No example for client subscriptions provided

[FelixGaebler]

Could you please provide an example how to implement subscriptions for java clients?

[FelixGaebler]

@kobylynskyi is it even possbible?
Sorry for opening an issue then... didnt know about discussions so far.

[kobylynskyi]

I know there are multiple usages of this plugin for writing a server-side code related to subscriptions. But haven't seen a client-side code written in Java yet.

[FelixGaebler]

Challange accepted 😎

I got an modular application with multiple components. The main component is providing the graphql endpoint, the module contains services which call the generated client classes (so it can be easily changed) and other components call the modules services to access the data.

[FelixGaebler]

Easy, but working concept by using Java-WebSocket libary:

@Log4j2
public class SubscriptionClient extends WebSocketClient {

    private final Map<Integer, Subscription> subscriptionMap;

    public SubscriptionClient(URI serverURI) {
        super(serverURI);
        this.subscriptionMap = new HashMap<>();
    }

    @Override
    public void onOpen(ServerHandshake handshake) {
        JsonObject init = new JsonObject();
        init.addProperty("type", "connection_init");
        init.add("payload", new JsonObject());
        System.out.println(init.toString());

        send(init.toString());
    }

    @Override
    public void onMessage(String message) {
        System.out.println(message);
        JsonObject object = JsonParser.parseString(message).getAsJsonObject();
        String type = object.get("type").getAsString();

        if(!type.equals("data")) {
            return;
        }

        JsonObject data = object.get("payload").getAsJsonObject().get("data").getAsJsonObject();
        Subscription subscription = subscriptionMap.get(object.get("id").getAsInt());
        subscription.notify(data);
    }

    @Override
    public void onClose(int code, String reason, boolean remote) {
        subscriptionMap.clear();
        log.info("Socket connection closed {}with code {}: \"{}\"", code, reason, remote ? "by remote " : "");
    }

    @Override
    public void onError(Exception exception) {
        subscriptionMap.clear();
        log.error("Socket connection failed:", exception);
    }

    public Subscription start(String query) {
        Subscription subscription = Subscription.builder()
                .id(subscriptionMap.size() + 1)
                .build();

        JsonObject payload = new JsonObject();
        payload.add("variables", new JsonObject());
        payload.add("extensions", new JsonObject());
        payload.add("operationName", null);
        payload.addProperty("query", query);

        JsonObject start = new JsonObject();
        start.addProperty("id", subscription.getId());
        start.addProperty("type", "start");
        start.add("payload", payload);

        subscriptionMap.put(subscription.getId(), subscription);

        System.out.println(start.toString());
        send(start.toString());
        return subscription;
    }

    public void stop(Subscription subscription) {
        JsonObject stop = new JsonObject();
        stop.addProperty("id", subscription.getId());
        stop.addProperty("type", "stop");

        send(stop.toString());
    }

}

SubscriptionClient client = new SubscriptionClient(new URI("ws://localhost:8080/graphql"));
            client.connectBlocking();
            Subscription subscription = client.start("subscription {  subscribeSigns {    object {      id      name      frames {        line0        line1        line2        line3      }    }  }}");
            subscription.getObservable().subscribe(System.out::println);

@Data
@Builder
@AllArgsConstructor
public class Subscription {

    private int id;

    private PublishSubject<JsonObject> provider;

    private Observable<JsonObject> observable;

    public Subscription() {
        provider = PublishSubject.create();
        Flowable<JsonObject> publisher = provider.toFlowable(BackpressureStrategy.BUFFER);
        observable = publisher.toObservable();
    }

    public void notify(JsonObject object) {
        provider.onNext(object);
    }

}

I will try to create a PR with the knowledge I got

[kobylynskyi]

Awesome! Good job, man! 🚀

[pell-je]

Java-WebSocket libary

Can you add the imports to show what exact classes this example shows?