forward using RequestDispatcher

I using ServletFilter to check whether the user is authenticated or has permissions to access resource. In case of not authenticated or not authorized I must redirect user to some page (Error Page ) . For this I must use RequestDispatcher to forward him to error page. If I do this I mu

forwarding to a global forward using RequestDispatcher

How can I pass a Struts Global forward to request.getRequestDispatcher("struts global Forward).forward(request,response) or How can I forward to a struts Global forward using RequestDispatcher. I tried passing struts global forward , but always I got page not found error .