On 23/04/2010 03:48, Godmar Back wrote:
> 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
> API.)
> 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
> modified
> SEVERE:     Resource
> '/WEB-INF/classes/org/libx/editionbuilder/GCHelper$ShutdownListener.class'
> is missing
> Apr 22, 2010 10:31:25 PM org.apache.catalina.core.StandardContext reload
> INFO: Reloading this Context has started
> Apr 22, 2010 10:31:25 PM org.apache.catalina.core.StandardContext start
> SEVERE: Error listenerStart
> Apr 22, 2010 10:31:25 PM org.apache.catalina.core.StandardContext start
> SEVERE: Context [/gbed] startup failed due to previous errors
> My web.xml contains:
>     <listener>
> <listener-class>org.libx.editionbuilder.GCHelper$ShutdownListener</listener-class>
>     </listener>

I think the class needs to be a top level class with a parameter free


> 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?
> Thanks.
>  - Godmar
> [1] See
> http://mail-archives.apache.org/mod_mbox/tomcat-users/201004.mbox/%3cu2s719dced31004132122oc656c456ya25e1a4ba4d4a...@mail.gmail.com%3e
> 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/ServletContextListener.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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