JavaWeb用户信息管理系统-用户只能在一处登录

 ServletContext servletContext = this.getServletContext();
                HttpSession temp = (HttpSession) servletContext.getAttribute(users.getUserid()+"");
                if(temp != null){
                    servletContext.removeAttribute(users.getUserid()+"");
                    temp.invalidate();
                }
                servletContext.setAttribute(users.getUserid()+"",session);

       if(window.parent.length > 0){
            window.parent.location="login.jsp";
        }