In your Action, you can just return null instead of an
ActionForward

    public ActionForward perform(ActionMapping mapping,
                 ActionForm form,
                 HttpServletRequest request,
                 HttpServletResponse response)
    throws IOException, ServletException {
        response.setContentType("text/plain");
        response.getWriter().print("Hello World");
        return (null);
    };

HTH -Ted