RedComm
RedComm is a Java library simplifying communication with a serial port
...RxTx is licensed under the LGPL 2.1 (http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html). RedComm also provides facilities for event based serial communication with the help of threading in order to non-block ie. the gui thread of the corresponding application.
RedComm is ideally suited for education e.g at schools.