How to use akka.cluster.pubsub

@Override
public void publishToLocalRegion( String topic, Object message, ActorRef sender  ) {
  // send to local subscribers to topic
  mediator.tell( new DistributedPubSubMediator.Publish( topic, message ), sender );
}

public ReservationCacheActor() {
  // subscribe to the topic named "content"
  ActorRef mediator = DistributedPubSub.get(getContext().system()).mediator();
  mediator.tell(new DistributedPubSubMediator.Subscribe("content", getSelf()), getSelf());
}

private void initAkka() {
  logger.info("Initializing Akka");
  // Create one actor system with request actor for each region
  if ( StringUtils.isEmpty( currentRegion )) {
    throw new RuntimeException( "No value specified for: " + ActorSystemFig.CLUSTER_REGIONS_LOCAL );
  }
  if ( StringUtils.isEmpty( actorSystemFig.getRegionsList() )) {
    throw new RuntimeException( "No value specified for: " + ActorSystemFig.CLUSTER_REGIONS_LIST );
  }
  if ( StringUtils.isEmpty( actorSystemFig.getSeeds() )) {
    throw new RuntimeException( "No value specified for: " + ActorSystemFig.CLUSTER_SEEDS );
  }
  List regionList = Arrays.asList( actorSystemFig.getRegionsList().toLowerCase().split(",") );
  logger.info("Initializing Akka for hostname {} region {} regionList {} seeds {}",
    hostname, currentRegion, regionList, actorSystemFig.getSeeds() );
  Config config = createConfiguration();
  clusterSystem = createClusterSystem( config );
  // register our cluster listener
  clusterSystem.actorOf(Props.create(ClusterListener.class, getSeedsByRegion(), getCurrentRegion()),
    "clusterListener" );
  createClientActors( clusterSystem );
  mediator = DistributedPubSub.get( clusterSystem ).mediator();
}

  private void handleSubscribeAck(final DistributedPubSubMediator.SubscribeAck subscribeAck) {
    log.info("Successfully subscribed to distributed pub/sub on topic '{}'", subscribeAck.subscribe().topic());
  }
}

@Override
public void preStart() {
  pubSubMediator.tell(new DistributedPubSubMediator.Put(getSelf()), getSelf());
  pubSubMediator.tell(new DistributedPubSubMediator.Subscribe(BatchExecutionFinished.TYPE, ACTOR_NAME, getSelf()),
      getSelf());
}

  private static DistributedPubSubMediator.Send mapStreamTriggerCommand(
      final SudoStreamModifiedEntities sudoStreamModifiedEntities) {

    return new DistributedPubSubMediator.Send(ThingsMessagingConstants.THINGS_STREAM_PROVIDER_ACTOR_PATH,
        sudoStreamModifiedEntities, true);
  }
}

private void handleUnsubscribeAck(final DistributedPubSubMediator.UnsubscribeAck unsubscribeAck) {
  log.debug("Successfully unsubscribed from distributed pub/sub on topic <{}>.",
      unsubscribeAck.unsubscribe().topic());
}

  private void handleSubscribeAck(final SubscribeAck subscribeAck) {
    log.info("Successfully subscribed to distributed pub/sub on topic '{}'", subscribeAck.subscribe().topic());
  }
}

private static ActorRef getDistributedPubSubMediatorActor(final ActorSystem actorSystem) {
  return DistributedPubSub.get(actorSystem).mediator();
}

private BlockedNamespacesUpdater(final BlockedNamespaces blockedNamespaces, final ActorRef pubSubMediator) {
  this.blockedNamespaces = blockedNamespaces;
  // register self for pub-sub on restart
  pubSubMediator.tell(new Put(getSelf()), getSelf());
  // subscribe to namespace-blocking commands
  pubSubMediator.tell(new DistributedPubSubMediator.Subscribe(BlockNamespace.TYPE, getSelf()), getSelf());
  pubSubMediator.tell(new DistributedPubSubMediator.Subscribe(UnblockNamespace.TYPE, getSelf()), getSelf());
}

private static DistributedPubSubMediator.Send mapStreamTriggerCommand(
    final SudoStreamModifiedEntities sudoStreamModifiedEntities) {
  return new DistributedPubSubMediator.Send(PoliciesMessagingConstants.POLICIES_STREAM_PROVIDER_ACTOR_PATH, sudoStreamModifiedEntities,
      true);
}

private void handleUnsubscribeAck(final DistributedPubSubMediator.UnsubscribeAck unsubscribeAck) {
  log.debug("Successfully unsubscribed from distributed pub/sub on topic <{}>.",
      unsubscribeAck.unsubscribe().topic());
}

private void handleSubscribeAck(final DistributedPubSubMediator.SubscribeAck subscribeAck) {
  log.debug("Successfully subscribed to distributed pub/sub on topic <{}>.",
      subscribeAck.subscribe().topic());
}

private static ActorRef getDistributedPubSubMediatorActor(final ActorSystem actorSystem) {
  return DistributedPubSub.get(actorSystem).mediator();
}

  private static DistributedPubSubMediator.Send mapStreamTriggerCommand(
      final SudoStreamModifiedEntities sudoStreamModifiedEntities) {

    return new DistributedPubSubMediator.Send(ThingsMessagingConstants.THINGS_STREAM_PROVIDER_ACTOR_PATH,
        sudoStreamModifiedEntities, true);
  }
}

private void handleSubscribeAck(final DistributedPubSubMediator.SubscribeAck subscribeAck) {
  log.debug("Successfully subscribed to distributed pub/sub on topic <{}>.",
      subscribeAck.subscribe().topic());
}

private static DistributedPubSubMediator.Send mapStreamTriggerCommand(
    final SudoStreamModifiedEntities sudoStreamModifiedEntities) {
  return new DistributedPubSubMediator.Send(PoliciesMessagingConstants.POLICIES_STREAM_PROVIDER_ACTOR_PATH, sudoStreamModifiedEntities,
      true);
}

private void subscribeAck(final DistributedPubSubMediator.SubscribeAck subscribeAck) {
  log.debug("Successfully subscribed to distributed pub/sub on topic '{}'", subscribeAck.subscribe().topic());
}

private static DistributedPubSubMediator.Send wrapForPubSub(final Signal<?> signal) {
  return new DistributedPubSubMediator.Send(DISPATCHER_ACTOR_PATH, signal);
}

private void subscribeAck(final DistributedPubSubMediator.SubscribeAck subscribeAck) {
  log.debug("Successfully subscribed to distributed pub/sub on topic '{}'", subscribeAck.subscribe().topic());
}