Network Time Protocol (ntp)

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Android

public class Util {
    //NTP server list: http://tf.nist.gov/tf-cgi/servers.cgi
    public static final String TIME_SERVER = "pool.ntp.org";

    public static long getCurrentNetworkTime() {
        NTPUDPClient lNTPUDPClient = new NTPUDPClient();
        lNTPUDPClient.setDefaultTimeout(3000);
        long returnTime = 0;
        try {
            lNTPUDPClient.open();
            InetAddress lInetAddress = InetAddress.getByName(TIME_SERVER);
            TimeInfo lTimeInfo = lNTPUDPClient.getTime(lInetAddress);
            // returnTime =  lTimeInfo.getReturnTime(); // local time
            returnTime = lTimeInfo.getMessage().getTransmitTimeStamp().getTime();   //server time
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lNTPUDPClient.close();
        }

        return returnTime;
    }
}

Unit Test

public class NtpUnitTest {
    @Test
    public void ntp_isCorrect() throws Exception {
        long longTime = Util.getCurrentNetworkTime();
        Date date = new Date(longTime);
        // You can specify styles if you want
        DateFormat format = DateFormat.getDateInstance();
        // Set time zone information if you want.
        String text = format.format(date);

        System.out.print(text);

        Calendar calendar = new GregorianCalendar();
        calendar.setTime(date);
        int year = calendar.get(Calendar.YEAR);
        //Add one to month {0 - 11}
        int month = calendar.get(Calendar.MONTH) + 1;
        int day = calendar.get(Calendar.DAY_OF_MONTH);
        int hour = calendar.get(Calendar.HOUR_OF_DAY);
        int minute = calendar.get(Calendar.MINUTE);
        int second = calendar.get(Calendar.SECOND);
        int millis = calendar.get(Calendar.MILLISECOND);

        assertEquals(2017, year);
        assertEquals(7, month);
        assertEquals(4, day);
        assertEquals(12, hour);
//        assertEquals(6, minute);
    }
}