20.4. Stateful Session Bean in EJB 2.x
Clustering stateful session beans is more complex than clustering their stateless counterparts since JBoss needs to manage the state information. The state of all stateful session beans are replicated and synchronized across the cluster each time the state of a bean changes. The JBoss Enterprise Application Platform uses the
HASessionStateService bean to manage distributed session states for clustered EJB 2.x stateful session beans. In this section, we cover both the session bean configuration and the HASessionStateService bean configuration.
20.4.1. The EJB application configuration
In the EJB application, you need to modify the
jboss.xml descriptor file for each stateful session bean and add the <clustered> tag.
<jboss>
<enterprise-beans>
<session>
<ejb-name>nextgen.StatefulSession</ejb-name>
<jndi-name>nextgen.StatefulSession</jndi-name>
<clustered>True</clustered>
<cluster-config>
<partition-name>DefaultPartition</partition-nam>
<home-load-balance-policy>org.jboss.ha.framework.interfaces.RoundRobin</home-load-balance-policy>
<bean-load-balance-policy>org.jboss.ha.framework.interfaces.FirstAvailable</bean-load-balance-policy>
<session-state-manager-jndi-name>/HASessionState/Default</session-state-manager-jndi-name>
</cluster-config>
</session>
</enterprise-beans>
</jboss>
In the bean configuration, only the
<clustered> tag is mandatory to indicate that the bean works in a cluster. The <cluster-config> element is optional and its default attribute values are indicated in the sample configuration above.
The
<session-state-manager-jndi-name> tag is used to give the JNDI name of the HASessionStateService to be used by this bean.
The description of the remaining tags is identical to the one for stateless session bean. Actions on the clustered stateful session bean's home interface are by default load-balanced, round-robin. Once the bean's remote stub is available to the client, calls will not be load-balanced round-robin any more and will stay "sticky" to the first node in the list.
