Saving JFrame to Image File

Hi All,

I would like to save an (invisible) JFrame into an image file (jpeg).In other words, I only want to save the drawing to an image file without displaying it to the users.

I tried:

BufferedImage image = new BufferedImage(frame.getWidth(), frame.getHeight(),
BufferedImage.TYPE_INT_RGB);
Graphics2D graphics2D = image.createGraphics();
frame.panel.paint(graphics2D);
ImageIO.write(image,"png", new File("image.png"));

But this only works with a visible frame (frame.setVisible(true))

Any thoughts?
Thanks a lot.