This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
validation.xml comes with struts validator framework. It gives you certain set of validation rules, which you can use conveniently from xml files. But with ActionForm validate method you need to write your validation rules programmatically. So I think validator framework makes it more convenient for you.