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网站建设续费多少钱,软件商店下载安装2023版本最新,桂林户外论坛,网站关键词更换了网络时间协议#xff08;英语#xff1a;Network Time Protocol#xff0c;NTP#xff09;是以封包交换把两台电脑的时钟同步化的网络协议。NTP使用UDP端口123作为传输层。它是用作抵销可变延迟的影响。 NTP是仍在使用中的最古老的网络协议之一#xff08;在1985年前开始英语Network Time ProtocolNTP是以封包交换把两台电脑的时钟同步化的网络协议。NTP使用UDP端口123作为传输层。它是用作抵销可变延迟的影响。NTP是仍在使用中的最古老的网络协议之一在1985年前开始。NTP最初由德拉瓦州大学的Dave Mills设计他与一群志愿者仍在维护NTP。常用的NTP服务器中国国家授时中心 NTP 服务器服务器地址ntp.ntsc.ac.cnIP 地址202.120.2.101阿里云 NTP 服务器服务器地址ntp.aliyun.comIP 地址110.75.8.1腾讯云 NTP 服务器服务器地址time.tencentcloud.comIP 地址119.28.117.206华为云 NTP 服务器服务器地址time.hicloud.comIP 地址120.196.166.232两个类一个用于解析NTP消息另一个根据配置文件使用NTP协议获取时间。由于是JavaEE项目文件路径使用的ServletActionContext的路径。如果是一般Java项目写成配置所在路径即可。package com.geofly.mqtt; /** * author chenshixian **/ 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; import java.text.DecimalFormat; import java.text.SimpleDateFormat; import java.util.Date; public class NtpUtil { static String ntpServer ntp.ntsc.ac.cn; static Integer retry 3; static Integer port 123; static Integer timeout 3000; /** * 读取time.txt中的配置返回标准时间与本地时间的差值单位秒 * * return */ public static Double localClockOffset() { // get the address and NTP address request // InetAddress ipv4Addr null; try { ipv4Addr InetAddress.getByName(ntpServer);// 更多NTP时间服务器参考附注 } catch (UnknownHostException e1) { e1.printStackTrace(); } int serviceStatus -1; DatagramSocket socket null; long responseTime -1; double localClockOffset 0; 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; // 这里要加2208988800是因为获得到的时间是格林尼治时间所以要变成东八区的时间否则会与与北京时间有8小时的时差 // Validate NTP Response // IOException thrown if packet does not decode as expected. NtpMessage msg new NtpMessage(incoming.getData()); 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); // } return localClockOffset; } public static void main(String[] args) { localClockOffset(); } } 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. Its 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 codepointer/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 ; } }