regd classloader

[E B <he...@yahoo.co.uk>]

Hi
In tc4, whats the difference between "shared" 
and "common" class loader ? From the docs, I
understand
that from the webapp's point of view they are same.
ie., they both give classes to all the webapps. 
Am I correct ?

I want my webapp's classes to be visible and shared
by a soap service. When I put my app's classes in 
shared dir my apache-soap's service could not find the

app's classes. But it worked when I moved them to 
common/classes. So there seems to be something I am 
missing. what is it ?



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Re: regd classloader

["Craig R. McClanahan" <cr...@apache.org>]

On Fri, 19 Oct 2001, simon wrote:

> Date: Fri, 19 Oct 2001 09:16:26 +0900
> From: simon <si...@lexues.co.jp>
> Reply-To: tomcat-user@jakarta.apache.org
> To: tomcat-user@jakarta.apache.org
> Subject: Re: regd classloader
>
> And would it be right to say:
>
> ----- Original Message -----
> From: "Craig R. McClanahan" <cr...@apache.org>
> To: <to...@jakarta.apache.org>
> Cc: <so...@xml.apache.org>
> Sent: Friday, October 19, 2001 12:08 AM
> Subject: Re: regd classloader
>
>
> >
> > Consider a simplified version of the hierarchy:
> >
> >     Common  (package C)
>
> ... are loaded from $TOMCAT_HOME/common/lib
>

Yes, plus unpacked classes from $TOMCAT_HOME/common/classes if it exists.

> >       |
> >     Shared  (package S)
>
> ... are loaded from $TOMCAT_HOME/lib

Yes, plus unpacked classes from $TOMCAT_HOME/classes if it exists.
>
> >       |
> >     Webapp  (package W)
>
> ... are loaded from WEB-INF

Yes, JAR files are loaded from WEB-INF/lib and unpacked classes are loaded
from WEB-INF/classes.
>
> ?
>
> >
> > Craig
>
> simon
>
>
>
Craig

PS:  Note that in Tomcat 4.1 (or if you are using the nightly builds from
the HEAD branch, the Shared class loader has been switched to load from
$TOMCAT_HOME/shared/lib and $TOMCAT_HOME/shared/classes insted of
$TOMCAT_HOME/lib and $TOMCAT_HOME/classes.  This is to improve the
consistency and make it even easier to remember which classloader gets
which classes.

Re: regd classloader

[simon <si...@lexues.co.jp>]

And would it be right to say:

----- Original Message ----- 
From: "Craig R. McClanahan" <cr...@apache.org>
To: <to...@jakarta.apache.org>
Cc: <so...@xml.apache.org>
Sent: Friday, October 19, 2001 12:08 AM
Subject: Re: regd classloader


> 
> Consider a simplified version of the hierarchy:
> 
>     Common  (package C)

... are loaded from $TOMCAT_HOME/common/lib

>       |
>     Shared  (package S)

... are loaded from $TOMCAT_HOME/lib

>       |
>     Webapp  (package W)

... are loaded from WEB-INF

?

> 
> Craig

simon

Re: regd classloader

["Craig R. McClanahan" <cr...@apache.org>]

On Thu, 18 Oct 2001, E B wrote:

> Date: Thu, 18 Oct 2001 10:28:27 +0100 (BST)
> From: E B <he...@yahoo.co.uk>
> Reply-To: tomcat-user@jakarta.apache.org
> To: tomcat-user@jakarta.apache.org, soap-user@xml.apache.org
> Subject: regd classloader
>
> Hi
> In tc4, whats the difference between "shared"
> and "common" class loader ? From the docs, I
> understand
> that from the webapp's point of view they are same.
> ie., they both give classes to all the webapps.
> Am I correct ?
>

The "shared" class loader is visible to all webapps, but NOT to Tomcat's
internal classes.

The "common" class loader is visible to all webapps AND to Tomcat's
internal classes.  A common scenario is where you wanted to use the same
JDBC driver for both a JDBCRealm implementation (so Tomcat needs access to
it) and one or more webapps.

> I want my webapp's classes to be visible and shared
> by a soap service. When I put my app's classes in
> shared dir my apache-soap's service could not find the
>
> app's classes. But it worked when I moved them to
> common/classes. So there seems to be something I am
> missing. what is it ?
>

The most likely cause is that you're trying to load classes from a "lower"
class loader in the hierarchy, which won't work.

Consider a simplified version of the hierarchy:

    Common  (package C)
      |
    Shared  (package S)
      |
    Webapp  (package W)

Now, consider what is visible to classes from each place:

* Classes in the Webapp class loader can see packages W, S, and C

* Classes in the Shared class loader can see packages S and C

* Classes in the Common class loader can see package C only.

In your scenario, it's likely that you had some class in the common
package that was trying to load your app's classes.  That won't work
unless the app's classes are also in the Common loader, OR unless the
service classes take advantage of the Context Class Loader mechanism to
get access to the webapp class loader for the current request:

  ClassLoader cl = Thread.currentThread().getContextClassLoader();
  Class clazz = cl.loadClass("W.Foo");

Craig