de.rkjava.serial.j3964r-package:
For direct data exchange in form of a byte array via serial interface with 3964R protocol
It uses the Communication API 2.0 from Sun, which you must have installed. E.g. for Windows:

win32com.dll to "$JAVA_HOME\bin"
comm.jar to "$JAVA_HOME\lib\ext"
javax.comm.properties to "$JAVA_HOME\lib"
($JAVA_HOME is somthing like "C:\Program Files\java\jre" or "/usr/lib/java/jre")

Sun provides the Communication API 2.0 for Windows and Solaris. For Linux there is a backend to the Solaris-Communication-API: www.rxtx.org. (I got the best experience with version rxtx-1.4.16pre2)