如何使我的Java应用程序从一些在线时钟获得全球时间

我正在制作一个分布式的Java应用程序，我需要应用程序的两个部分在一个标准时间运行。 由于系统时间可能不同，我在想是否java API包含一些从标准在线源下载时间的类？

Answer 1

您需要使用NTP（网络时间协议）：

http://en.wikipedia.org/wiki/Network_Time_Protocol

以下链接包含一些用于与NTP服务器交互的Java NTP客户端代码：

http://psp2.ntp.org/bin/view/Support/JavaSntpClient

Answer 2

这是我发现的其他代码..我正在使用它。 这使用apache commons库。

// List of time servers: http://tf.nist.gov/service/time-servers.html import java.net.InetAddress; import java.util.Date; import org.apache.commons.net.ntp.NTPUDPClient; import org.apache.commons.net.ntp.TimeInfo; public class TimeLookup { public static final String TIME_SERVER = "time-a.nist.gov"; public static void main(String[] args) throws Exception { NTPUDPClient timeClient = new NTPUDPClient(); InetAddress inetAddress = InetAddress.getByName(TIME_SERVER); TimeInfo timeInfo = timeClient.getTime(inetAddress); long returnTime = timeInfo.getReturnTime(); Date time = new Date(returnTime); System.out.println("Time from " + TIME_SERVER + ": " + time); } } 

Answer 3

注意…. timeInfo.getReturnTime()不会从时间timeserver返回当前时间。 它返回向server发出请求的本地时间。

在调用timeInfo.computeDetails() ，可以通过timeInfo.getOffset().获得偏移量timeInfo.getOffset(). 这将返回本地时间的偏移量（以毫秒为单位）。

计算你可以做的事情的当前时间：

 ... long systemtime = System.currentTimeMillis(); Date realdate = new Date(systemtime + timeInfo.getOffset()); ... 

Answer 4

谢谢Rajendra_Prasad，这是真的

 public static void main(String[] args) throws Exception { NTPUDPClient timeClient = new NTPUDPClient(); InetAddress inetAddress = InetAddress.getByName(TIME_SERVER); TimeInfo timeInfo = timeClient.getTime(inetAddress); long returnTime = timeInfo.getReturnTime(); Date time = new Date(returnTime); long systemtime = System.currentTimeMillis(); timeInfo.computeDetails(); Date realdate = new Date(systemtime + timeInfo.getOffset()); System.out.println("Time from " + TIME_SERVER + ": " + time); System.out.println("Time from " + TIME_SERVER + ": " + realdate); System.out.println(""+time.getTime()); } 

Answer 5

 import java.io.File; import java.io.IOException; import java.net.URL; import java.net.URLConnection; import java.sql.Timestamp; import java.text.ParseException; import java.text.SimpleDateFormat; import java.util.ArrayList; import java.util.Date; import java.util.List; import java.util.Locale; import java.util.Map; public class TimeValidationHook { private static String getServerHttpDate(String serverUrl) throws IOException { URL url = new URL(serverUrl); URLConnection connection = url.openConnection(); Map> httpHeaders = connection.getHeaderFields(); for (Map.Entry> entry : httpHeaders.entrySet()) { String headerName = entry.getKey(); if (headerName != null && headerName.equalsIgnoreCase("date")) { return entry.getValue().get(0); } } return null; } public static void main(String[] args) throws IOException { String serverUrl = args.length > 0 ? args[0] : "https://www.google.co.in"; System.out.println(getServerHttpDate(serverUrl)); Timestamp ts = new Timestamp(System.currentTimeMillis()); System.out.println(ts); //formatter = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US) Tue, 24 Jul 2018 13:25:37 GMT SimpleDateFormat sdf = new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss z", Locale.US); SimpleDateFormat sdf2 = new SimpleDateFormat("yyyy-MM-dd"); Date date2 = null; Date date1 = null; try { date1. = sdf.parse(getServerHttpDate(serverUrl)); date2 = sdf2.parse(ts.toString()); } catch (ParseException e) { e.printStackTrace(); } System.out.println("date1 : " + sdf2.format(date1)); System.out.println("date2 : " + sdf2.format(date2)); if (date1.compareTo(date2) > 0) { System.out.println("Date1 is after Date2"); List cmd = new ArrayList(); cmd.add("hg rollback"); ProcessBuilder pb = new ProcessBuilder(cmd); pb.directory(new File("E:\\repos\\Trunk")); Process p = pb.start(); } else if (date1.compareTo(date2) < 0) { System.out.println("Date1 is before Date2"); } else if (date1.compareTo(date2) == 0) { System.out.println("Date1 is equal to Date2"); } else { System.out.println("How to get here?"); } } }