How to check other user Session alive in Spring Framework

I have searched a lot on stackoverflow questions but I couldn't find the solution that fulfill my requirement; if any one known about reference that exactly match my requirement please comment otherwise answer it.

I am developing Enterprise application using Spring Framework in team, I have successfully integrate the "JMS" using ActiveMQ in application. In this application User A send message to User B if user B is online otherwise not!

My Question is that how to check that User B session is live or not before user A message send to User B

Thanks In advance

Yasir Shabbir