public void getMp3Songs() {
    Uri uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
    String selection = MediaStore.Audio.Media.IS_MUSIC + "!=0";
    Cursor cursor = getContentResolver().query(uri, null, selection, null, null);
    if (cursor != null) {
        if (cursor.moveToFirst()) {
            do {
                String name = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.DISPLAY_NAME));
                String artist = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.ARTIST));
                String url = cursor.getString(cursor.getColumnIndex(MediaStore.Audio.Media.DATA));
                int songId = cursor.getColumnIndex(MediaStore.Audio.Media._ID);
                arrayList.add(new Songs(songId, name, url));


            } while (cursor.moveToNext());

        }

        cursor.close();
    }
}

private void initializePlayer(){
    player = ExoPlayerFactory.newSimpleInstance(new DefaultRenderersFactory(this), new DefaultTrackSelector()
                , new DefaultLoadControl());

    simpleExoPlayerView.setPlayer(player);
    player.setPlayWhenReady(playWhenReady);
    player.seekTo(currentWindow,playbackPosition);

    Uri uri = Uri.parse(url);
    MediaSource mediaSource = buildMediaSource(uri);
    player.prepare(mediaSource, true, false);
}

private MediaSource buildMediaSource(Uri uri) {
    return new ExtractorMediaSource(uri,
            new DefaultHttpDataSourceFactory("ua"),
            new DefaultExtractorsFactory(), null, null);
}