<%
        String loginURL = "login.jsp";
        String user = (String) session.getAttribute("username");
    
        if (user == null) {
            response.setHeader("Refresh", "1;URL=" + loginURL);
            out.println("成功退出！1秒后跳转登录界面！");
        }
    %>

------解决方案--------------------
JScript code

<script type="text/javascript">
   var timer = window.setInterval("Timer()",1000);//启用定时倒计
   var secs = 5;
   function Timer() {
      secs--;
      document.getElementById("btnShow").innerHTML = "倒计时：[" + secs + "]";
      if(secs == 0){
          window.clearInterval(timer);//清楚定时任务
          window.location.href="地址";
      }
    }
</script>