获取网络当前时间来代替获取系统当前时间。 搜索了一下，原来获取网络时间有一个协议：Network Time Protocol（NTP： 网络时间协议 ）。 协议有了，那么java有没有相关实现呢。当然也有了。apache的commons-net包下面有ntp的实现。主要的类是：
org.apache.commons.net.ntp.NTPUDPClient 和 org.apache.commons.net.ntp.TimeInfo 看下用法，NTPUDPClient中有方法： public TimeInfo getTime(InetAddress host, int port) throws IOException
public TimeInfo getTime(InetAddress host) throws IOException
package testMaven; import java.io.IOException; import java.net.InetAddress; import java.net.UnknownHostException; import java.text.DateFormat; import java.text.SimpleDateFormat; import java.util.Calendar; import java.util.Date; import org.apache.commons.net.ntp.NTPUDPClient; import org.apache.commons.net.ntp.TimeInfo; import org.apache.commons.net.ntp.TimeStamp; public class GetNtpTime { public static void main(String[] args) { try { NTPUDPClient timeClient = new NTPUDPClient(); String timeServerUrl = "ntp.baijinshan.cn"; // String timeServerUrl = "ntp.aliyun.com"; InetAddress timeServerAddress = InetAddress.getByName(timeServerUrl); TimeInfo timeInfo = timeClient.getTime(timeServerAddress); TimeStamp timeStamp = timeInfo.getMessage().getTransmitTimeStamp(); Date ntpdate = timeStamp.getDate(); Date nowdate = new Date(); DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS"); System.out.println(dateFormat.format(ntpdate)); // NTP时间与本地时间的毫秒差 System.out.println(ntpdate.getTime()-nowdate.getTime()); } catch (UnknownHostException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } }
