Firebase push notifications with Eclipse Microprofile Rest Client

05 March 2020

Nowadays Push notifications is a must have feature for any trend application. Firebase Cloud Messaging (FCM) is a free (at least in this moment) cross-platform solution for messages and notifications for Android, iOS and Web applications.

firebase, push, microprofile, rest client

To enable push notification on client side you should create Firebase project and follow the manual or examples. From the server side perspective all you need to send push notification is:

Server key - will be created for your firebase project
Instance ID token - id of specific subscribed instance (instance destination id)

Firebase provides https://fcm.googleapis.com/fcm/send endpoint and very simple HTTP API like

{
    "to": "<Instance ID token>",
    "notification": {
      "title": "THIS IS MP REST CLIENT!",
      "body": "The quick brown fox jumps over the lazy dog."
      }
}

So, let's design simple Microprofile REST client to deal with above:

@Path("/")
@RegisterRestClient(configKey = "push-api")
public interface PushClientService {

    @POST
    @Path("/fcm/send")
    @Produces("application/json")
    @ClientHeaderParam(name = "Authorization", value = "{generateAuthHeader}")
    void send(PushMessage msg);

    default String generateAuthHeader() {
        return "key=" + ConfigProvider.getConfig().getValue("firebase.server_key", String.class);
    }
}

public class PushMessage {

    public String to;
    public PushNotification notification;

    public static class PushNotification {
        public String title;
        public String body;
    }
}

and application.properties

# firebase server key
firebase.server_key=<SERVER_KEY>
# rest client
push-api/mp-rest/url=https://fcm.googleapis.com/

Actually, this is it! Now you able to @Inject PushClientService and enjoy push notifications as well.

@Inject
@RestClient
PushClientService pushService;
...
pushService.send(message);

If you would like to test how it works from client side perspective, - feel free to use Test web application to generate instance ID token and check notifications delivery.

Described sample application source code with swagger-ui endpoint and firebase.server_key available on GitHub