General Question about route generation Rails 2+

I have been searching for the definitive answers regarding routes and new controllers, so far no clear statement: Rails 2+ route generation, is it done only once at start up of mongrel? Is this only a dependency on how mongrel does things - looking for updates of config files on the fly or is it a Rails limitation?

You see I also have used servlets and JSP, it seems there you can add new jars and new jsps using them - and they will be picked up with the correct settings. There are some changes in web.xml and I think other configs that require a restart, but I thought that was annoying - especially when doing rapid, iterative development.

However, I thought when I started on Rails 1.x that I had the ability to even add new controllers and not restart - maybe I am wishing I could do that. Is this recent?

Thanks for any links or insight.

- John