This filter can be used to server an index file for a directory
when no index file actually exists (thus the web.xml mechanism does
This filter will dispatch requests to a directory (URLs ending with /)
to the welcome URL determined by the "welcome" init parameter. So if
the filter "welcome" init parameter is set to "index.do" then a request
to "/some/directory/" will be dispatched to "/some/directory/index.do" and
will be handled by any servlets mapped to that URL.
Requests to "/some/directory" will be redirected to "/some/directory/".