https://my.oschina.net/rupertwong/blog/538913
apache的commons-net包下面有ntp相关的实现类,主要类有:
org.apache.commons.net.ntp.NTPUDPClient
org.apache.commons.net.ntp.TimeInfo
类NTPUDPClient中相关方法:
TimeInfo getTime(InetAddress host, int port) throws IOException
TimeInfo getTime(InetAddress host) throws IOException
其中,第二个重载方法使用协议规范默认端口:123。
Java代码段:
public static void main(String[] args) throws IOException {
try {
NTPUDPClient timeClient = new NTPUDPClient();
String timeServerUrl = "202.120.2.101";
InetAddress timeServerAddress = InetAddress.getByName(timeServerUrl);
TimeInfo timeInfo = timeClient.getTime(timeServerAddress);
TimeStamp timeStamp = timeInfo.getMessage().getTransmitTimeStamp();
Date date = timeStamp.getDate();
System.out.println(date);
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
System.out.println(dateFormat.format(date));
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
运行结果为:
Thu Dec 03 16:16:50 CST 2015
2015-12-03 04:16:50
附:常用速度较快NTP服务器地址:
ntp.sjtu.edu.cn 202.120.2.101 (上海交通大学网络中心NTP服务器地址)
time-a.nist.gov 129.6.15.28 NIST, Gaithersburg, Maryland
time-b.nist.gov 129.6.15.29 NIST, Gaithersburg, Maryland
time-a.timefreq.bldrdoc.gov 132.163.4.101 NIST, Boulder, Colorado
time-b.timefreq.bldrdoc.gov 132.163.4.102 NIST, Boulder, Colorado
time-c.timefreq.bldrdoc.gov 132.163.4.103 NIST, Boulder, Colorado