連接NTP服務器,查詢服務是否工作正常,或者取時間差來進行時間調整等........
import java.io.IOException;import java.io.InterruptedIOException;import java.net.ConnectException;import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import java.net.NoRouteToHostException;import java.net.UnknownHostException;
public class TestNtp {
public static void main(String[] args){
int retry = 2; int port = 123; int timeout = 3000; // get the address and NTP address request // InetAddress ipv4Addr = null; try { ipv4Addr = InetAddress.getByName("time.windows.com"); } catch (UnknownHostException e1) { e1.printStackTrace();
} int serviceStatus = -1; DatagramSocket socket = null; long responseTime = -1; try { socket = new DatagramSocket(); socket.setSoTimeout(timeout); // will force the // InterruptedIOException for (int attempts = 0; attempts <= retry && serviceStatus != 1; attempts++) { try { // Send NTP request // byte[] data = new NtpMessage().toByteArray(); DatagramPacket outgoing = new DatagramPacket(data, data.length, ipv4Addr, port); long sentTime = System.currentTimeMillis(); socket.send(outgoing); // Get NTP Response // // byte[] buffer = new byte[512]; DatagramPacket incoming = new DatagramPacket(data, data.length); socket.receive(incoming); responseTime = System.currentTimeMillis() - sentTime; double destinationTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0; // Validate NTP Response // IOException thrown if packet does not decode as expected. NtpMessage msg = new NtpMessage(incoming.getData()); double localClockOffset = ((msg.receiveTimestamp - msg.originateTimestamp) + (msg.transmitTimestamp - destinationTimestamp)) / 2; System.out.println("poll: valid NTP request received the local clock offset is " + localClockOffset + ", responseTime= " + responseTime + "ms"); System.out.println("poll: NTP message : " + msg.toString()); serviceStatus = 1; } catch (InterruptedIOException ex) { // Ignore, no response received. } } } catch (NoRouteToHostException e) { System.out.println("No route to host exception for address: " + ipv4Addr); } catch (ConnectException e) { // Connection refused. Continue to retry. e.fillInStackTrace(); System.out.println("Connection exception for address: " + ipv4Addr); } catch (IOException ex) { ex.fillInStackTrace(); System.out.println("IOException while polling address: " + ipv4Addr); } finally { if (socket != null) socket.close(); } // Store response time if available // if (serviceStatus == 1) { System.out.println("responsetime=="+responseTime); } }
}/** * This class represents a NTP message, as specified in RFC 2030. The message * format is compatible with all versions of NTP and SNTP. ToDo: Is this true? * * This class does not support the optional authentication protocol, and * ignores the key ID and message digest fields. * * For convenience, this class exposes message values as native Java types, not * the NTP-specified data formats. For example, timestamps are * stored as doubles (as opposed to the NTP unsigned 64-bit fixed point * format). * * However, the contructor NtpMessage(byte[]) and the method toByteArray() * allow the import and export of the raw NTP message format. * * * Usage example * * // Send message * DatagramSocket socket = new DatagramSocket(); * InetAddress address = InetAddress.getByName("ntp.cais.rnp.br"); * byte[] buf = new NtpMessage().toByteArray(); * DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 123); * socket.send(packet); * * // Get response * socket.receive(packet); * System.out.println(msg.toString()); * * * This code is copyright (c) Adam Buckley 2004 * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License as published by the Free * Software Foundation; either version 2 of the License, or (at your option) * any later version. A HTML version of the GNU General Public License can be * seen at http://www.gnu.org/licenses/gpl.html * * This program is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for * more details. * * * Comments for member variables are taken from RFC2030 by David Mills, * University of Delaware. * * Number format conversion code in NtpMessage(byte[] array) and toByteArray() * inspired by