I copied the mp3 (kalimba.mp3) file into the raw folder in the res folder. But when the notification is triggered it produces the default sound.
You should replace this line:
notification.sound = Uri.parse("android.resource://com.example.serviceproject/" + R.raw.kalimba);
with this:
notification.setSound(Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE + "://" + getPackageName() + "/raw/kalimba"));
or in some cases:
notification.sound = Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE + "://" + getPackageName() + "/raw/kalimba");