Java's serial port support has a checkered history, with Sun not putting a lot of effort into the javax.comm library. Because of that, there is a community effort (RXTX) that is more robust. However, both libraries are difficult to install in end users' systems.


If you really want an all-Java solution, see: http://www.awce.com/gp3java.htm -- the update at the end shows how to use RXTX 2.1 and the earlier instructions will work with the Sun library (if you can find it for your platform) and RXTX 2.0 (if it actually works on your platform).


One other way to go is simply compile the simple GP3 library code into a DLL or .SO and use JNI to access it. This is probably the easiest way if you think you'll need to install into end user machines. The downside is you need a library built for each target platform.


You may also be interested in another Java serial port implementation that uses JNA at http://www.sparetimelabs.com/purejavacomm/purejavacomm.php.