How can i check if an Akka actor exists (akka 2.2)?

Question

I have a java object which is not an actor which selects actors from an actor system with actorSelection(Path)). It is possible, that the selected actor does not exist in the system. In the Java Api ask() does not exist for ActorSelection, so I can not send and Identify message to the actor selection and use the sender of the response. I tried to solve the problem by sending the message to the actor anyway via the actor selection and then reacting to the deadletter. But I don't get any deadletters. How can I check with the ActorSelection if the actor is alive or does not exist? ``` ActorSystem system = ActorSystem.create("test"); //create test actor system.actorOf(Props.create(TestActor.class), "testActor"); //add dead letter listener to the system ActorRef eventBusActor = asys.actorOf(Props.create(EventBusActor.class), "eventbusactor"); system.eventStream().subscribe(eventBusActor, DeadLetter.class); //This works. The test actor receives the message ActorSelection a1 = asys.actorSele…

Accepted Answer

It looks like Akka left off support for `ActorSelection` on the java api for `ask`. I played with the code a little and I found something that works though. See if this code works for you:

```
import java.util.concurrent.TimeUnit;

import scala.concurrent.Await;
import scala.concurrent.Future;

import akka.actor.ActorIdentity;
import akka.actor.ActorRef;
import akka.actor.ActorSelection;
import akka.actor.ActorSystem;
import akka.actor.Identify;
import akka.actor.Props;
import akka.pattern.AskableActorSelection;
import akka.util.Timeout;

public class AskTest {

public static void main(String[] args) throws Exception{
    ActorSystem sys = ActorSystem.apply("test");
    sys.actorOf(Props.create(TestActor.class), "mytest");

ActorSelection sel = sys.actorSelection("/user/mytest");

Timeout t = new Timeout(5, TimeUnit.SECONDS);
    AskableActorSelection asker = new AskableActorSelection(sel);
    Future<Object> fut = asker.ask(new Identify(1), t);
    ActorIdentity ident = (ActorIdentity)Await.result(fut, t.duration());
    ActorRef ref = ident.getRef();
    System.out.println(ref == null);
  }
}
```

I just looked at how the scala ask support worked and hooked into it via java. This worked for me; I'm hoping it works for you.

How can i check if an Akka actor exists (akka 2.2)?

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