I'm a little confused at the moment.

My back story in short, is that I'm trying to set up a Minecraft server on an Ubuntu server I've recently set up, obviously to do this I needed Java, but after googling for a short while I wasn't entirely sure whether it is possible (or legal?) to do so in Ubuntu 12.04 due to licensing type issues - so I installed open JDK instead which appears not to work properly with the Minecraft server software (I half expected this)

I'm now considering uninstalling open JDK and instead trying to get proper Java on there instead, my question is, is this possible? Is it Legal? And if so how do I go about doing it? Because I'm finding it very difficult to find any instructions on how to do so for 12.04 . . .