JSP 里实时显示系统的时间, 并非客户端时间

<%
Calendar rightNow = Calendar.getInstance();
SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
%>

//从服务器上获取初始时间
var currentDate = new Date(<%=new java.util.Date().getTime()%>);
function run()
{
currentDate.setSeconds(currentDate.getSeconds()+1);
var time = "";
var year = currentDate.getFullYear();
var month = currentDate.getMonth() + 1;
var day = currentDate.getDate();
var hour = currentDate.getHours();
var minute = currentDate.getMinutes();
var second = currentDate.getSeconds();
if(hour < 10){
time += "0"+hour;
}else{
time += hour;
}
time += ":";
if(minute < 10){
time += "0"+minute;
}else{
time += minute;
}
time += ":";
if(second < 10){
time += "0"+second;
}else{
time += second;
}
document.getElementById("dt").innerHTML = year+"年"+month+"月"+day+"日" + time;
}
window.setInterval("run();", 1000);

<span id="dt">自动显示时间</span>

备注：jsp 页面必须不能保存缓存：

<%
  response.addHeader("Pragma", "no-cache");
  response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
  response.addHeader("Cache-Control", "pre-check=0, post-check=0");
  response.setDateHeader("Expires", 0);
%>