androidApp/app/src/main/java/com/localtransfer/TransferService.java

package com.localtransfer;

import android.app.Notification;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;

import androidx.core.app.NotificationCompat;

public class TransferService extends Service {

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {

        Intent notificationIntent = new Intent(this, MainActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this,
                0, notificationIntent, 0);

        Notification notification = new NotificationCompat.Builder(this, "CHANNEL_ID")
                .setContentIntent(pendingIntent)
                .build();

        startForeground(Transfer.NOTIF_SERVICE, notification);

        //do heavy work on a background thread
        //stopSelf();

        return START_NOT_STICKY;
    }

    @Override
    public IBinder onBind(Intent intent) {
        // TODO: Return the communication channel to the service.
        throw new UnsupportedOperationException("Not yet implemented");
    }
}