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From "Aaron Mulder" <ammul...@alumni.princeton.edu>
Subject Re: Classloader Hierarchy and hidden-classes
Date Thu, 14 Sep 2006 19:29:49 GMT
Since we have multi-parent class loaders, it may be that there's more
than one path to the offending server-level JAR.

For example, if you want to make commons-logging hidden, and you put
the hidden-classes at the EAR level, but the WAR has a dependency on a
database pool, then the WAR could find the server commons-logging
through either the EAR-parent path or the database-pool-parent path.
The solution in that case would be to move the database pool
dependency to the EAR too, so the hidden-classes in the EAR would
work.  But again, there may be several such dependencies at the WAR
level.  Actually, if it really was commons-logging, you might not be
able to avoid this problem, since the WAR will automatically depend on
either the Tomcat or Jetty module, which gives yet another route.
Hmmm.  It's almost like we need a way to say "load only from EAR" or
"load only from dependency X"...

Thanks,
     Aaron

On 9/13/06, Shan Karthic <shan.karthic@gmail.com> wrote:
> I am using geronimo 1.1.1-rc3.  I am using the release candidate instead of
> 1.1 since 1.1.1 fixes GERONIMO-2125.
>
> Is there anyway I can specify, for everything under the application
> classloader (including child classloaders of the application classloader,
> such as WAR classloaders), that the classes loaded by application class
> loader are visible but not the ones loaded above the application
> classloader?
>
> I want to hide some classes loaded by the server inside my application.  If
> I use hidden-classes I am able to hide the classes loaded by current
> classloader's parents.  The problem I face is if I use hidden-classes at WAR
> level it hides the same classes loaded by EAR/application classloader as
> well.  If I use hidden-classes only at application level and not at WAR
> level, it does not hide the classes loaded by the server from the WAR class
> loader.  It looks like child classloaders do not know of hidden-classes
> specified at parent classloader level.  Is there any reason it is so?
>
> I started out trying to force my application to use its own log4j
> configuration accessed through commons logging.  So I had to hide
> org.apache.commons.logging, org.apache.log4j, org.apache.geronimo.kernel.log
> loaded by the server.  An utility jar in the application manages references
> to Log objects.  The utility is used by EJBs and other utilities and WAR.
>
> I am able to get the desired behaviour by hiding the classes at both app
> level and at WAR level with inverse-classloading at WAR level.  If I do not
> hide at WAR level, WAR class loader sees the classes loaded by the server.
> If I hide at WAR level without inverse-classloading, WAR class loader does
> not see log4j classes loaded by the app class loader.  But (I think so but
> my interpretation of the diagnostic messages from commons logging may be
> wrong), due to the way Log references are stored in a hierarchy of class
> loaders, there seems to be assignments between log4j classes loaded by app
> and WAR classloaders which results in errors.
>
> Now the problem is, since I have enabled inverse-classloading at WAR level,
> classes loaded by WAR classloader do not see any config/properties files
> available under the EAR root.  I also think the singleton LogManager the
> application uses is no longer singleton really as it is loaded separately by
> the WAR and EAR classloaders.
>
> As I see it, if I can hide the required classes at app classloader level,
> that propagates to all child classloaders without hiding the classes loaded
> the app classloader itself, that will help in resolving the problem.  I
> searched but could not find whether there is anyway to do that.
>
> Thanks and regards,
> Shankar.
>

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