jsp实现半小时的倒计时页面

<%@ page language="java"  pageEncoding="UTF-8"%><div id="leftTime"></div><script>var leftTime = <%=Integer.parseInt("1800")%>;function showLeftTime(){var leftMinutes = parseInt(leftTime/60);var leftSeconds = parseInt(leftTime%60);if(leftTime < 0){clearInterval(timer);document.location.href = document.location.href;//document.getElementById('leftTime').innerHTML = '';}else{document.getElementById('leftTime').innerHTML = '      如未选择付费方式 ，剩余时间小于5分钟将不允许支付 ，剩余时间：'+leftMinutes+'分'+leftSeconds+'秒';}leftTime--;}var timer = setInterval('showLeftTime()',1000);</script>