Hi, I have a similar enquiry as the original poster (In my case for Linux).
I do of course note that the API is just a specification but having taken advice on Googling for an implementation. The following text seems to be a common theme.
"Because Linux is a form of Unix, the authors of RXTX and JCL have wisely decided to reuse sun's solaris (unix) comm library. At this point, you must download and install this library: http://java.sun.com/products/javacomm/ "
So it would seem that a crucial step in working with serial ports is currently being blocked by Oracle no longer allowing access to the old library?
Looks like you can download it here now: [http://www.oracle.com/technetwork/java/javasebusiness/downloads/java-archive-downloads-misc-419423.html|http://www.oracle.com/technetwork/java/javasebusiness/downloads/java-archive-downloads-misc-419423.html]