Usually, one calls into Oracle from an EJB running in JBoss, not the other way around.
In this scenario, if it is indeed what you want to do, JMS would be your best bet. Oracle has a JMS provider which you can leverage from the DB platform that can post messages to listeners in JBoss. You would have to consult your Oracle documentation (and your wallet) to make sure that this is a viable solution for you ;-)
As Peter suggests, this is not a typical use case.