To cluster stateful session beans in EJB 3.0, you need to tag the bean implementation class with the @Cluster annotation, just as we did with the EJB 3.0 stateless session bean earlier.

@Stateful
@Clustered
public class MyBean implements MySessionInt {
   
   private int state = 0;

   public void increment() {
      System.out.println("counter: " + (state++));
   }
}
            

JBoss Cache provides the session state replication service for EJB 3.0 stateful session beans. The related MBean service is defined in the ejb3-clustered-sfsbcache-service.xml file in the deploy directory. The contents of the file are as follows.

<server>
   <mbean code="org.jboss.ejb3.cache.tree.PassivationTreeCache"
       name="jboss.cache:service=EJB3SFSBClusteredCache">
      
        <attribute name="IsolationLevel">READ_UNCOMMITTED</attribute>
        <attribute name="CacheMode">REPL_SYNC</attribute>
        <attribute name="ClusterName">SFSB-Cache</attribute>
        <attribute name="ClusterConfig">
            ... ...
        </attribute>

        <!--  Number of milliseconds to wait until all responses for a
              synchronous call have been received.
        -->
        <attribute name="SyncReplTimeout">10000</attribute>

        <!--  Max number of milliseconds to wait for a lock acquisition -->
        <attribute name="LockAcquisitionTimeout">15000</attribute>

        <!--  Name of the eviction policy class. -->
        <attribute name="EvictionPolicyClass">
            org.jboss.ejb3.cache.tree.StatefulEvictionPolicy
        </attribute>

        <!--  Specific eviction policy configurations. This is LRU -->
        <attribute name="EvictionPolicyConfig">
            <config>
                <attribute name="wakeUpIntervalSeconds">1</attribute>
                <name>statefulClustered</name>
                <region name="/_default_">
                    <attribute name="maxNodes">1000000</attribute>
                    <attribute name="timeToIdleSeconds">300</attribute>
                </region>
            </config>
        </attribute>

        <attribute name="CacheLoaderFetchPersistentState">false</attribute>
        <attribute name="CacheLoaderFetchTransientState">true</attribute>
        <attribute name="FetchStateOnStartup">true</attribute>
        <attribute name="CacheLoaderClass">
            org.jboss.ejb3.cache.tree.StatefulCacheLoader
        </attribute>
        <attribute name="CacheLoaderConfig">
            location=statefulClustered
        </attribute>
   </mbean>
</server>
            

The configuration attributes in the PassivationTreeCache MBean are essentially the same as the attributes in the standard JBoss Cache TreeCache MBean discussed in Chapter 2, JBossCache and JGroups Services. Again, we omitted the JGroups configurations in the ClusterConfig attribute (see more in Section 2.1, “JGroups Configuration”).