Caching
Some users have found that IE will cache the response from the AJAX request. This could be due to browser/page settings, but a forced workaround is to timestamp the URL:

var urlstr = "./admin?reqId=0&ts=" + new Date().getTimeStamp();

To XML or Not to XML
Not to XML. Some AJAX designers happily dispense with XML and send the response as plain text:

response.setContentType("text/plain");

This clearly depends on your client-side requirement and how loosely coupled the client is from the data required. A simple text response would suffice for a text alert. However, the advantage of the XML model for this article is that the response data can be elaborated further to refine both the status and status-related data. This article demonstrates how you'd parse a more complicated response that the client may have to code to accept.

Conclusion
AJAX presents architectural opportunities that shouldn't be overshadowed by the rich-client frenzy. This article has leveraged the architectural advantage AJAX can provide while addressing the technical requirements for both capacity and security that more exotic uses of this technology will demand.

References

• http://java.sun.com/j2ee/1.4/docs/api/javax/ management/NotificationFilterSupport.html - Details the alert types functionality
• http://e-docs.bea.com/wls/docs81/jmx/notifications.html - Details the use of WebLogic MBean Notifications for remote listeners
• http://e-docs.bea.com/wls/docs81/ConsoleHelp/startup_shutdown.html - Configuring start-up and shutdown classes in WebLogic Server 8.1