(Quick Reference)
                session
Purpose
The 
session object is an instance of the Servlet API's 
HttpSession class
Examples
class UserController {    def logout() {
        log.info "User agent: " + request.getHeader("User-Agent")
        session.invalidate()
        redirect(action: "login")
    }    def login() {}
}Description
The 
HttpSession class is useful for associated session data with a client.
Session attributes which are normally accessible from the 
getAttribute can also be indexed into using the array index operator or de-reference operator:
def user = session["user"]session["user"] = "John"asset "John" == session.user