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From delbd <>
Subject Re: WebappClassLoader - don't understand what's happening
Date Thu, 02 Jun 2005 10:32:33 GMT
This indeed should not happen as this would break sun specs. I would be quite 
surprised it it was at all possible :/
How did you conclude the webappclassloader is sharing the class between 
webapps in your case?

Are you sure you are not mistakenly using a shared class?

Not only does every webapp has his very own webappclassloader, but if you 
reload the webapp (using the manager/html interface) this should also create 
a new webclassloader and reload all classes (did you check it was the case?).

Am also using tomcat 5.5.7 here, with jdk 1.4.2_05-b04 and we didn't notice 
such a problem. We can deploy several webapps, all using a library in 
WEB-INF/lib which is crating singletons. All webapp has it's own sets of 

Could it be that you are in fact doing such scenario?

- create an object of class A in webapp1 using webappclassloader1
- push this object to some library shared between webapplications
- retrieve the object from shared library in webapp2 (as this is via a shared 
library, it's possibile to do and you and up manipulating in webapp2 an 
object who's classloader is webappclassloader1)
- in webapp2, calls something like a.createB() to get an object of class B
and be surprised that the class of B was created using webappclassloader1

Le Jeudi 2 Juin 2005 10:59, Herrmann, Sascha (GE Healthcare) a écrit :
> We are facing a problem with Tomcats WebappClassLoader.
> We deploy several of our own applications on one Tomcat server.
> It seems that the WebappClassLoaderS are not isolated but share classes
> instead. Why would that be?
> Judging from the (well, outdated) classloader documentation, this should
> never happen.
> If an application tries to use a class, and the class is in a jar in its
> WEB_INF\lib directory,
> then the class should be loaded by the application's very own
> WebappClassLoader. It should not be available to
> other WebappClassLoaderS, isn't that correct? I quote:
> "All unpacked classes and resources in the /WEB-INF/classes directory of
> your web application archive, plus classes and resources in JAR files
> under the /WEB-INF/lib directory of your web application archive, are
> made visible to the containing web application, **but to no others**."
> Instead of sharing the class, the second WebappClassLoader should load
> the class again, shouldn't it?
> So why does a WebappClassLoader here re-use a class already loaded by
> the WebappClassLoader of another application?
> We're running 5.5.7 on JDK 142_08.
> Thanks in advance!
> Sascha Herrmann
> Engineering (Java)
> GE Healthcare
> Technologies
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David Delbecq
Royal Meteorological Institute of Belgium

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