Most of us who deploy on Websphere have at some point encountered classloading issues. Websphere provides a lot of libraries which are loaded by default (parent first) before the libraries supplied by the application. IBM explains the classloading order on this site:
http://www.ibm.com/developerworks/websphere/library/techarticles/0112_deboer/deboer.html

At my current position some Websphere installations have installed feature packs while others have not. You can view which feature packs are installed by running:
versionInfo.bat/sh from the Profile directory (e.g.: /opt/IBM/WebSphere/AppServer/profiles/AppSrv01/bin).
This can also cause version mismatches.

The following examples are from Websphere 6.1

Viewing classloader order:
You can view the order in which the libraries are loaded by following these links in the admin console:
Enterprise Applications > [ear module] > Manage Modules > [ war module] -> view module classloader.

You can expand the tree or export the contents of the Classloader viewer to a XML-file. Here you can easily tell if a library is provided by Websphere or your application.

Changing classloader order:
To change the classloading order follow the following link:
Enterprise Applications > [ear module] > Class loader

You can set the value of Class loader order to parent-last or application-first (depends on Websphere version) to make sure the jar-files of your application are loaded first. If the jar-files are also present in WEB-INF/lib you can alter the setting in:
Enterprise Applications >[ear module] > Manage Modules > [war module] (again parent-last or application-first)

If you cannot change these settings and you are deploying through WTP then you must change the file: application.xml.  You can enter these settings at the deployment tab (maybe only in RAD?)

Creating your own classloader
Another way of preventing Websphere to load its own libraries first is to use a shared library.Jar-files in the shared-library are automatically placed on the classpath. You can create a special classloader to make sure certain libraries are loaded before anything else:

Application servers > server1 > Class loader

Select ‘new classloader’ and choose ‘Classes loaded with application class loader first’. After you have created this classloader you can attach your shared library to this loader.  After this you can restart your application server for these changes to take effect. For me this is the cleanest solution but remember this affects all applications deployed on the server. The benefit is that you can change the classloading order on a per-library basis i.s.o. changing the order for all the libraries in the application.

Dit bericht is gepost op 18 September 2009 om 12:06 pm uur en is geplaatst in Algemeen, Middleware. Je kunt alle reacties op dit bericht volgen via de RSS 2.0 feed. Je kunt een reactie achter laten of trackback vanaf je eigen site.