Commons Net example source code file (NTPClient.java)

This example Commons Net source code file (NTPClient.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Commons Net tags/keywords

gps, inetaddress, io, local, local, long, n/a, net, network, ntpudpclient, reference, reference, socketexception, string, string, text, timestamp, timestamp

The Commons Net NTPClient.java source code

package examples.ntp;
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


import java.io.IOException;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.text.NumberFormat;

import org.apache.commons.net.ntp.*;

/***
 * This is an example program demonstrating how to use the NTPUDPClient
 * class. This program sends a Datagram client request packet to a
 * Network time Protocol (NTP) service port on a specified server,
 * retrieves the time, and prints it to standard output along with
 * the fields from the NTP message header (e.g. stratum level, reference id,
 * poll interval, root delay, mode, ...)
 * See <A HREF="ftp://ftp.rfc-editor.org/in-notes/rfc868.txt"> the spec 
 * for details.
 * <p>
 * Usage: NTPClient <hostname-or-address-list>
 * <br>
 * Example: NTPClient clock.psu.edu
 *
 * @author Jason Mathews, MITRE Corp
 ***/
public final class NTPClient
{

    private static final NumberFormat numberFormat = new java.text.DecimalFormat("0.00");

    /**
     * Process <code>TimeInfo object and print its details.
     * @param info <code>TimeInfo object.
     */
    public static void processResponse(TimeInfo info)
    {
        NtpV3Packet message = info.getMessage();
        int stratum = message.getStratum();
        String refType;
        if (stratum <= 0)
            refType = "(Unspecified or Unavailable)";
        else if (stratum == 1)
            refType = "(Primary Reference; e.g., GPS)"; // GPS, radio clock, etc.
        else
            refType = "(Secondary Reference; e.g. via NTP or SNTP)";
        // stratum should be 0..15...
        System.out.println(" Stratum: " + stratum + " " + refType);
        int version = message.getVersion();
        int li = message.getLeapIndicator();
        System.out.println(" leap=" + li + ", version="
                + version + ", precision=" + message.getPrecision());

        System.out.println(" mode: " + message.getModeName() + " (" + message.getMode() + ")");
        int poll = message.getPoll();
        // poll value typically btwn MINPOLL (4) and MAXPOLL (14)
        System.out.println(" poll: " + (poll <= 0 ? 1 : (int) Math.pow(2, poll))
                + " seconds" + " (2 ** " + poll + ")");
        double disp = message.getRootDispersionInMillisDouble();
        System.out.println(" rootdelay=" + numberFormat.format(message.getRootDelayInMillisDouble())
                + ", rootdispersion(ms): " + numberFormat.format(disp));

        int refId = message.getReferenceId();
        String refAddr = NtpUtils.getHostAddress(refId);
        String refName = null;
        if (refId != 0) {
            if (refAddr.equals("127.127.1.0")) {
                refName = "LOCAL"; // This is the ref address for the Local Clock
            } else if (stratum >= 2) {
                // If reference id has 127.127 prefix then it uses its own reference clock
                // defined in the form 127.127.clock-type.unit-num (e.g. 127.127.8.0 mode 5
                // for GENERIC DCF77 AM; see refclock.htm from the NTP software distribution.
                if (!refAddr.startsWith("127.127")) {
                    try {
                        InetAddress addr = InetAddress.getByName(refAddr);
                        String name = addr.getHostName();
                        if (name != null && !name.equals(refAddr))
                            refName = name;
                    } catch (UnknownHostException e) {
                        // some stratum-2 servers sync to ref clock device but fudge stratum level higher... (e.g. 2)
                        // ref not valid host maybe it's a reference clock name?
                        // otherwise just show the ref IP address.
                        refName = NtpUtils.getReferenceClock(message);
                    }
                }
            } else if (version >= 3 && (stratum == 0 || stratum == 1)) {
                refName = NtpUtils.getReferenceClock(message);
                // refname usually have at least 3 characters (e.g. GPS, WWV, LCL, etc.)
            }
            // otherwise give up on naming the beast...
        }
        if (refName != null && refName.length() > 1)
            refAddr += " (" + refName + ")";
        System.out.println(" Reference Identifier:\t" + refAddr);

        TimeStamp refNtpTime = message.getReferenceTimeStamp();
        System.out.println(" Reference Timestamp:\t" + refNtpTime + "  " + refNtpTime.toDateString());

        // Originate Time is time request sent by client (t1)
        TimeStamp origNtpTime = message.getOriginateTimeStamp();
        System.out.println(" Originate Timestamp:\t" + origNtpTime + "  " + origNtpTime.toDateString());

        long destTime = info.getReturnTime();
        // Receive Time is time request received by server (t2)
        TimeStamp rcvNtpTime = message.getReceiveTimeStamp();
        System.out.println(" Receive Timestamp:\t" + rcvNtpTime + "  " + rcvNtpTime.toDateString());

        // Transmit time is time reply sent by server (t3)
        TimeStamp xmitNtpTime = message.getTransmitTimeStamp();
        System.out.println(" Transmit Timestamp:\t" + xmitNtpTime + "  " + xmitNtpTime.toDateString());

        // Destination time is time reply received by client (t4)
        TimeStamp destNtpTime = TimeStamp.getNtpTime(destTime);
        System.out.println(" Destination Timestamp:\t" + destNtpTime + "  " + destNtpTime.toDateString());

        info.computeDetails(); // compute offset/delay if not already done
        Long offsetValue = info.getOffset();
        Long delayValue = info.getDelay();
        String delay = (delayValue == null) ? "N/A" : delayValue.toString();
        String offset = (offsetValue == null) ? "N/A" : offsetValue.toString();

        System.out.println(" Roundtrip delay(ms)=" + delay
                + ", clock offset(ms)=" + offset); // offset in ms
    }

    public static final void main(String[] args)
    {
        if (args.length == 0) {
            System.err.println("Usage: NTPClient <hostname-or-address-list>");
            System.exit(1);
        }

        NTPUDPClient client = new NTPUDPClient();
        // We want to timeout if a response takes longer than 10 seconds
        client.setDefaultTimeout(10000);
        try {
            client.open();
            for (int i = 0; i < args.length; i++)
            {
                System.out.println();
                try {
                    InetAddress hostAddr = InetAddress.getByName(args[i]);
                    System.out.println("> " + hostAddr.getHostName() + "/" + hostAddr.getHostAddress());
                    TimeInfo info = client.getTime(hostAddr);
                    processResponse(info);
                } catch (IOException ioe) {
                    ioe.printStackTrace();
                }
            }
        } catch (SocketException e) {
            e.printStackTrace();
        }

        client.close();
    }

}