- checkout this repo (see above)
- type "mvn jetty:run" to start the sample application
- open http://localhost:8080/wicket-download-sample/ in your browser

How to implement that the Ajax update will performed and the download
of a resource will be initiated is well discribed in the wicket wiki:
https://cwiki.apache.org/WICKET/ajax-update-and-file-download-in-one-blow.html