Rings/J3D is a open source Java project of a 3d graphics raytracer by Mike Murray, see here. It seems no more up-to-date (0.4) and dropped since 2006 by its main developer.
For interested java developers, here is a Eclipse project including :
As a lot of classes are missing, some of them do not compile, mostly related to network processing. They are not essential, so you may simply delete them.
Download here (15Mo). See readme.txt inside.
Everything under GPL.
Mail here for help or informations.