Hmmm.... I guess that all depends on what you are trying to accomplish. A few things come to mind, although, they may be overkill on what you want to do:
First you have the Java Messenging system, where you can have java objects send messages to a "queue", and have another object pick those messages up.
You also have the EJB philosophy, where you can implement an object in an EJB, and call on that EJB from your different WAR applications.
The last option I can think of, would be to implement a Web Service of some kind.
Also, I'm curious on what you mean by "same session". It was my understanding that each application has it's "own session" and that the sessions aren't shareable.