FCM messaging with Java SDK: how to handle correctly and differentiate failures

Question

I'm using Firebase Cloud Messaging with Java SDK (com.google.firebase:firebase-admin v 5.9.0).

The only way to treat errors in Java code is to catch an ExecutionException:

Message message = buildMessage(token,payload);
try {
    String response = FirebaseMessaging.getInstance().sendAsync(message).get();
} catch (ExecutionException e) {
    LOGGER.error("ExecutionException Error pushing notif : ", e);
}
// Response is a message ID string.
LOGGER.info("Successfully sent message: " + response);

If I want to detect a deleted Token, I have to read the wrapped exception in ExecutionException (a FireBaseMessagingException), and test that message is "Requested entity was not found":

if(e.getCause().getMessage().equals("Requested entity was not found.") {
// token is deleted 
}

If I want to detect a network failure, I have to read the wrapped exception in ExecutionException (a FireBaseMessagingException), and test that message is "Error while calling FCM backend service":

if(e.getCause().getMessage().equals("Error while calling FCM backend service") {
// network problem, I have to retry 
}

Actions to make depend on this detection, which is very fragile. Is it possible to implement a more accurate determination of errors?

Answer 1

FirebaseMessagingException has an error code: https://firebase.google.com/docs/reference/admin/java/reference/com/google/firebase/messaging/FirebaseMessagingException.html#getErrorCode()

Possible error codes are defined here: https://firebase.google.com/docs/cloud-messaging/admin/errors