After you start WebLogic, you will need to configure the startup and shutdown class in your web based admin console.  Log in, and select 'Deployments -> Startup & Shutdown' on your navigation pane.

Select 'Configure a new Startup Class', and fill out details of the j2ee service class as follows:

Now select 'Configure a new Shutdown Class', and fill out the details of the j2ee service class as follows:

If you click 'Startup & Shutdown classes' now, it should look like:

About the j2ee service class

This class is a simple one that takes in a single parameter, either start or stop.  This parameter tells the class how to behave.

start mode: In this mode, the class simply creates a new instance of org.jboss.cache.TreeCache, starts it as a service, and binds it in JNDI.

stop mode: In this mode, the class retrieves the TreeCache from JNDI and stops the caching service.

Note that the TreeCache takes care of discovering other TreeCaches in the cluster and replicating.  This is all configured in the jboss-cache configuration XML.