This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
I would suggest looking at the source code for the version of Struts that you are using. If that fails, I know that the book "Programming Jakarta Struts" has several pages on this topic. I assume that most other Struts books also cover this topic.