Mike writes in this chapter that he didn't feel it would be realistic for the book to build a custom auto-updater here, but he does discuss how they work and presents a high-level algorithm for implementing them. Then, he shows how to take advantage of Java Web Start to ensure that users always have the latest version of your application.
Java Web Start, for example, checks the version of the application on the deployment server every time the local application is run. If the remote version is newer than the local version, then the local version is auto-updated. JWS has more advanced configuration options, including the ability to automatically generate and return incremental updates to JAR files, if possible.
I use JWS as one example auto-update technology. For applications that can live within the JWS sandbox, JWS works quite well.
Mike Clark<br />Author of <a href="http://www.amazon.com/exec/obidos/ASIN/0974514039/ref=jranch-20" target="_blank" rel="nofollow">Pragmatic Project Automation</a>