Ok, nobody seems interested in it but I'll post my working solution.
//'WordnetPOS' is an instance of the class POS defined in JWNL. It indicates the part of
//speech tag. token
JWNL.initialize(new FileInputStream("path/file_properties.xml"));
Dictionary wordnet = Dictionary.getInstance();
IndexWord token = wordnet.lookupIndexWord(WordnetPos, word); //word is a string
Synset[] senses = token.getSenses();
String Dom = new String();
for (int i = 0; i < senses.length; i++) {
String domSet = new String();
try {
//CATEGORY is the pointer type of the synset containing the domains
Pointer[] pointerArr = senses[i].getPointers(PointerType.CATEGORY);
for (Pointer pointer : pointerArr) {
Synset syn = pointer.getTargetSynset();
Word[] words = syn.getWords();
for (Word word : words) {
domaSet = domaSet + word.getLemma().trim().toLowerCase() + " ";
}
}
catch (NullPointerException e) {
}
Dom = Dom + domSet;
}