Mine (notification) tells me in the logs when this occurs. 

-----Original Message-----
From: Godmar Back [mailto:god...@gmail.com] 
Sent: Thursday, April 22, 2010 9:48 PM
To: Tomcat Users List
Subject: Re: Q: how to obtain notification when a WebApp is unloaded/reloaded?

Following up on an earlier conversation about how to obtain notification when a 
WebApp is unloaded/reloaded [1], I was told that registering a 
ServletContextListener is the only possibility (that is, there is no runtime

However, registering a ServletContextListener doesn't work and leads to me 
being unable to start the web application.

To recap: I have an application with context reloadable=true. I continuously 
recompile this application during development. The application starts a worker 
thread I need to shut down when a newly compiled version of the application is 
loaded (that is, when new versions of the .class files show up in the 
WEB-INF/classes directory.

Right now, I'm getting messages that the listener class is missing (it isn't
- it's just a new .class file after recompilation.)

Apr 22, 2010 10:31:25 PM org.apache.catalina.loader.WebappClassLoader
SEVERE:     Resource
is missing
Apr 22, 2010 10:31:25 PM org.apache.catalina.core.StandardContext reload
INFO: Reloading this Context has started Apr 22, 2010 10:31:25 PM 
org.apache.catalina.core.StandardContext start
SEVERE: Error listenerStart
Apr 22, 2010 10:31:25 PM org.apache.catalina.core.StandardContext start
SEVERE: Context [/gbed] startup failed due to previous errors

My web.xml contains:


So - what is the correct way to register a listener that is executed when an 
application is reloaded due to a recompilation?

Does Tomcat get confused when the listener class itself is part of the 
to-be-reloaded web application?


 - Godmar

[1] See
and the messages in that thread.

---------- Forwarded message ----------
From: Godmar Back <god...@gmail.com>
Date: Wed, Apr 14, 2010 at 10:20 AM
Subject: Re: Q: how to obtain notification when a WebApp is unloaded/reloaded?
To: Tomcat Users List <users@tomcat.apache.org>

On Wed, Apr 14, 2010 at 10:12 AM, Pid <p...@pidster.com> wrote:

> > For instance, if you look at
> >
> http://java.sun.com/products/servlet/2.3/javadoc/javax/servlet/Servlet
> ContextListener.html
> > it says:
> >
> > "To recieve (sic) notification events, the implementation class must 
> > be configured in the deployment descriptor for the web application."
> Web applications are largely configured by the web.xml file in 
> app/WEB-INF.  Servlets, listeners etc are all configured in it.
Thank you for your confirmation.  I thought I was going nuts, after having 
waded through various *Facade classes, hoping to find an API method I could 
call at runtime.

I have added a ServletContextListener, but it is very much a solution I 
strongly dislike. The reason is that my application is layered on top of 
another application (ZK), and I don't really want to touch web.xml.
'web.xml' describes how ZK is configured to run inside Tomcat or another J2EE 
server. My applications runs on top of ZK, and having to go and made changes to 
the underlying deployment descriptor violates basic principles of layering.

It also creates a maintenance problem (unless an application can have multiple 
.xml files that are combined to form a deployment descriptor).
Whenever ZK is updated, a new version of web.xml will be installed, and I would 
then have to merge my <listener> declaration into the new file.

Just out of curiosity, what is the rationale for the (apparently deliberate) 
lack of an runtime API?

 - Godmar

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