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.
I would suggest you use an ajax framework like Dojo or jQuery. Although I use plain Dojo in my Struts web applications to implement ajax, you may prefer to use jQuery since Struts provides a jQuery plugin that allows you to use Struts tags to provide ajax functionality. Please see the following link for more general info: http://struts.apache.org/2.3.1/docs/ajax.html