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From "Benjamin Armintor" <>
Subject RE: Extending GenericPrincipal/RealmBase: Essentially a classloader question
Date Thu, 15 Apr 2004 16:34:14 GMT
Can your webapps see GenericPrincipal?  Looking at the JavaDocs for the Catalina api, it looks
like the session façade your get app gets is going to have access to a
(likely also a façade), not a GenericPrincipal.  Maybe instead of extending a class in the
server/Catalina classloader, you could implement another subclass of,
and have that class loaded in the common classloader.  

Benjamin J. Armintor
Systems Analyst
ITS-Systems: Mainframe Group
University of Texas - Austin
tele: (512) 232-6562

-----Original Message-----
From: John H [] 
Sent: Thursday, April 15, 2004 11:25 AM
To: Tomcat Users List
Subject: Extending GenericPrincipal/RealmBase: Essentially a classloader question

HI all,

He have implemented our own realm and principal buy extending org.apache.catalina.realm.RealmBase
and GenericPrincipal.

(Using TC5.0.19 on Solaris and Windows. Realm defined in <Context>.)

By doing this, however, we've got ourselves into sort of a catch 22 in terms of classloading.
Hopefully someone can offer some assistance.

I've referenced the Class Loader HOW-TO at,
so I'll use it's terminology.

RealmBase and GenericPrincipal are located in catalina.jar, which resides physically in server/lib.
The howo defines this jar as in the Catalina class loader. The definition says that the Catalina
classes are totally invisible to web applications, which seems true enough. In order to extend
these, I must locate my jar in server/lib. So far so good.

The problem is that I need to use my extension of GenericPrincipal within my webapps.

I tried moving my jar to common/lib, since, according to the parent tree in the howto, it
is visible to both the Catalina branch and the webapp branch. Doing this causes a NoClassDefFoundError
for GenericPrincipal. Apparently since the Catalina classloader is below the common classloader,
it can't find GenericPrincipal. 

The only solution that appears to work is moving the entire contents of server/lib to common/lib,
essentially 'promoting' all of the classes normally in the Catalina class loader to the common
class loader. 

Is this the best solution? It seems to me that I should be able to extend RealmBase/GenericPrincipal
without having to move jars around. 

Any ideas?


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