Java Programming

I have a program that reads an image from inside a jar (buillt dynamically in code) using ImageIO.read(URL);

This works fine and I can read the image as many times as I like. However, if I rebuild the jar in code and try to read the image of the same name a second time the read returns null without throwing any Exceptions.

It's as if java has cached the stream to the original file even though I have created a new URL.

Any ideas anyone?