This example is using Apache FOP and the TTF font Free 3 of 9 from http://www.squaregear.net/fonts/free3of9.shtml
Further documentation for Code 39 and example PDF URL can be found here:
The class org.apache.fop.fonts.apps.TTFReader was used to generate the included TrueType font metrics file. This can be done in a batch run via a script of with the shown Java code:
String[] arguments = new String[] { "/PATH_TO/free3of9.ttf", "/PATH_TO/free3of9.xml" };
TTFReader.main(arguments);