How to Fetch Time Accurately from Internet Time Servers in Java?

Fetching Time Accurately from Internet Time Servers in Java

Accurately synchronizing time is crucial for many applications. Relying solely on a local system's time settings can lead to inconsistencies. This article explores how to leverage Internet time servers like in.pool.ntp.org to obtain the authoritative Greenwich Mean Time (GMT) in Java.

Java Library for Time Synchronization

To retrieve time from an external server, Java provides the javax.time.ntp library. It allows access to the Network Time Protocol (NTP), a standardized protocol for time synchronization.

Retrieving Time Using NTP

Here's a code snippet to retrieve time from a time server:

import javax.time.ntp.NTPUDPClient;
import javax.time.ntp.TimeInfo;
import java.net.InetAddress;
import java.util.Date;

public class TimeSync {

    public static void main(String[] args) throws Exception {
        // Specify the time server hostname
        String TIME_SERVER = "in.pool.ntp.org";

        // Create an NTP UDP client
        NTPUDPClient timeClient = new NTPUDPClient();

        // Get the server's IP address
        InetAddress inetAddress = InetAddress.getByName(TIME_SERVER);

        // Retrieve time information from the server
        TimeInfo timeInfo = timeClient.getTime(inetAddress);

        // Get the time at which the packet was sent by the server
        long returnTime = timeInfo.getMessage().getTransmitTimeStamp().getTime();

        // Convert the epoch time to a Date object
        Date time = new Date(returnTime);

        // Print the synchronized time
        System.out.println("Current GMT time: " + time);
    }
}

Note: NTP servers typically provide time stamps with high precision. For optimal accuracy, consider making multiple requests to the server and averaging the results.

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