Using Actors to send data to websockets

[Anmol Singh Jaggi]

I have been experimenting with Akka websockets and was able to send some static data to a websocket using the following code:

    import java.io.BufferedReader;
    import java.io.InputStreamReader;
    import java.util.concurrent.CompletionStage;
    import java.util.concurrent.TimeUnit;


    import akka.NotUsed;
    import akka.actor.ActorSystem;
    import akka.http.javadsl.ConnectHttp;
    import akka.http.javadsl.Http;
    import akka.http.javadsl.ServerBinding;
    import akka.http.javadsl.model.HttpRequest;
    import akka.http.javadsl.model.HttpResponse;
    import akka.http.javadsl.model.ws.Message;
    import akka.http.javadsl.model.ws.WebSocket;
    import akka.japi.Function;
    import akka.stream.ActorMaterializer;
    import akka.stream.Materializer;
    import akka.stream.javadsl.Flow;
    import akka.stream.javadsl.Sink;
    import akka.stream.javadsl.Source;


    public class Server {


      public static HttpResponse handleRequest(HttpRequest request) {
        System.out.println("Handling request to " + request.getUri());
        if (request.getUri().path().equals("/greeter")) {
          final Flow<Message, Message, NotUsed> greeterFlow = greeterHello();
          return WebSocket.handleWebSocketRequestWith(request, greeterFlow);
        } else {
          return HttpResponse.create().withStatus(404);
        }
      }


      public static void main(String[] args) throws Exception {
        ActorSystem system = ActorSystem.create();


        try {
          final Materializer materializer = ActorMaterializer.create(system);


          final Function<HttpRequest, HttpResponse> handler = request -> handleRequest(request);
          CompletionStage<ServerBinding> serverBindingFuture = Http.get(system).bindAndHandleSync(handler,
              ConnectHttp.toHost("localhost", 8080), materializer);


          // will throw if binding fails
          serverBindingFuture.toCompletableFuture().get(1, TimeUnit.SECONDS);
          System.out.println("Press ENTER to stop.");
          new BufferedReader(new InputStreamReader(System.in)).readLine();
        } finally {
          system.terminate();
        }
      }


      public static Flow<Message, Message, NotUsed> greeterHello() {
        return Flow.fromSinkAndSource(Sink.ignore(),
            Source.single(new akka.http.scaladsl.model.ws.TextMessage.Strict("Hello!")));
      }
    }

I now want to send some data to a websocket from an Actor, something like this:  

    import akka.actor.ActorRef;
    import akka.actor.UntypedActor;


    public class PushActor extends UntypedActor {
      @Override
      public void onReceive(Object message) {
        if (message instanceof String) {
          String statusChangeMessage = (String) message;
          // How to push this message to a socket ??
        } else {
          System.out.println(String.format("'%s':\nReceived unknown message '%s'!", selfActorPath, message));
        }
      }
     
    }

I am unable to find any example of how to do this online.

Could somebody please guide me on this?

[Rob Crawford]

Have you read this:

https://doc.akka.io/docs/akka-http/current/java/http/server-side/websocket-support.html

[Anmol Singh Jaggi]

Yes, but it wasn't very helpful.

[Mahesh Venugopal]

Hi Anmol,

I am currently looking for an answer to the exact same question that you posted here. I still haven't been able to find an answer to this. Had you been successful in finding an answer to this. Any help is greatly appreciated.