Create exception methods to catch controlled exceptions for REST

[ppazos]

And return the right HTTP status instead of a view that displays the exception.

Check:

http://mrhaki.blogspot.com.uy/2014/05/grails-goodness-exception-methods-in.html
https://stackoverflow.com/questions/17935485/is-it-possible-for-a-service-to-return-a-404-response
http://www.oodlestechnologies.com/blogs/How-to-Handle-Exception-In-grails-Controller
https://stackoverflow.com/questions/17192336/exception-handling-in-grails-controllers