For serial communication with java, I used JNI (Java Native Interface) to make available a shared library I wrote in C that provides access to the serial port.  Might be other ways, but I have this up and running so I stopped looking into that area.
If anyone is interested in my project, I've included some links below.

Date: Thu, 22 Mar 2007 12:39:39 +1200
Subject: [Gumstix-users] best serial port language to use


I am interested in using a gumstix device to communicate to some external hardware over a serial port. I see that Python and Java are being used - does anyone have any experience with java and serial ports on the gumstix.  a second question is about the object database - has anyone used this on a gumstix device? thanks, John

Your friends are close to you. Keep them that way.