http://www.pps.jussieu.fr/~jch/enseignement/reseaux/ * NTPMessage.java which is copyright (c) 2003 by Juliusz Chroboczek * * @author Adam Buckley */import java.text.DecimalFormat;import java.text.SimpleDateFormat;import java.util.Date;public class NtpMessage { /** * This is a two-bit code warning of an impending leap second to be * inserted/deleted in the last minute of the current day. It's values may * be as follows: * * Value Meaning ----- ------- 0 no warning 1 last minute has 61 seconds 2 * last minute has 59 seconds) 3 alarm condition (clock not synchronized) */ public byte leapIndicator = 0; /** * This value indicates the NTP/SNTP version number. The version number is 3 * for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI). If * necessary to distinguish between IPv4, IPv6 and OSI, the encapsulating * context must be inspected. */ public byte version = 3; /** * This value indicates the mode, with values defined as follows: * * Mode Meaning ---- ------- 0 reserved 1 symmetric active 2 symmetric * passive 3 client 4 server 5 broadcast 6 reserved for NTP control message * 7 reserved for private use * * In unicast and anycast modes, the client sets this field to 3 (client) in * the request and the server sets it to 4 (server) in the reply. In * multicast mode, the server sets this field to 5 (broadcast). */ public byte mode = 0; /** * This value indicates the stratum level of the local clock, with values * defined as follows: * * Stratum Meaning ---------------------------------------------- 0 * unspecified or unavailable 1 primary reference (e.g., radio clock) 2-15 * secondary reference (via NTP or SNTP) 16-255 reserved */ public short stratum = 0; /** * This value indicates the maximum interval between successive messages, in * seconds to the nearest power of two. The values that can appear in this * field presently range from 4 (16 s) to 14 (16284 s); however, most * applications use only the sub-range 6 (64 s) to 10 (1024 s). */ public byte pollInterval = 0; /** * This value indicates the precision of the local clock, in seconds to the * nearest power of two. The values that normally appear in this field * range from -6 for mains-frequency clocks to -20 for microsecond clocks * found in some workstations. */ public byte precision = 0; /** * This value indicates the total roundtrip delay to the primary reference * source, in seconds. Note that this variable can take on both positive and * negative values, depending on the relative time and frequency offsets. * The values that normally appear in this field range from negative values * of a few milliseconds to positive values of several hundred milliseconds. */ public double rootDelay = 0; /** * This value indicates the nominal error relative to the primary reference * source, in seconds. The values that normally appear in this field range * from 0 to several hundred milliseconds. */ public double rootDispersion = 0; /** * This is a 4-byte array identifying the particular reference source. In * the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or * stratum-1 (primary) servers, this is a four-character ASCII string, left * justified and zero padded to 32 bits. In NTP Version 3 secondary servers, * this is the 32-bit IPv4 address of the reference source. In NTP Version 4 * secondary servers, this is the low order 32 bits of the latest transmit * timestamp of the reference source. NTP primary (stratum 1) servers should * set this field to a code identifying the external reference source * according to the following list. If the external reference is one of * those listed, the associated code should be used. Codes for sources not * listed can be contrived as appropriate. * * Code External Reference Source ---- ------------------------- LOCL * uncalibrated local clock used as a primary reference for a subnet without * external means of synchronization PPS atomic clock or other * pulse-per-second source individually calibrated to national standards * ACTS NIST dialup modem service USNO USNO modem service PTB PTB (Germany) * modem service TDF Allouis (France) Radio 164 kHz DCF Mainflingen * (Germany) Radio 77.5 