List<BufferedImage> boxFrames = makeTextboxAnimation(boxes); // create frames for GIF
final byte[] data = new byte[1];
Image image = null;
try (ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageOutputStream ios = ImageIO.createImageOutputStream(baos)) {
    ImageWriter writer = ImageIO.getImageWritersByFormatName("gif").next();
    ImageWriteParam param = writer.getDefaultWriteParam();
    IIOMetadata meta = writer.getDefaultImageMetadata(
            ImageTypeSpecifier.createFromBufferedImageType(boxFrames.get(0).getType()), param);
    String metaFormatName = meta.getNativeMetadataFormatName();
    IIOMetadataNode root = (IIOMetadataNode) meta.getAsTree(metaFormatName);
    IIOMetadataNode graphicsControl = getNode(root, "GraphicControlExtension");
    graphicsControl.setAttribute("disposalMethod", "none");
    graphicsControl.setAttribute("userInputFlag", "FALSE");
    graphicsControl.setAttribute("transparentColorFlag", "FALSE");
    graphicsControl.setAttribute("delayTime", "10");
    graphicsControl.setAttribute("transparentColorIndex", "0");
    IIOMetadataNode comments = getNode(root, "CommentExtensions");
    comments.setAttribute("CommentExtension", "Animated OneShot Textbox");
    IIOMetadataNode application = getNode(root, "ApplicationExtensions");
    IIOMetadataNode child = new IIOMetadataNode("ApplicationExtension");
    child.setAttribute("applicationID", "NETSCAPE");
    child.setAttribute("authenticationCode", "2.0");
    child.setUserObject(new byte[] { 0x1, (byte) (0 & 0xFF), (byte) ((0 >> 8) & 0xFF) });
    application.appendChild(child);
    meta.setFromTree(metaFormatName, root);
    writer.setOutput(ios);
    writer.prepareWriteSequence(null);
    for (int i = 0; i < boxFrames.size(); i++) {
        BufferedImage frame = boxFrames.get(i);
        writer.writeToSequence(new IIOImage(frame, null, meta), param);
    }
    writer.endWriteSequence();
    byte[] tmp = baos.toByteArray();
    System.arraycopy(tmp, 0, data, 0, tmp.length);
    image = Toolkit.getDefaultToolkit().createImage(data);
} catch (IOException e1) {
    e1.printStackTrace();
    JOptionPane.showMessageDialog(this, "An exception occured while generating the animation:\n" + e1,
            "Couldn't generate animation!", JOptionPane.ERROR_MESSAGE);
}