Getting time from public time server using TimeTCPClient

问题

I try to use the following code to obtain time from public time server.

package aaa;

import java.util.Arrays;
import java.util.List;

import org.apache.commons.net.TimeTCPClient;

public final class Main
{
    public static java.util.Date getNTPDate() {
        List<String> hosts = Arrays.asList("0.pool.ntp.org");

        for (String host : hosts) {
            TimeTCPClient client = new TimeTCPClient();
            // We want to timeout if a response takes longer than 5 seconds
            client.setDefaultTimeout(5000);
            try {
                client.connect(host);
                java.util.Date ntpDate = client.getDate();
                client.disconnect();
                // Just to be extra caution.
                if (ntpDate != null) {
                    return ntpDate;
                }
            }
            catch (java.net.SocketException exp) {
                exp.printStackTrace();
            }
            catch (java.io.IOException exp) {
                exp.printStackTrace();
            }
        }
        return null;
    }

    public static final void main(String[] args)
    {
        System.out.println(getNTPDate());
    }

}

However, all the time, I am getting java.net.ConnectException: Connection timed out: connect

I had tried to google for several different time server. However, non of them work. I was wondering, is the problem lies on my code, or the server I choose?

回答1:

NTP is a different protocol than the time protocol. NTP servers only talk over port UDP/123. Time servers use TCP/37 (which TimeTCPClient appears to implement correctly).

If you want to get a remote time, use an appropriate server (ntp.xs4all.nl appears to be listening on the time port).

回答2:

You can use the correct approach:

import java.io.IOException;
import java.net.InetAddress;
import java.util.Date;

import org.apache.commons.net.ntp.NTPUDPClient;
import org.apache.commons.net.ntp.TimeInfo;

public final class PublicServerTime {

    public static Date getNTPDate() {

        String[] hosts = new String[]{
            "ntp02.oal.ul.pt", "ntp04.oal.ul.pt",
            "ntp.xs4all.nl"};

        NTPUDPClient client = new NTPUDPClient();
        // We want to timeout if a response takes longer than 5 seconds
        client.setDefaultTimeout(5000);

        for (String host : hosts) {

            try {
                InetAddress hostAddr = InetAddress.getByName(host);
                System.out.println("> " + hostAddr.getHostName() + "/" + hostAddr.getHostAddress());
                TimeInfo info = client.getTime(hostAddr);
                Date date = new Date(info.getReturnTime());
                return date;

            }
            catch (IOException e) {
                e.printStackTrace();
            }
        }

        client.close();

        return null;

    }


    public static final void main(String[] args) {

        System.out.println(getNTPDate());

    }

回答3:

Source:

public class NTPService {

    private final static Logger logger = Logger.getLogger(NTPService.class);
    private final static int TIMEOUT = 5000;
    private final static List<String> hostList = 
                                   Arrays.asList("time.windows.com", "nl.pool.ntp.org");

    private final NTPUDPClient client = new NTPUDPClient();

    public NTPService() {
        client.setDefaultTimeout(TIMEOUT);
    }

    public LocalDateTime getNTPDateTime() {
        for (final String host : hostList) {
            final LocalDateTime localDateTime = getNTPDateTime(host);
            if (null != localDateTime) {
                return localDateTime;
            }
        }
        return null;
    }

    private LocalDateTime getNTPDateTime(final String host) {
        try {
            client.open();
            return convertToLocalDateTime(
                    TimeStamp.getNtpTime(client.getTime(InetAddress.getByName(host))
                                  .getReturnTime()).getTime());
        } catch (final Exception exp) {
            logger.warn(String.format("%s: failed to update NTP", host), exp);
            return null;
        } finally {
            if (client.isOpen()) {
                client.close();
            }
        }
    }

    private LocalDateTime convertToLocalDateTime(final long value) {
        return LocalDateTime.ofInstant(Instant.ofEpochMilli(value),
               ZoneId.systemDefault());
    }
}

Usage:

System.out.println(DateTimeFormatter.ofPattern("yyyy.MM.dd HH:mm:ss").
                   format(new NTPService().getNTPDateTime()));

来源：https://stackoverflow.com/questions/7081262/getting-time-from-public-time-server-using-timetcpclient