Make sure you have the following entry in weblogic.xml.
<container-descriptor>
<session-monitoring-enabled>true</session-monitoring-enabled>
</container-descriptor>
The above entry enable the respective MBean in weblogic. You can override it in Administration Console.
Now, open Administration Console. Go to the web application details. Click Monitoring tab. You will see number of active sessions, highest number of sessions coexisted at some point of time and total number of session created since the web application started.
