如何使用互联网时间服务器来获得时间？
我想获得GMT [格林威治标准时间]，也不想依靠我的系统date时间。 基本上，我想使用时间同步服务器，如格林尼治标准时间计算in.pool.ntp.org [印度]，或者可能是我走错了方向！
如何在java中做到这一点？
有没有任何Java库来从时间服务器获得时间？
sp0d不太正确：
timeInfo.getReturnTime(); // Returns time at which time message packet was received by local machine 所以它只是返回当前的系统时间 ，而不是接收到的。 请参阅TimeInfo手册页 。
你应该使用
timeInfo.getMessage().getTransmitTimeStamp().getTime();
代替。
所以代码块将是：
String TIME_SERVER = "time-a.nist.gov"; NTPUDPClient timeClient = new NTPUDPClient(); InetAddress inetAddress = InetAddress.getByName(TIME_SERVER); TimeInfo timeInfo = timeClient.getTime(inetAddress); long returnTime = timeInfo.getMessage().getTransmitTimeStamp().getTime(); Date time = new Date(returnTime);
这是我find的其他代码..我正在使用它。
使用Apache公共库。
//时间服务器列表： http ： //tf.nist.gov/service/time-servers.html
import java.net.InetAddress; import java.util.Date; import org.apache.commons.net.ntp.NTPUDPClient; import org.apache.commons.net.ntp.TimeInfo; public class TimeLookup { public static void main() throws Exception { String TIME_SERVER = "time-a.nist.gov"; NTPUDPClient timeClient = new NTPUDPClient(); InetAddress inetAddress = InetAddress.getByName(TIME_SERVER); TimeInfo timeInfo = timeClient.getTime(inetAddress); long returnTime = timeInfo.getReturnTime(); Date time = new Date(returnTime); System.out.println("Time from " + TIME_SERVER + ": " + time); } }
从time-d.nist.gov返回输出时间：Sun Nov 25 06:04:34 IST 2012
这个链接演示了一个名为NtpMessage.java的java类，你可以将它粘贴到你的程序中，从NTP服务器获取当前时间。
在下面的链接中，find底部附近的“附件”部分，下载NtpMessage.java和SntpClient.java并将其粘贴到您的Java应用程序中。 它会做所有的工作，并把你的时间。
http://support.ntp.org/bin/view/Support/JavaSntpClient
复制并粘贴代码，如果它下降：
import java.text.DecimalFormat; import java.text.SimpleDateFormat; import java.util.Date; /** * This class represents a NTP message, as specified in RFC 2030. The message * format is compatible with all versions of NTP and SNTP. * * 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 */ 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 (eg, 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 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 + "\n" + "Version: " + version + "\n" + "Mode: " + mode + "\n" + "Stratum: " + stratum + "\n" + "Poll: " + pollInterval + "\n" + "Precision: " + precision + " (" + precisionStr + " seconds)\n" + "Root delay: " + new DecimalFormat("0.00").format(rootDelay*1000) + " ms\n" + "Root dispersion: " + new DecimalFormat("0.00").format(rootDispersion*1000) + " ms\n" + "Reference identifier: " + referenceIdentifierToString(referenceIdentifier, stratum, version) + "\n" + "Reference timestamp: " + timestampToString(referenceTimestamp) + "\n" + "Originate timestamp: " + timestampToString(originateTimestamp) + "\n" + "Receive timestamp: " + timestampToString(receiveTimestamp) + "\n" + "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 ""; } }
