How do you change the default homepage in a Grails application?

Add this in UrlMappings.groovy

 "https://stackoverflow.com/" {
    controller = "yourController"
    action = "yourAction"
 }

By configuring the URLMappings this way, the home-page of the app will be yourWebApp/yourController/yourAction.

(cut/pasted from IntelliGrape Blog)