You cannot directly share data between two web applications. Instead, you will need a third component that handles the shared data and both of your apps will have to call into that third component. That third component could be, for example, a database, or a web app that exposes a web services interface.
I know Tomcat has a parameter in the context.xml called crossContext that when set to true you can get the request dispatcher for other applicatons on the same virtual host. Not sure if JBoss has a similar implementation but at least it provides a starting point..