[jboss-dev-forums] [Design of Clustering on JBoss] - Re: Removing SFSB in HttpSessionListener

[bstansberry@jboss.com]

I decided to skip doing the aforementioned matrix of what's rational and not rational. The behavior an end user would want depends on what they do in their listener.  So, I've focused on creating an API for a pluggable policy where users can provide an implementation that tells the clustered session manager exactly what notifications to emit.  Class name of the policy impl to use would be specified in jboss-web.xml. For now we'd ship two standard impls, one of which provides the existing behavior, one of which suppresses HttpSessionListener and HttpSessionAttributeListener notifications when a session is expired due to undeploy.

To have a look at what I've done, see https://svn.jboss.org/repos/jbossas/branches/Branch_4_2/tomcat/src/main/org/jboss/web/tomcat/service/session/notification/ClusteredSessionNotificationPolicy.java and the other classes in the same package.

Basically, when an event occurs, before invoking on listeners we ask the policy if invoking on them is allowed for the given event.  We pass as params an enum describing the type of event, a data object describing the calling node's relationship to the session (e.g. is it active on this node, or are we just providing backup) and a boolean indicating whether the event is due to locally originated activity (as opposed to activity originating on another node.)

Note the class javadoc for ClusteredSessionNotificationPolicy where I emphasize that the container is not necessarily capable of supporting all the invocations that the policy might allow. This is critical as it allows me to provide today a policy API where users can state what they allow, without having at the same time to provide support for notifications not mandated by the servlet spec.  For example, we currently don't issue HttpSessionListener.sessionCreated() notifications when a session is created on another node.  As more non- spec-mandated notifications are supported, existing policy impls can appropriately allow/disallow the new notifications.

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