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From Godmar Back <god...@gmail.com>
Subject Re: Q: how to obtain notification when a WebApp is unloaded/reloaded?
Date Sun, 25 Apr 2010 17:24:21 GMT
On Sun, Apr 25, 2010 at 12:29 PM, <users-digest-help@tomcat.apache.org>wrote:

> ---------- Forwarded message ----------
> From: Christopher Schultz <chris@christopherschultz.net>
> To: Tomcat Users List <users@tomcat.apache.org>
> Date: Fri, 23 Apr 2010 12:29:26 -0400
> Subject: Re: Q: how to obtain notification when a WebApp is
> unloaded/reloaded?
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Godmar,
>
> On 4/14/2010 10:20 AM, Godmar Back wrote:
> > 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.
>
> What is your deployment procedure? We use ant for our deployments and
> it's trivial to use the <xslt> task to mutate XML files such as web.xml.
> If you do this, you can set up your deployment process once and not
> worry about it, even if ZK publishes an update.
>
>
My deployment procedure is extremely simple - I do a CVS checkout into the
webapps dir. Immediate deployment (without having to bother creating war
files, etc. etc.)

To reply to an earlier comment that I should use a separate web.xml - I
don't see how this would be possible.

>>
> >>
> <listener-class>org.libx.editionbuilder.GCHelper$ShutdownListener</listener-class>
> >>     </listener>
> >
> > I think the class needs to be a top level class with a parameter free
> > constructor.
>
> I'm not sure if it needs to be top-level, but it will at least need to
> be static. Can you post the code for GCHelper$ShutdownListener?
>
>
Just to be clear - there is no problem with GCHelper$ShutdownListener. Its
methods are invoked on application shutdown the first time. It is a static
class and it doesn't need to be top-level.

The problem arises when the web application is recompiled. Recompilation
works in two steps. First, I remove all files in the classes directory
(/bin/rm -rf WEB-INF/classes), then I run javac to recompile the classes
from a script.

Once Tomcat sees that the files have been removed, it'll declare the web
application dead and stops reloading it.

This is very unfortunate. A work-around I'm trying now is as follows: I
don't delete the .class files when recompiling. This way, Tomcat will never
see them gone. Of course, this will leave stale .class files around when
classes are renamed. However, these can be handled by periodically shutting
down Tomcat and cleaning the WEB-INF/classes directory.

One of my team members uses Eclipse to develop - I assume it will cause the
same problems should Eclipse clean the class directory before recompiling,
as it can be configured to do.

 - Godmar

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