"index.do" isn't a page in the sense that it isn't an HTML or
JSP file. It is a URL that follows the typical
pattern used to tell the
servlet container to hand off the request to the
Struts servlet. I'm pretty sure that this won't work with welcome-file because welcome-file specifies real files.
The typical solution to ensure that a Struts action is the only way into the app is to create an index.jsp file, specify that file in the welcome-file element, and inside the index.jsp file do a redirect to index.do in order to hit your action.