Akka官网demo：

//#full-example
package akka
import akka.actor.{ Actor, ActorLogging, ActorRef, ActorSystem, Props }
//#greeter-companion
//#greeter-messages
object Greeter {
 //#greeter-messages
 def props(message: String, printerActor: ActorRef): Props = Props(new Greeter(message, printerActor))
 //#greeter-messages
 final case class WhoToGreet(who: String)
 case object Greet
}
//#greeter-messages
//#greeter-companion
//#greeter-actor
class Greeter(message: String, printerActor: ActorRef) extends Actor {
 import Greeter._
 import Printer._
 var greeting = ""
 def receive = {
 case WhoToGreet(who) =>
 greeting = message + ", " + who
 case Greet =>
 //#greeter-send-message
 printerActor ! Greeting(greeting)
 //#greeter-send-message
 }
}
//#greeter-actor
//#printer-companion
//#printer-messages
object Printer {
 //#printer-messages
 def props: Props = Props[Printer]
 //#printer-messages
 final case class Greeting(greeting: String)
}
//#printer-messages
//#printer-companion
//#printer-actor
class Printer extends Actor with ActorLogging {
 import Printer._
 def receive = {
 case Greeting(greeting) =>
 log.info("Greeting received (from " + sender() + "): " + greeting)
 }
}
//#printer-actor
//#main-class
object AkkaQuickstart extends App {
 import Greeter._
 // Create the 'helloAkka' actor system
 val system: ActorSystem = ActorSystem("helloAkka")
 //#create-actors
 // Create the printer actor
 val printer: ActorRef = system.actorOf(Printer.props, "printerActor")
 // Create the 'greeter' actors
 val howdyGreeter: ActorRef =
 system.actorOf(Greeter.props("Howdy", printer), "howdyGreeter")
 val helloGreeter: ActorRef =
 system.actorOf(Greeter.props("Hello", printer), "helloGreeter")
 val goodDayGreeter: ActorRef =
 system.actorOf(Greeter.props("Good day", printer), "goodDayGreeter")
 //#create-actors
 //#main-send-messages
 howdyGreeter ! WhoToGreet("Akka")
 howdyGreeter ! Greet
 howdyGreeter ! WhoToGreet("Lightbend")
 howdyGreeter ! Greet
 helloGreeter ! WhoToGreet("Scala")
 helloGreeter ! Greet
 goodDayGreeter ! WhoToGreet("Play")
 goodDayGreeter ! Greet
 //#main-send-messages
}
//#main-class
//#full-example

看起来官方的demo挺眼花缭乱的，但是它是入门akka的demo，为了说明akka的工作机制已经写得相对明了了，由于akka也是基于scala语言实现的所以我选择scala语言的实现的例子，同时熟悉一下scala的用法。

首先这个类我们从akka官网下载之后，解压然后复制到我们的idea工具中，运行一下，这里可能会运行失败，有可能是pom文件引用的版本不对，例如我的scala SDK版本是scala-sdk-2.11.8，而pom中引用的akka是 akka-actor_2.12

<dependency>
 <groupId>com.typesafe.akka</groupId>
 <artifactId>akka-actor_2.12</artifactId>
 <version>2.5.18</version>
</dependency>

这里把2.12改为2.11重新运行就可以了。

运行结果如下：

[INFO] [11/22/2018 16:30:33.678] [helloAkka-akka.actor.default-dispatcher-5] [akka://helloAkka/user/printerActor] Greeting received (from Actor[akka://helloAkka/user/goodDayGreeter#1309545673]): Good day, Play
[INFO] [11/22/2018 16:30:33.678] [helloAkka-akka.actor.default-dispatcher-5] [akka://helloAkka/user/printerActor] Greeting received (from Actor[akka://helloAkka/user/helloGreeter#-1160926357]): Hello, Scala
[INFO] [11/22/2018 16:30:33.678] [helloAkka-akka.actor.default-dispatcher-5] [akka://helloAkka/user/printerActor] Greeting received (from Actor[akka://helloAkka/user/howdyGreeter#-1887433215]): Howdy, Akka
[INFO] [11/22/2018 16:30:33.678] [helloAkka-akka.actor.default-dispatcher-5] [akka://helloAkka/user/printerActor] Greeting received (from Actor[akka://helloAkka/user/howdyGreeter#-1887433215]): Howdy, Lightbend

那么实例代码到底做了什么事情呢？

1，main class创建了一个ActorSystem，等等，main class从何而来，我们来看：

object AkkaQuickstart extends App

这里继承了App，这个App是trait修饰的scala对象，trait的意思是特征在scala中相当于java中interface，但是它功能更加强大可以定义方法的实现。在App中正是定义了main方法，启动的时候就会找到这个main方法进行执行。

ActorSystem：刚才说创建了一个ActorSystem，它是一个容器里面装了一堆actor，是actor的运行空间。

2，创建了一个printer actor和三个greeter actor

//#create-actors
// Create the printer actor
val printer: ActorRef = system.actorOf(Printer.props, "printerActor")
// Create the 'greeter' actors
val howdyGreeter: ActorRef =
 system.actorOf(Greeter.props("Howdy", printer), "howdyGreeter")
val helloGreeter: ActorRef =
 system.actorOf(Greeter.props("Hello", printer), "helloGreeter")
val goodDayGreeter: ActorRef =
 system.actorOf(Greeter.props("Good day", printer), "goodDayGreeter")
//#create-actors

这里给出的是创建actor的方法，解释一下第一步有了ActorSystem，第二步就是用它来创建actor，有点类似spring容器初始化注入的java类，通过actorOf方法创建，这里注意一下这个props。

Props：它是一个配置类，用于指定创建actor的选项标志，相当于一个工厂类，生产actor同时给actor起个名字贴个标签。

我们注意到创建printer actor与greeter actor不太一样，这里的不一样是用了不同的创建actor的方法，其中：

val howdyGreeter: ActorRef =
 system.actorOf(Greeter.props("Howdy", printer), "howdyGreeter")

这里是为了将printer和要传递的信息通过构造器参数传给了正在创建的howdyGreeter actor，因为后续的调用需要用到printer的打印日志方法，可以看到Greeter的定义如下：

class Greeter(message: String, printerActor: ActorRef) extends Actor {
 import Greeter._
 import Printer._
 var greeting = ""
 def receive = {
 case WhoToGreet(who) =>
 greeting = message + ", " + who
 case Greet =>
 //#greeter-send-message
 printerActor ! Greeting(greeting)
 //#greeter-send-message
 }
}

它直接是带构造参数进行创建的。

3，开始发送消息，发送消息流程如下：

具体看一下代码：

howdyGreeter ! WhoToGreet("Akka")
howdyGreeter ! Greet

首先，！是个什么鬼？点进去看一下：

def !(message : scala.Any)(implicit sender : akka.actor.ActorRef = { /* compiled code */ }) : scala.Unit

可以看到是akka定义的一个方法，用于使用sender发送消息，也相当于调用方法，这里调用的是WhoToGreet("Akka")，在Greeter中定义了receive方法，接收sender的发送消息：

def receive = {
 case WhoToGreet(who) =>
 greeting = message + ", " + who
 case Greet =>
 //#greeter-send-message
 printerActor ! Greeting(greeting)
 //#greeter-send-message
}

这里收到了WhoToGreet，然后greeting= message +“,”+"Akka",message是什么？就是在创造actor的时候通过构造器传入的参数，因此组合成为：greeting= “Howdy”+“,”+"Akka".

接下来调用howdyGreeter ! Greet，内部则是通过传入的printer的actor进行打印日志，整个流程就是如上图显示的调用过程。