Java tutorial
package com.amplify.gcm.hack; /* * 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 android.util.Log; import org.apache.commons.net.ntp.*; 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 * * @author Jason Mathews, MITRE Corp * * */ public final class NTPClient { private static final NumberFormat numberFormat = new java.text.DecimalFormat("0.00"); private static final String TAG = "GCM Demo"; private static long clockOffset; /** * 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. 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 + ")"; TimeStamp refNtpTime = message.getReferenceTimeStamp(); // Originate Time is time request sent by client (t1) TimeStamp origNtpTime = message.getOriginateTimeStamp(); long destTime = info.getReturnTime(); long localDestTime = System.currentTimeMillis(); // Receive Time is time request received by server (t2) TimeStamp rcvNtpTime = message.getReceiveTimeStamp(); // Transmit time is time reply sent by server (t3) TimeStamp xmitNtpTime = message.getTransmitTimeStamp(); // Destination time is time reply received by client (t4) TimeStamp destNtpTime = TimeStamp.getNtpTime(destTime); 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(); clockOffset = offsetValue != null ? offsetValue.longValue() : 0L; Log.i(TAG, " Reference Identifier:\t" + refAddr); Log.i(TAG, " Reference Timestamp:\t" + refNtpTime + " " + refNtpTime.toDateString()); Log.i(TAG, " Originate Timestamp:\t" + origNtpTime + " " + origNtpTime.toDateString()); Log.i(TAG, " Receive Timestamp:\t" + rcvNtpTime + " " + rcvNtpTime.toDateString()); Log.i(TAG, " Transmit Timestamp:\t" + xmitNtpTime + " " + xmitNtpTime.toDateString()); Log.i(TAG, " Destination Timestamp:\t" + destNtpTime + " " + destNtpTime.toDateString()); Log.i(TAG, " Roundtrip delay(ms)=" + delay + ", clock offset(ms)=" + offset); } public static void syncServerTime(String ntpServerAddress) throws IOException { NTPUDPClient client = new NTPUDPClient(); // We want to timeout if a response takes longer than 10 seconds client.setDefaultTimeout(10000); try { client.open(); System.out.println(); try { InetAddress hostAddr = InetAddress.getByName(ntpServerAddress); System.out.println("> " + hostAddr.getHostName() + "/" + hostAddr.getHostAddress()); TimeInfo info = client.getTime(hostAddr); processResponse(info); } catch (IOException ioe) { client.close(); throw ioe; } } catch (SocketException e) { client.close(); throw e; } client.close(); } public static Long getSyncedTime() { return System.currentTimeMillis() + clockOffset; } }