How can I get the session from within a command object?

I have tried:

import org.springframework.security.context.SecurityContextHolder as SCH

class MyCommand {
   def session = RCH.currentRequestAttributes().getSession()
}

This throws

java.lang.IllegalStateException: No thread-bound request found: Are you referring to request attributes outside of an actual web request, or processing a request outside of the originally receiving thread? If you are actually operating within a web request and still receive this message, your code is probably running outside of DispatcherServlet/DispatcherPortlet: In this case, use RequestContextListener or RequestContextFilter to expose the current request.