Become/unbecome behavior of an actor

In some situations, we want our actor to change its behavior based on its state. This means that there are cases where an actor receives a message, and if its state changes or transitions, it changes the way further messages should be handled.

Thus, using become/unbecome, we can hot swap the actor functionality at runtime.

Getting ready

To step through this recipe, we need to import the Hello-Akka project in the IDE-like IntelliJ Idea. Prerequisites are the same as those in previous recipes.

How to do it...

1. Create a file named BecomeUnbecome.scala in package com.packt.chapter1.
2. Add the following imports to the top of the file:

        import akka.actor.{Props, ActorSystem, Actor} 

3. Define an actor which changes its behavior based on whether the state is true or false, as shown in the following code:

        class BecomeUnBecomeActor extends Actor { 
          def receive: Receive = { 
            case true => context.become(isStateTrue) 
            case false => context.become(isStateFalse) 
            case _ => println("don't know what you want to say !! ") 
          } 
          def isStateTrue: Receive  = { 
            case msg : String => println(s"$msg") 
            case false => context.become(isStateFalse) 
          } 
          def isStateFalse: Receive  = { 
            case msg : Int => println(s"$msg") 
            case true =>  context.become(isStateTrue) 
          } 
        } 

4. Create a test application, BecomeUnBecomeApp, as follows:

        object BecomeUnBecomeApp extends App { 
          val actorSystem = ActorSystem("HelloAkka") 
          val becomeUnBecome = 
           actorSystem.actorOf(Props[BecomeUnBecomeActor]) 
          becomeUnBecome ! true 
          becomeUnBecome ! "Hello how are you?" 
          becomeUnBecome ! false 
          becomeUnBecome ! 1100 
          becomeUnBecome ! true 
          becomeUnBecome ! "What do u do?" 
        } 

5. Run the application in an IDE like IntelliJ Idea or from the console; the output will be as follows:

      Hello how are you?
      1100
      What do u do?  

How it works...

In step two, we define an actor, which changes its state to handle string and integer values.

If the state is true, we set the behavior as context.become(isStateTrue), and it starts handling string messages. If the state is false, we set the behavior as context.become(isStateFalse), and it starts handling integer messages.

In step four, we create the actor and send it to see if the output matches the functionality.