GREEN_BELT_AKKA.md

Green Belt Akka

This doucment will briefly introduce some important parts of Akka specific for the implementation of this kata.

The official Akka documentation is really good (if we may say so ourselves): Akka Docs

Please note that this document describes parts of Akka very briefly and we refer to the original documentation for an in-depth description of Akka.

Akka Essentials

Below is a brief introduction of some concepts you will need for this kata with some pointers to where you can read more.

Actor Systems

An actor system is, among other things, the context in which actors operate. You can have multiple actor systems within the same JVM.

See Actor Systems

Creating ActorSystems

val system = ActorSystem("MyActorSystem")

Working with Actors

See Actors

Creating actors

In the system context, called top level actors (to be used sparsely). This creates an actor under "/user/myActorName".

val myActor = system.actorOf(Props[MyActor], "myActorName")

In the actor context, called children (i.e. when you're inside an actor)

val myActor = context.actorOf(Props[MyActor], "myActorName")

Looking up actors

Look up an actor by name (complete path)

val myActor = system.actorFor("/user/myActorName")
val remoteActor = system.actorFor("akka://OtherActorSystem@host:port/user/otherActorName")

Sending messages

Fire and forget

myActor ! "A message"

As futures (has performance implications)

import akka.pattern.ask

val myFuture = myActor ? "A message"

Passing along the original sender

myActor.forward("Another message")

Receiving messages

class MyActor extends Actor {
  def receive = {
	case "A message" => println(""Received the message")
	case "Another message" => println("Received that other message") 
  }
}

Replying

class MyActor extends Actor { def receive = { case "A message" => sender ! "Got it" } }

**Supervising actors**

See [Fault Tolerance](http://doc.akka.io/docs/akka/2.1.2/scala/fault-tolerance.html)

override val supervisorStrategy = OneForOneStrategy() { case _ => Restart // Stop, ... }

### Misc Tasks


**Scheduling messages**

To schedule a message to be sent sometime in the future, once or repeatedly use the scheduler.

See [Scheduler](http://doc.akka.io/docs/akka/2.1.2/scala/scheduler.html)

//Use the system's default dispatcher as ExecutionContext import system.dispatcher system.scheduler.schedule(2 seconds, 2 seconds, actor, "every other second message")

**Retrieving properties**

As you can see in the code there are some properties predefined in the ``application.conf`` file. To retrieve these properties, in the context of an actor, you can use the following:

context.system.settings.config.getString("...")