strutsのtokenって絶対ユニークなの？
↓こんなことやっているけど？
byte id[] = session.getId().getBytes();
long current = System.currentTimeMillis();
if(current == previous)
current++;
previous = current;
byte now[] = (new Long(current)).toString().getBytes();
MessageDigest md = MessageDigest.getInstance("MD5");
md.update(id);
md.update(now);
return toHex(md.digest());