this guide is based on Wicket 6. However if you are using an older version you should find this guide useful as well, but it's likely that the code and the snippets won't work with your version.
Wicket in Action is an authoritative, comprehensive guide for Java developers building Wicket-based web applications. This book starts with an introduction to Wicket's structure and components, and moves quickly into examples of Wicket at work. Writ