Yes, using the shared classloader seems like an obvious and easy option for 
sharing the objects between the web applications. However, like the previous 
author notes relying on the classloader can bring up some issues like 
introducing new dependencies and reducing the web application incapsulation. 

That is why the alternative way of sharing objects between the web applications 
is worth considering I guess. As I noted before one can achive this using the 
java object serialization or the java.beans xml encoding. This technique allows 
one to effectively eliminate the class loader information from the type and 
thus share the objects between the web applications without using the shared 
classloader.

BTW, one can not use the Tomcat JNDI tree as a place to share the objects 
between the web apps, because Tomcat does not allow one to put an arbitrary 
object into the JNDI tree. One possible way is to utilize the system 
MBeanServer.

--Seva

-----Original Message-----
From: Jon Wingfield [mailto:[EMAIL PROTECTED] 
Sent: Tuesday, October 04, 2005 9:47 AM
To: Tomcat Users List
Subject: Re: ClassCastException while sharing objects accross applications

What Chuck says is right.
This approach has a few gotchas though, especially if ClassX is complex 
and references many other objects loaded from the same (WebApp) 
classloader. You can end up with a lot of classes up in the common 
repository. >-o

Make ClassX an interface, if you can. That way only the interface (and 
any referenced types) need go in common. Refactoring here we go :)

HTH,

Jon

Caldarale, Charles R wrote:
>>From: Andrés Glez. [mailto:[EMAIL PROTECTED] 
>>Subject: Re: ClassCastException while sharing objects accross 
>>applications
>>
>>What about using JNDI to share objects between webapps?
> 
> 
> Won't change anything, due to the previously noted classloader-specific 
> casting issue.  What should work (haven't tried it) is to put the defining 
> class for the object of interest in shared/classes or shared/lib (if packaged 
> in a jar), and remove it from each webapp.  This will create the class under 
> a classloader visible to both webapps.
> 
> See:
> http://jakarta.apache.org/tomcat/tomcat-5.5-doc/class-loader-howto.html
> for more info.
> 
>  - Chuck
> 
> 
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