How to determine if URL is an image?

Question

I would like to check if URL given by user is image (jpg, png, gif). First idea: check only file extension in URL. Second idea: get this resource from server (by http get) and load into some Java picture library to get info if is it image (seriously disadvantage: slow). Or maybe yet another solution?

Answer 1

You should use HTTP HEAD, not a full GET. This should include the Content-Type as known by the server. You could of course test the extension first, and only do the expensive/slow HTTP roundtrip if it's inconclusive.