Listener configure in DD

[gunjan deogam]

Please can any one clear me which listener are configure in DD and which are not?

[Frits Walraven]

Hi Gunjan,

In the web.xml:
ServletRequestListener
ServletRequestAttributeListener
HttpSessionListener
HttpSessionAttributeListener
ServletContextListener
ServletContextAttributeListener

and not in the web.xml
HttpSessionBindingListener
HttpSessionActivationListener

Regards,
Frits

[Michael Angstadt]

HttpSessionActivationListener is also configurable in the DD. You can configure it in the DD if you want to listen for when a session migrates to another VM. It can also be implemented by a session attribute class to prepare the attribute for the migration.

[Frits Walraven]

Hi Michael,

I don't think that is correct. According to the book of Sun Certified Web Component Developer Study Guide (by David Bridgewater) it is not like that:

Chapter 4:
Now we move on to two other session-related listeners which are different in character
to the listeners we have previously encountered, whether on session, request, or
context. These listeners are:
HttpSessionBindingListener
HttpSessionActivationListener
Classes implementing these listener interfaces are not declared in the deployment
descriptor. They become known to the web container through a different mechanism
entirely.

I checked the servlet 2.4 specs and it also confirms this

SRV.15.1.8 HttpSessionActivationListener
Objects that are bound to a session may listen to container events notifying them
that sessions will be passivated and that session will be activated. A container that
migrates session between VMs or persists sessions is required to notify all
attributes bound to sessions implementing HttpSessionActivationListener.

because they don't mention the phrase:

To receive notification events, the implementation
class must be configured in the deployment descriptor for the web application

or did I miss something?
Regards,
Frits

[Michael Angstadt]

Hi Frits,

I'm reading the Head First Servlets and JSP book and it says that it can go both ways. It says that it's used when

You want to know when a session attribute has been added, removed, or replaced (p.182).

and also when

You want to know when a session moves from one VM to another (p.264).

In an exercise (p.264), it asks the reader to mark whether the listener is used on an attribute class or defined in the DD and HttpSessionActivationListener has checkmarks next to both. But I've never written a distributed Java web app, so I don't know for sure.

[Christophe Verré]

Check this FAQ.

[gunjan deogam]

Thanks all of you. But I read that HttpSessionActivationListener configure in DD.

[Christophe Verré]

gunjan deogam wrote:Thanks all of you. But I read that HttpSessionActivationListener configure in DD.

Where ?

[Michael Angstadt]

The FAQ that Christophe referred to says that the Head First Servlets and JSP book has an error concerning this, so this is probably what I saw.