Are you asking how you can direct a search to an appropriate action based on a parameter value? If so, look at using the org.apache.struts.RelayAction. This action looks for a given parameter and uses its value to look up a forward (to another action).
For instance, if you passed aURL to the Struts controller like:
http://a.b.com/Search.do?dispatch=books the RelayAction would check the mappings for an ActionForward named 'books' and forward the action to it. For example:
<action
path="/Search"
type="org.apache.struts.scaffold.RelayAction"
scope="request"
validate="false">
<forward name="books" path="/SearchBooks.do" />
<forward name="cars" path="/SearchBooks.do" />
<forward name="music" path="/SearchBooks.do" />
</action>
Hope this helps.
Darryl