HERE.OLP : How can I "Subscribe to Notifications" to a catalog?

Question

I am trying to subscribe to a catalog for notification. But cannot find symbol "thenAppy". Please help.

// subscription to notifications
CompletionStage<NotificationSubscriptionControl> controlStage =
    queryApi.subscribeToNotifications(consumerSettings)
        .thenApply(subscription -> {
            subscription
                .notifications()
                .runWith(Sink.foreach(notification ->
                    // this callback is called each time a new batch publication happens in catalog
                    System.out.printf("catalog %s has a new version %d\n", catalogHrn, notification.getCatalogVersion())
                ), myMaterializer);
            return subscription.subscriptionControl();
        });

[ERROR] COMPILATION ERROR : [INFO] ------------------------------------------------------------- [ERROR] Main.java:[41,25] cannot find symbol symbol: method thenApply((subscript...; }) location: interface org.apache.flink.streaming.api.functions.source.SourceFunction [ERROR] Main.java:[44,65] package akka.stream.javadsl does not exist [ERROR] Main.java:[47,40] cannot find symbol symbol: variable myMaterializer

Answer 1

Based on your compilation error, it appears you're trying to subscribe to a notification within a Flink app. The Flink data client queryApi returns a SourceFunction, not a CompletionStage. You can use it like so:

StreamExecutionEnvironment
    .getExecutionEnvironment()
    .addSource(
        query.subscribeToNotifications(
            new NotificationConsumerSettings(
                "my-notification-consumer-group-1"
            )
        )
    )
    .addSink(
        notification - > System.out.printf(
            "catalog %s has a new version %d\n",
            STREAMING_INPUT_CATALOG_HRN,
            notification
            .getCatalogVersion()
        )
    );

Answer 2

If subscribeToNotifications is a blocking function then you could wrap it in completedFuture method of CompletableFuture.

CompletionStage<NotificationSubscriptionControl> controlStage =
        CompletableFuture.completedFuture(queryApi.subscribeToNotifications(consumerSettings))
            .thenApply(
                subscription -> {
                  subscription
                      .notifications()
                      .runWith(
                          Sink.foreach(
                              notification ->
                                  // this callback is called each time a new batch publication
                                  // happens in catalog
                                  System.out.printf(
                                      "catalog %s has a new version %d\n",
                                      catalogHrn, notification.getCatalogVersion())),
                          myMaterializer);
                  return subscription.subscriptionControl();
                });