Java tutorial
package com.cscao.apps.ntplib; /* * 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 org.apache.commons.net.ntp.NTPUDPClient; import org.apache.commons.net.ntp.NtpUtils; import org.apache.commons.net.ntp.NtpV3Packet; import org.apache.commons.net.ntp.TimeInfo; import org.apache.commons.net.ntp.TimeStamp; import java.io.IOException; import java.net.InetAddress; import java.net.SocketException; import java.net.UnknownHostException; import java.text.NumberFormat; /*** * 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 </A> * for details. * <p/> * Usage: NTPClient <hostname-or-address-list> * <br> * Example: NTPClient clock.psu.edu ***/ public final class NTPClient { private static final NumberFormat numberFormat = new java.text.DecimalFormat("0.00"); private int timeout; private String server; private String details = "Details: \n"; public NTPClient() { this(Constants.DEFAULT_SERVER, Constants.DEFAULT_TIMEOUT); } public NTPClient(String server) { this(server, Constants.DEFAULT_TIMEOUT); } public NTPClient(String server, int timeout) { this.server = server; this.timeout = timeout; } /** * Process <code>TimeInfo</code> object and print its details and return the offset. * * @param info <code>TimeInfo</code> object. */ private long processResponse(TimeInfo info) { NtpV3Packet message = info.getMessage(); if (message == null) { return 0; } 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); details += " Stratum: " + stratum + " " + refType + "\n"; int version = message.getVersion(); int li = message.getLeapIndicator(); // System.out.println(" leap=" + li + ", version=" // + version + ", precision=" + message.getPrecision()); details += " leap=" + li + ", version=" + version + ", precision=" + message.getPrecision() + "\n"; details += " mode: " + message.getModeName() + " (" + message.getMode() + ")" + "\n"; // 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 + ")"); details += " poll: " + (poll <= 0 ? 1 : (int) Math.pow(2, poll)) + " seconds" + " (2 ** " + poll + ")" + "\n"; double disp = message.getRootDispersionInMillisDouble(); // System.out.println(" rootdelay=" + numberFormat.format(message.getRootDelayInMillisDouble()) // + ", rootdispersion(ms): " + numberFormat.format(disp)); details += " rootdelay=" + numberFormat.format(message.getRootDelayInMillisDouble()) + ", rootdispersion(ms): " + numberFormat.format(disp) + "\n"; 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); details += " Reference Identifier:\t" + refAddr + "\n"; TimeStamp refNtpTime = message.getReferenceTimeStamp(); // System.out.println(" Reference Timestamp:\t" + refNtpTime + " " + refNtpTime.toDateString()); details += " Reference Timestamp:\t" + refNtpTime + " " + refNtpTime.toDateString() + "\n"; // Originate Time is time request sent by client (t1) TimeStamp origNtpTime = message.getOriginateTimeStamp(); // System.out.println(" Originate Timestamp:\t" + origNtpTime + " " + origNtpTime.toDateString()); details += " Originate Timestamp:\t" + origNtpTime + " " + origNtpTime.toDateString() + "\n"; 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()); details += " Receive Timestamp:\t" + rcvNtpTime + " " + rcvNtpTime.toDateString() + "\n"; // Transmit time is time reply sent by server (t3) TimeStamp xmitNtpTime = message.getTransmitTimeStamp(); // System.out.println(" Transmit Timestamp:\t" + xmitNtpTime + " " + xmitNtpTime.toDateString()); details += " Transmit Timestamp:\t" + xmitNtpTime + " " + xmitNtpTime.toDateString() + "\n"; // Destination time is time reply received by client (t4) TimeStamp destNtpTime = TimeStamp.getNtpTime(destTime); // System.out.println(" Destination Timestamp:\t" + destNtpTime + " " + destNtpTime.toDateString()); details += " Destination Timestamp:\t" + destNtpTime + " " + destNtpTime.toDateString() + "\n"; 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 details += " Roundtrip delay(ms)=" + delay + ", clock offset(ms)=" + offset + "\n"; // calibrate local clock // return (offsetValue == null) ? -1 : (destNtpTime.getTime() + offsetValue); // return offset return (offsetValue == null) ? 0 : offsetValue; } private TimeInfo requestTime(String server, int timeout) { TimeInfo responseInfo = null; NTPUDPClient client = new NTPUDPClient(); client.setDefaultTimeout(timeout); try { client.open(); try { InetAddress hostAddr = InetAddress.getByName(server); // System.out.println("> " + hostAddr.getHostName() + "/" // + hostAddr.getHostAddress()); details += "NTP server: " + hostAddr.getHostName() + "/" + hostAddr.getHostAddress(); responseInfo = client.getTime(hostAddr); } catch (IOException ioe) { ioe.printStackTrace(); } } catch (SocketException e) { e.printStackTrace(); } client.close(); return responseInfo; } public long getOffset() { TimeInfo info = requestTime(server, timeout); return processResponse(info); } public void setTimeout(int timeout) { this.timeout = timeout; } public void setServer(String server) { this.server = server; } public String getDetails() { return details; } public static void main(String[] args) { // if (args.length == 0) { // System.err.println("Usage: NTPClient <hostname-or-address-list>"); // System.exit(1); // } } }