jOTR is a Java framework that provides the base functionality for OTR (Off The Record) support. It is intended to be a java version of the c-based libotr, and be completely compatible with it. Sounds great but, there is no source code although the project is more than a year old.
Ian Goldberg, lead developer of the OTR development team, mentions an otr library for Java (java-otr) (here) that is in the workings. There is no source code or binaries, only a mentioning so I sent a follow up mail (here) with no reply, so we can't rely on this.
libjotr ibjotr is a Off-The-Record library in native java. It was developed for libkara but can also be used with other applications written in java. This seems to be the first and only existing implementation for OTR in Java. libjotr is working but it will be hard to use it with an other messenger than kara without modfying the API. It is also OTR v2 only. No support for Version 1. These information are confirmed by Markus, libjotr developer.