UrlMapping configuration to expose REST method through URL params
If you have a controller called BookRestController with a getTitle() method then you can configure your UrlMapping.groovy :

It will allow you to call URL like this : http://localhost/my.project/?method=book.getTitle&id=1
You still can have configuration like this for more traditional REST architecture :

Hey, Buster Keaton, is that a dog in your pants or…
This cat is awesome.
( i know…too many animals…)
