playlist

PlaylistParser.java

public class PlaylistParser
{
    /**
     * @param playlistContent a string representation of the playlist content
     * @return a list of string representation of a song
     */
    public List getFavoriteSongs(final String playlistContent) {
        final List<Optional<Song>> songs = parseSongs(playlistContent);

        return bestSongs(computeScores(songs));
    }

    private List<Song> bestSongs(Map<Song, Integer> scores) {
        return scores.entrySet().stream().parallel().
                sorted(scoreComparator()).limit(5).
                map(Entry::getKey).
                collect(toList());
    }

    private Map<Song, Integer> computeScores(List<Optional<Song>> songs) {
        return songs.stream().
                filter(Optional::isPresent).
                map(Optional::get).
                collect(groupingBy(identity(), summingInt(song -> 1)));
    }
}