NTP测试
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.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;/*** * This is an example program demonstrating how to use the NTPUDPClient 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 ** @author Jason Mathews, MITRE Corp ***/public final class NTPClient {private static final NumberFormat numberFormat = new java.text.DecimalFormat("0.00");/** * Process <code>TimeInfo</code> object and print its details. ** @param info * <code>TimeInfo</code> 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.elserefType = "(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 doneLong 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 == null || 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 secondsclient.setDefaultTimeout(10000);try {client.open();for (int i = 0; i < args.length; i++) {System.out.println();try {InetAddress hostAddr = InetAddress.getByName(args);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();}}参数可以在下面选择一个，我测试时候用的是ntp.nasa.gov，
测试结果：
> ntp.nasa.gov/198.123.30.132
Stratum: 1 (Primary Reference; e.g., GPS)
leap=0, version=3, precision=-16
mode: Server (4)
poll: 8 seconds (2 ** 3)
rootdelay=0.00, rootdispersion(ms): 0.85
Reference Identifier:71.80.83.0 (GPS)
Reference Timestamp:d0e3a8ae.7dee6367Fri, Jan 21 2011 14:39:42.492
Originate Timestamp:d0e3a851.9ced9168Fri, Jan 21 2011 14:38:09.613
Receive Timestamp:d0e3a8c6.485327f3Fri, Jan 21 2011 14:40:06.283
Transmit Timestamp:d0e3a8c6.4856fb74Fri, Jan 21 2011 14:40:06.283
Destination Timestamp:d0e3a852.16041893Fri, Jan 21 2011 14:38:10.086
Roundtrip delay(ms)=473, clock offset(ms)=116433
附注1：中国大概能用的NTP时间服务器
server 133.100.11.8 prefer
server 210.72.145.44
server 203.117.180.36 //程序中所用的
server 131.107.1.10
server time.asia.apple.com
server 64.236.96.53
server 130.149.17.21
server 66.92.68.246
server www.freebsd.org
server 18.145.0.30
server clock.via.net
server 137.92.140.80
server 133.100.9.2
server 128.118.46.3
server ntp.nasa.gov
server 129.7.1.66
server ntp-sop.inria.frserver 210.72.145.44(国家授时中心服务器IP地址)
ntpdate 131.107.1.10
ntpdate -s time.asia.apple.com
附注2：NTP概念简介
Network Time Protocol（NTP）是用来使计算机时间同步化的一种协议，它可以使计算机对其服务器或时钟源（如石英钟，GPS等等)做同步化，它可以提供高精准度的时间校正（LAN上与标准间差小于1毫秒，WAN上几十毫秒），且可介由加密确认的方式来防止恶毒的协议攻击。
部分参考自：
http://lshh83.iteye.com/blog/546405
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