I'm assuming you are looking for Struts 2, if this is the case there are only few good books out there. I own all these books below and they are useful, but they are not as updated as the latest release. My suggestion to you is to keep an eye on the struts 2 wiki and join the mailing list to get the latest information.

1. Practical Apache Struts 2 Web 2.0 Projects (Practical Projects) by Ian Roughley - http://www.amazon.com/Practical-Apache-Struts-Web-Projects/d...

2. Starting Struts 2 by Ian Roughley - http://www.amazon.com/Starting-Struts-2-Ian-Roughley/dp/1430...

3. Struts 2 in Action (In Action) by Don Brown, Chad Davis, and Scott Stanlick - http://www.amazon.com/Struts-2-Action-Don-Brown/dp/193398807...