Grails and dynamic controller names in UrlMappings

I was creating some REST web services and I needed to map a URL like “/api/1.0/recipes” to a controller called RecipesRestController. It took me a while to work out how to generate a dynamic controller name from the request path. The trick is not to use $controller, it doesn’t seem to work, so instead I renamed it $aController.

---

class UrlMappings {

    static mappings = {

        "/$controller/$action?/$id?"{

            constraints {

                // apply constraints here

            }

        }

        "/"(view:"/index")

        "500"(view:'/error')

        "/api/1.0/$aController"{

            controller={"${params.aController}Rest"}

            action=[GET:"list", POST:"save"]

        }

        "/api/1.0/$aController/$id"{

            controller={"${params.aController}Rest"}

            action=[GET:"show",  PUT:"update", DELETE:"delete"]

        }

    }

}

OR

import org.codehaus.groovy.grails.commons.ApplicationHolder

class UrlMappings {
  static mappings = {        
    for( controllerClass in ApplicationHolder.application.controllerClasses) {
      // Admin Controllers first
      if( controllerClass.name.startsWith("Admin")){
        // note... fixes the case so that AdminUserController maps to /admin/user
        "/admin/${controllerClass.name[5].toLowerCase() + controllerClass.name[6..-1]}/$action?/$id?" {
          controller = "admin${controllerClass.name[5..-1]}".toString()
        }
      }
    }
  }
}

OR

    "/admin/$controller/$action?/$id?"{
        controller = {
            def controllerName = (request.requestURI - request.contextPath).split('/')[2]

            // or
            //def controllerName = request.servletPath.split('/')[2]

            "${controllerName}Admin"
        }
    }