I don't really see how an RSS feed would involve a web framework like Struts.
Have a look at an existing feed like this one for one of our forums: http://faq.javaranch.com/RSS/Forum60.rss That's an RSS 2.0 feed, one of the more common formats (there are others formats like RSS 0.91, RSS 0.92, Atom and RDF if you want to cover all the bases). Most of fields are pretty self-explanatory. We keep this as an XML file on the server. It gets updated when there's a new item for that feed, using the XOM XML library; at the same time we check if it contains old items that should be deleted (which we do after 30 days, or sooner if the feed gets too big for the busy forums).
There's no database involved in generating and serving the feeds. As I said, they're XML files.
What you should avoid for performance reasons is to generate a feed whenever someone requests it. You should update the feed files whenever there are changes that need to be reflected in them (we use XOM for that, but any XML library will do).