It doesn’t look like there is much to do to port to java by looking at the js code but also not knowing how experienced your java coding is. Just try it and if you encounter obstacles, you can post the code and we can then see how to solve the possible issues.
Ok!
The godice sounds quite interesting and it would be surely fun to port it to java … but to be honest, I wouldn’t pay 100+ bucks for it and without one the testing of the port would be almost difficult.