I am currently exploring couple of ways to do this:
1. (It is working for me) is to use java.util.Timer and TimerTask (this API is available since JDK 1.3).
Set one servlet as init-on-startup in your web.xml file, and then have this servlet run your Timer with the tasks
you want. This timer can call anything, even your JSP.
2. Call URL from the UNIX script. Run this as a UNIX cron job. Similar can be done on Win 2K.
3. Use CustomService on WebSphere. This should also work, but I did not try.