What is the correct way to get the messaging token for FCM in Android?

Good evening!

I am looking to add Firebase cloud messaging to my project (Android, Java). I have followed the documentation
https://firebase.google.com/docs/cloud-messaging/android/client#retrieve-the-current-registration-token
to a tee, but am still having issues retrieving the messaging token. Android studio claims Cannot resolve method 'getToken' in 'FirebaseMessaging' and will not compile. I assume I need to write a method getToken(), but can not find any documentation on what that method should do.

Here is my class, which extends FirebaseMessagingService as the documentation describes.

public class PushNotificationManager extends FirebaseMessagingService {

    public String MT;

    public PushNotificationManager() {
        FirebaseMessaging.getInstance().getToken()
                .addOnCompleteListener(new OnCompleteListener<String>() {
            @Override
            public void onComplete(@NonNull Task<String> task) {
                if (!task.isSuccessful()) {
                    System.out.println("Failed to get token");
                    return;
                }
                MT = task.getResult();

            }
        });
    }

    @Override
    public void onNewToken(String token) {
        super.onNewToken(token);
        MT =  token;
        System.out.println("Refreshed token: " + token);
    }
}

I also override onNewToken(), per the docs, but I never get a print to the logs.

Here is the service I added to the manifest:

        <service android:name=".PushNotificationManager">
            <intent-filter>
                <action android:name="com.google.firebase.MESSAGING_EVENT" />
            </intent-filter>
        </service>

There are a number of old stack overflow articles about this subject, but none have worked, most are older than a year, and use InstanceID() which is now depreciated.

Any suggestions? Thank you for your time!

UPDATE

Thanks to my conversation below with Doug, I have solved my issue. Firstly, I focused on onNewToken() in this class, and deleted my getToken() request in the constructor.

public class PushNotificationManager extends FirebaseMessagingService {

    public String MT;

    public PushNotificationManager() {

    }

    @Override
    public void onNewToken(String token) {
        super.onNewToken(token);
        MT =  token;
        System.out.println("Refreshed token: " + token);
    }
}

This, in combination with the updates to the manifest file, logs the messaging token on app start up After a complete reinstall. Now, to store the token in Firebase RTB, I need to access this after I initialize the database. So I added a method in my database class, which is called after the database is initialized. It looks like this:

    private void setMT()
    {
        FirebaseInstanceId.getInstance().getInstanceId()
                .addOnCompleteListener(new OnCompleteListener<InstanceIdResult>() {
                    @Override
                    public void onComplete(@NonNull Task<InstanceIdResult> task) {
                        if (!task.isSuccessful()) {
                            //Log.w(TAG, "getInstanceId failed", task.getException());
                            return;
                        }

                        // Get new Instance ID token
                        String MT = (String) task.getResult().getToken();
                        System.out.println("Messaging token: "+MT);
//Now I can save it to the RTB
                    }
                });
    }

And now its working! Thanks for the help, Doug!

If you are overriding onNewToken in a registered subclass of FirebaseMessagingService, then you don't need anything else to get a token. You either fetch it on demand with getToken, or you receive it via callback with onNewToken. There is little reason to do both (especially in the same class), unless you absolutely know you need to.

If you don't get a callback to onNewToken, then you probably didn't fully follow the instructions and add your subclass of FirebaseMessagingService as an Android service in your manifest.