I need to allow users to upload files and pictures.

Writing your own thumbnail generator is not very hard, either.

I would also recommend that you generate the thumbnails a single time, instead of wasting your processor time re-generating the thumbnails on each request. Pick a good file naming convention and use it to generate the thumbnails when the user first uploads their image.

In any case, the way to play with images is this:

1. Load the image form a file (or byte array) using java.awt.Toolkit.createImage
2. Create a new BufferedImage with the desired size
3. Get a Graphics object from the BufferedImage
4. Draw (and scale) your Image on to the Graphics object either with a method that scales your Image for you, or after calling Image.getScaledImage
5. Use a com.sun.image.codec.jpeg.JPEGImageEncoder to turn your BufferedImage into a JPEG file