kHz MSF Rugby (UK) Radio 60 kHz WWV Ft. Collins (US) * Radio 2.5, 5, 10, 15, 20 MHz WWVB Boulder (US) Radio 60 kHz WWVH Kaui * Hawaii (US) Radio 2.5, 5, 10, 15 MHz CHU Ottawa (Canada) Radio 3330, * 7335, 14670 kHz LORC LORAN-C radionavigation system OMEG OMEGA * radionavigation system GPS Global Positioning Service GOES Geostationary * Orbit Environment Satellite */ public byte[] referenceIdentifier = { 0, 0, 0, 0 }; /** * This is the time at which the local clock was last set or corrected, in * seconds since 00:00 1-Jan-1900. */ public double referenceTimestamp = 0; /** * This is the time at which the request departed the client for the server, * in seconds since 00:00 1-Jan-1900. */ public double originateTimestamp = 0; /** * This is the time at which the request arrived at the server, in seconds * since 00:00 1-Jan-1900. */ public double receiveTimestamp = 0; /** * This is the time at which the reply departed the server for the client, * in seconds since 00:00 1-Jan-1900. */ public double transmitTimestamp = 0; /** * Constructs a new NtpMessage from an array of bytes. */ public NtpMessage(byte[] array) { // See the packet format diagram in RFC 2030 for details leapIndicator = (byte) ((array[0] >> 6) & 0x3); version = (byte) ((array[0] >> 3) & 0x7); mode = (byte) (array[0] & 0x7); stratum = unsignedByteToShort(array[1]); pollInterval = array[2]; precision = array[3]; rootDelay = (array[4] * 256.0) + unsignedByteToShort(array[5]) + (unsignedByteToShort(array[6]) / 256.0) + (unsignedByteToShort(array[7]) / 65536.0); rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + unsignedByteToShort(array[9]) + (unsignedByteToShort(array[10]) / 256.0) + (unsignedByteToShort(array[11]) / 65536.0); referenceIdentifier[0] = array[12]; referenceIdentifier[1] = array[13]; referenceIdentifier[2] = array[14]; referenceIdentifier[3] = array[15]; referenceTimestamp = decodeTimestamp(array, 16); originateTimestamp = decodeTimestamp(array, 24); receiveTimestamp = decodeTimestamp(array, 32); transmitTimestamp = decodeTimestamp(array, 40); } /** * Constructs a new NtpMessage */ public NtpMessage(byte leapIndicator, byte version, byte mode, short stratum, byte pollInterval, byte precision, double rootDelay, double rootDispersion, byte[] referenceIdentifier, double referenceTimestamp, double originateTimestamp, double receiveTimestamp, double transmitTimestamp) { // ToDo: Validity checking this.leapIndicator = leapIndicator; this.version = version; this.mode = mode; this.stratum = stratum; this.pollInterval = pollInterval; this.precision = precision; this.rootDelay = rootDelay; this.rootDispersion = rootDispersion; this.referenceIdentifier = referenceIdentifier; this.referenceTimestamp = referenceTimestamp; this.originateTimestamp = originateTimestamp; this.receiveTimestamp = receiveTimestamp; this.transmitTimestamp = transmitTimestamp; } /** * Constructs a new NtpMessage in client -> server mode, and sets the * transmit timestamp to the current time. */ public NtpMessage() { // Note that all the other member variables are already set with // appropriate default values. this.mode = 3; this.transmitTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0; } /** * This method constructs the data bytes of a raw NTP packet. */ public byte[] toByteArray() { // All bytes are automatically set to 0 byte[] p = new byte[48]; p[0] = (byte) (leapIndicator << 6 | version << 3 | mode); p[1] = (byte) stratum; p[2] = (byte) pollInterval; p[3] = (byte) precision; // root delay is a signed 16.16-bit FP, in Java an int is 32-bits int l = (int) (rootDelay * 65536.0); p[4] = (byte) ((l >> 24) & 0xFF); p[5] = (byte) ((l >> 16) & 0xFF); p[6] = (byte) ((l >> 8) & 0xFF); p[7] = (byte) (l & 0xFF); // root dispersion is an unsigned 16.16-bit FP, in Java there are no // unsigned primitive types, so we use a long which is 64-bits long ul = (long) (rootDispersion * 65536.0); p[8] = (byte) ((ul >> 24) & 0xFF); p[9] = (byte) ((ul >> 16) & 0xFF); p[10] = (byte) ((ul >> 8) & 0xFF); p[11] = (byte) (ul & 0xFF); p[12] = referenceIdentifier[0]; p[13] = referenceIdentifier[1]; p[14] = referenceIdentifier[2]; p[15] = referenceIdentifier[3]; encodeTimestamp(p, 16, referenceTimestamp); encodeTimestamp(p, 24, originateTimestamp); encodeTimestamp(p, 32, receiveTimestamp); encodeTimestamp(p, 40, transmitTimestamp); return p; } /** * Returns a string representation of a NtpMessage */ public String toString() { String precisionStr = new DecimalFormat("0.