HDIV 1.3 has just been released including Struts 2 support. HDIV is an open-source project that extends Struts (Struts 1.x and Struts 2) behavior by adding web application level Security functionalities (Integrity, Confidentiality of non editable data and Generic Validations of the Editable Data), maintaining the API and Struts specification.
HDIV 1.3 release has been added as a Struts 2 Plugin. You can download an example (showcase) to understand how HDIV works.
In addition to that there is a quick introduction about HDIV using OWASP top ten 2007 as reference.
You can get more details about HDIV in www.hdiv.org