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From "Sankaranarayanan (Ganesh) Ganapathy" <sganapa...@vitria.com>
Subject RE: [BULK] - Re[2]: [BULK] - Tomcat 4x Classloading
Date Tue, 28 Jan 2003 19:01:21 GMT
Hi Jake,

Appreciate you writing back.

The tomcat class loader heirarchy is thus

sun.misc.Launcher$ExtClassLoader (refers to the lib extensions)
             ^
             |
sun.misc.Launcher$AppClassLoader (refers to system classpath)
             ^
             |
org.apache.catalina.loader.StandardClassLoader ( refers to common repository)
             ^
             |
org.apache.catalina.loader.StandardClassLoader (refers to shared repository)
             ^
             |
org.apache.catalina.loader.WebappClassLoader (refers to the web app repository)

I dont understand how you can claim that the CLASSPATH is never referred.

My question is about the order of reference. I thought the web app repository was the first
thing always refferred by the WebAppClassLoader - but my tests and the code from WebAppClassLoader
seem to point out that the System Classloader (sun.misc.Launcher$AppClassLoader ) is first
given a chance to find the class to avoid overriding the J2SE classes. That being the case
my contention is tomcat documentation on the same is wrong.

Thanx
Ganesh


-----Original Message-----
From: Jacob Kjome [mailto:hoju@visi.com]
Sent: Tuesday, January 28, 2003 10:51 AM
To: Tomcat Users List
Subject: [BULK] - Re[2]: [BULK] - Tomcat 4x Classloading


Hello Sankaranarayanan,

This shouldn't be true.  Apps cannot see the system classpath at all.
Only Tomcat sees that at startup.  Webapps will only see classes in
WEB-INF/lib, WEB-INF/classes, common/endorsed, common/lib,
common/classes, shared/lib, and shared/classes.  Tomcat, itself, also
sees stuff in server/lib and server/classes.

So, if your webapp is actually seeing something set on your system
classpath, then that would be a huge bug in Tomcat as it is designed
to insulate your apps from the classpath entirely.

Jake

Tuesday, January 28, 2003, 12:37:32 PM, you wrote:

SGG> Has anybody seen this as well?

SGG> Any response will be greatly appreicated!

SGG> Thanx
SGG> Ganesh

SGG> -----Original Message-----
SGG> From: Sankaranarayanan (Ganesh) Ganapathy 
SGG> Sent: Monday, January 27, 2003 5:56 PM
SGG> To: tomcat-user@jakarta.apache.org
SGG> Subject: [BULK] - Tomcat 4x Classloading 


SGG> Hi All,

SGG> It has been my observation that the system CLASSPATH classes are loaded in precedence
to the web application class files. i.e if I had a web application class file in my CLASSPATH
and well as my
SGG> web application class repository (WEB-INF/classes) - the one in the system CLASSPATH
is what is loaded. 

SGG> I looked at the source of the web application class loader - I see that the system
classloader is first given a chance to find the class file - to prevent the user from overriding
the standard
SGG> J2SE classes. 

SGG> This is contrary to what the documentation in the apache site says. I have included
the relevant portions with this mail. 

SGG> Am I missing something here?

SGG> --Ganesh

SGG> When a request to load a class from the web application's WebappX class loader is
processed, this class loader will look in the local repositories first, instead of delegating
before looking.
SGG> All other class loaders in Tomcat 4 follow the usual delegation pattern.
SGG> Therefore, from the perspective of a web application, class or resource loading looks
in the following repositories, in this order:
SGG> *       /WEB-INF/classes of your web application 
SGG> *       /WEB-INF/lib/*.jar of your web application 
SGG> *       Bootstrap classes of your JVM 
SGG> *       System class loader classses (described above) 
SGG> *       $CATALINA_HOME/common/classes 
SGG> *       $CATALINA_HOME/common/endorsed/*.jar 
SGG> *       $CATALINA_HOME/common/lib/*.jar 
SGG> *       $CATALINA_HOME/shared/classes 
SGG> *       $CATALINA_HOME/shared/lib/*.jar 


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-- 
Best regards,
 Jacob                            mailto:hoju@visi.com


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