#E0").format(Math.pow(2, precision)); return "Leap indicator: " + leapIndicator + " " + "Version: " + version + " " + "Mode: " + mode + " " + "Stratum: " + stratum + " " + "Poll: " + pollInterval + " " + "Precision: " + precision + " (" + precisionStr + " seconds) " + "Root delay: " + new DecimalFormat("0.00").format(rootDelay * 1000) + " ms " + "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion * 1000) + " ms " + "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + " " + "Reference timestamp: " + timestampToString(referenceTimestamp) + " " + "Originate timestamp: " + timestampToString(originateTimestamp) + " " + "Receive timestamp: " + timestampToString(receiveTimestamp) + " " + "Transmit timestamp: " + timestampToString(transmitTimestamp); } /** * Converts an unsigned byte to a short. By default, Java assumes that a * byte is signed. */ public static short unsignedByteToShort(byte b) { if ((b & 0x80) == 0x80) return (short) (128 + (b & 0x7f)); else return (short) b; } /** * Will read 8 bytes of a message beginning at <code>pointer</code> and * return it as a double, according to the NTP 64-bit timestamp format. */ public static double decodeTimestamp(byte[] array, int pointer) { double r = 0.0; for (int i = 0; i < 8; i++) { r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8); } return r; } /** * Encodes a timestamp in the specified position in the message */ public static void encodeTimestamp(byte[] array, int pointer, double timestamp) { // Converts a double into a 64-bit fixed point for (int i = 0; i < 8; i++) { // 2^24, 2^16, 2^8, .. 2^-32 double base = Math.pow(2, (3 - i) * 8); // Capture byte value array[pointer + i] = (byte) (timestamp / base); // Subtract captured value from remaining total timestamp = timestamp - (double) (unsignedByteToShort(array[pointer + i]) * base); } // From RFC 2030: It is advisable to fill the non-significant // low order bits of the timestamp with a random, unbiased // bitstring, both to avoid systematic roundoff errors and as // a means of loop detection and replay detection. array[7] = (byte) (Math.random() * 255.0); } /** * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a * formatted date/time string. */ public static String timestampToString(double timestamp) { if (timestamp == 0) return "0"; // timestamp is relative to 1900, utc is used by Java and is relative // to 1970 double utc = timestamp - (2208988800.0); // milliseconds long ms = (long) (utc * 1000.0); // date/time String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms)); // fraction double fraction = timestamp - ((long) timestamp); String fractionSting = new DecimalFormat(".000000").format(fraction); return date + fractionSting; } /** * Returns a string representation of a reference identifier according to * the rules set out in RFC 2030. */ public static String referenceIdentifierToString(byte[] ref, short stratum, byte version) { // From the RFC 2030: // In the case of NTP Version 3 or Version 4 stratum-0 (unspecified) // or stratum-1 (primary) servers, this is a four-character ASCII // string, left justified and zero padded to 32 bits. if (stratum == 0 || stratum == 1) { return new String(ref); } // In NTP Version 3 secondary servers, this is the 32-bit IPv4 // address of the reference source. else if (version == 3) { return unsignedByteToShort(ref[0]) + "." + unsignedByteToShort(ref[1]) + "." + unsignedByteToShort(ref[2]) + "." + unsignedByteToShort(ref[3]); } // In NTP Version 4 secondary servers, this is the low order 32 bits // of the latest transmit timestamp of the reference source. else if (version == 4) { return "" + ((unsignedByteToShort(ref[0]) / 256.0) + (unsignedByteToShort(ref[1]) / 65536.0) + (unsignedByteToShort(ref[2]) / 16777216.0) + (unsignedByteToShort(ref[3]) / 4294967296.0)); } return ""; }}