Remote EJB connectivity is Not Supported
JBoss Enterprise Web Platform does not support remote EJB connectivity. Further, other EJB support will be removed in versions of JBoss Enterprise Web Platform based on JBoss Application Server 6. If you require this functionality, use JBoss Enterprise Application Platform.
Session EJBs provide remote invocation services. They are clustered based on the client-side interceptor architecture. The client application for a clustered session bean is the same as the client for the non-clustered version of the session bean, except for some minor changes. No code change or re-compilation is needed on the client side. This chapter shows you how to configure clustered session beans in EJB 3.0 and EJB 2.x server applications respectively.
Clustering stateless session beans is the simplest case since no state is involved. Calls can be load balanced to any participating node (that is, any node that has this specific bean deployed) of the cluster.
To cluster a stateless session bean in EJB 3.0, simply annotate the bean class with the
@Clustered annotation. This annotation contains optional parameters for overriding both the load balance policy and partition to use.
public @interface Clustered
{
String partition() default "${jboss.partition.name:DefaultPartition}";
String loadBalancePolicy() default "LoadBalancePolicy";
}
partition- Specifies the name of the cluster the bean participates in. While the
@Clusteredannotation lets you override the default partition,DefaultPartition, for an individual bean, you can override this for all beans using thejboss.partition.namesystem property. loadBalancePolicy- Defines the name of a class implementing
org.jboss.ha.client.loadbalance.LoadBalancePolicy, indicating how the bean stub should balance calls made on the nodes of the cluster. The default value,LoadBalancePolicyis a special token indicating the default policy for the session bean type. For stateless session beans, the default policy isorg.jboss.ha.client.loadbalance.RoundRobin. You can override the default value using your own implementation, or choose one from the list of available policies:org.jboss.ha.client.loadbalance.RoundRobin- Starting with a random target, always favors the next available target in the list, ensuring maximum load balancing always occurs.
org.jboss.ha.client.loadbalance.RandomRobin- Randomly selects its target without any consideration to previously selected targets.
org.jboss.ha.client.loadbalance.aop.FirstAvailable- Once a target is chosen, always favors that same target; i.e. no further load balancing occurs. Useful in cases where "sticky session" behavior is desired, e.g. stateful session beans.
org.jboss.ha.client.loadbalance.aop.FirstAvailableIdenticalAllProxies- Similar to
FirstAvailable, except that the favored target is shared across all proxies.
The following is an example of a clustered EJB 3.0 stateless session bean implementation:
@Stateless
@Clustered
public class MyBean implements MySessionInt
{
public void test()
{
// Do something cool
}
}
Rather than using the
@Clustered annotation, you can also enable clustering for a session bean in jboss.xml:
<jboss>
<enterprise-beans>
<session>
<ejb-name>NonAnnotationStateful</ejb-name>
<clustered>true</clustered>
<cluster-config>
<partition-name>FooPartition</partition-name>
<load-balance-policy>org.jboss.ha.framework.interfaces.RandomRobin</load-balance-policy>
</cluster-config>
</session>
</enterprise-beans>
</jboss>
Note
The
<clustered>true</clustered> element is an alias for the <container-name>Clustered Stateless SessionBean</container-name> element in the conf/standardjboss.xml file.
In the bean configuration, only the
<clustered> element is necessary to indicate that the bean needs to support clustering features. The default values for the optional <cluster-config> elements match those of the corresponding properties from the @Clustered annotation.