This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori 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.