Earlier quoted context omitted.
I'll have to take a look and see if my JetDirect 300X has new firmware. EDIT: Nope, it's a Javapocalypse for that particular device.
Oh that's too bad. The 620N I put in my printer was new-in-box so it came with the original Java based firmware. Yuck. The other reason to look for new firmware is that there were various security issues that were resolved. FWIW it looks like you may be able to use HP Web Jetadmin which is some sort of .net monstrosity.
I should probably hide it behind a Pi but it works, never breaks and I can't really complain.