Animated Gifからフレーム画像を抽出する

private static List<BufferedImage> loadFromStream(ImageInputStream imageStream) throws IOException {
  Iterable<ImageReader> it = () -> ImageIO.getImageReaders(imageStream);
  ImageReader reader = StreamSupport.stream(it.spliterator(), false)
      .filter(MainPanel::checkGifFormat)
      .findFirst()
      .orElseThrow(() -> new IOException("Can not read image format!"));
  reader.setInput(imageStream, false, false);
  List<BufferedImage> list = new ArrayList<>();
  for (int i = 0; i < reader.getNumImages(true); i++) {
    IIOImage frame = reader.readAll(i, null);
    list.add((BufferedImage) frame.getRenderedImage());
  }
  reader.dispose();
  return list;
}

private static boolean checkGifFormat(ImageReader reader) {
  String metaFormat = reader.getOriginatingProvider().getNativeImageMetadataFormatName();
  String name;
  try {
    name = reader.getFormatName();
  } catch (IOException ex) {
    name = "";
  }
  return "gif".equalsIgnoreCase(name) && "javax_imageio_gif_image_1.0".equals(metaFormat);
}