class AlbumAssembler {

   // ...
   
   // Создаем новый альбом
   public void createAlbum(String id, AlbumDTO source) {
      Artist artist = Registry.findArtistNamed(source.getArtist());
      if (artist == null)
         throw new RuntimeException("No artist named " + source.getArtist());
      Album album = new Album(source.getTitle(), artist);
      createTracks(source.getTracks(), album);
      Registry.addAlbum(id, album);
   }
   
   private void createTracks(TrackDTO[] tracks, Album album) {
      for (int i = 0; i < tracks.length; i++) {
         Track newTrack = new Track(tracks[i].getTitle());
         album.addTrack(newTrack);
         createPerformers(newTrack, tracks[i].getPerformers());
      }
   }
   
   private void createPerformers(Track newTrack, String[] performerArray) {
      for (int i = 0; i < performerArray.length; i++) {
         Artist performer = Registry.findArtistNamed(performerArray[i]);
         if (performer == null)
            throw new RuntimeException("No artist named " + performerArray[i]);
         newTrack.addPerformer(performer);
      }
   }