-Receive-Future消息模型進行介紹，下面的代碼給出了其使用示例。

/*** 消息處理：?(Send-And-Receive-Future)*/ object Example13 extends App{import akka.actor.Actorimport akka.actor.Propsimport akka.event.Loggingimport akka.actor.ActorSystemimport scala.concurrent.Futureimport akka.pattern.askimport akka.util.Timeoutimport scala.concurrent.duration._import akka.pattern.pipeimport scala.concurrent.ExecutionContext.Implicits.global//消息：個人基礎信息case class BasicInfo(id:Int,val name:String, age:Int)//消息：個人興趣信息case class InterestInfo(id:Int,val interest:String)//消息: 完整個人信息case class Person(basicInfo: BasicInfo,interestInfo: InterestInfo)//基礎信息對應Actorclass BasicInfoActor extends Actor{val log = Logging(context.system, this)def receive = {//處理送而來的用戶ID，然后將結果發送給sender（本例中對應CombineActor）case id:Int ?log.info("id="+id);sender!new BasicInfo(id,"John",19)case _ ? log.info("received unknown message")}}//興趣愛好對應Actorclass InterestInfoActor extends Actor{val log = Logging(context.system, this)def receive = {//處理發送而來的用戶ID，然后將結果發送給sender（本例中對應CombineActor）case id:Int ?log.info("id="+id);sender!new InterestInfo(id,"足球")case _ ? log.info("received unknown message")}}//Person完整信息對應Actorclass PersonActor extends Actor{val log = Logging(context.system, this)def receive = {case person: Person =>log.info("Person="+person)case _ ? log.info("received unknown message")}}class CombineActor extends Actor{implicit val timeout = Timeout(5 seconds)val basicInfoActor = context.actorOf(Props[BasicInfoActor],name="BasicInfoActor")val interestInfoActor = context.actorOf(Props[InterestInfoActor],name="InterestInfoActor")val personActor = context.actorOf(Props[PersonActor],name="PersonActor")def receive = {case id: Int =>val combineResult: Future[Person] =for {//向basicInfoActor發送Send-And-Receive-Future消息，mapTo方法將返回結果映射為BasicInfo類型basicInfo <- ask(basicInfoActor, id).mapTo[BasicInfo]//向interestInfoActor發送Send-And-Receive-Future消息，mapTo方法將返回結果映射為InterestInfo類型interestInfo <- ask(interestInfoActor, id).mapTo[InterestInfo]} yield Person(basicInfo, interestInfo)//將Future結果發送給PersonActorpipe(combineResult).to(personActor)}}val _system = ActorSystem("Send-And-Receive-Future")val combineActor = _system.actorOf(Props[CombineActor],name="CombineActor")combineActor ! 12345Thread.sleep(5000)_system.shutdown}

代碼運行結果如下：

[INFO] [03/20/2016 22:55:11.208] [Send-And-Receive-Future-akka.actor.default-dispatcher-3] [akka://Send-And-Receive-Future/user/CombineActor/BasicInfoActor] id=12345 [INFO] [03/20/2016 22:55:11.220] [Send-And-Receive-Future-akka.actor.default-dispatcher-2] [akka://Send-And-Receive-Future/user/CombineActor/InterestInfoActor] id=12345 [INFO] [03/20/2016 22:55:11.223] [Send-And-Receive-Future-akka.actor.default-dispatcher-4] [akka://Send-And-Receive-Future/user/CombineActor/PersonActor] Person=Person(BasicInfo(12345,John,19),InterestInfo(12345,足球))

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代碼中定義了3種類型的消息，分別是個人基礎信息case class BasicInfo(id:Int,val name:String, age:Int)、個人興趣信息case class InterestInfo(id:Int,val interest:String)以及完整個人信息case class Person(basicInfo: BasicInfo,interestInfo: InterestInfo)，然后為這3種類型的消息定義了相應的Actor即BasicInfoActor、InterestInfoActor和PersonActor，在CombineActor分別創建相應Actor的實例，receive方法中使用ask向BasicInfoActor、InterestInfoActor發送Send-And-Receive-Future模型消息，BasicInfoActor、InterestInfoActor中的receive方法接收到發送來的Int類型消息并分別使用!向CombineActor發送BasicInfo、InterestInfo消息，將結果保存在Future[Person]中，然后通過代碼pipe(combineResult).to(personActor)將結果發送給PersonActor。

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