网络时间同步

从NTP服务器获取时间同步客户端：

 1 import java.io.IOException;
 2 import java.io.InterruptedIOException;
 3 import java.net.ConnectException;
 4 import java.net.DatagramPacket;
 5 import java.net.DatagramSocket;
 6 import java.net.InetAddress;
 7 import java.net.NoRouteToHostException;
 8 import java.net.UnknownHostException;
 9 
10 public class TestNtp{
11 
12     public static void main(String[] args){
13         int retry = 2;
14         int port = 123;
15         int timeout = 3000;
16 
17         // get the address and NTP address request
18         //
19         InetAddress ipv4Addr = null;
20         try {
21             ipv4Addr = InetAddress.getByName("203.117.180.36");//更多NTP时间服务器参考附注
22                } catch (UnknownHostException e1) {
23             e1.printStackTrace();
24         }
25 
26         int serviceStatus = -1;
27         DatagramSocket socket = null;
28         long responseTime = -1;
29         try {
30             socket = new DatagramSocket();
31             socket.setSoTimeout(timeout); // will force the
32             // InterruptedIOException
33 
34             for (int attempts = 0; attempts <= retry && serviceStatus != 1; attempts++) {
35                 try {
36                     // Send NTP request
37                     //
38                     byte[] data = new NtpMessage().toByteArray();
39                     DatagramPacket outgoing = new DatagramPacket(data, data.length, ipv4Addr, port);
40                     long sentTime = System.currentTimeMillis();
41                     socket.send(outgoing);
42 
43                     // Get NTP Response
44                     //
45                     // byte[] buffer = new byte[512];
46                     DatagramPacket incoming = new DatagramPacket(data, data.length);
47                     socket.receive(incoming);
48                     responseTime = System.currentTimeMillis() - sentTime;
49                     double destinationTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0;
50                     //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
51 
52                     // Validate NTP Response
53                     // IOException thrown if packet does not decode as expected.
54                     NtpMessage msg = new NtpMessage(incoming.getData());
55                     double localClockOffset = ((msg.receiveTimestamp - msg.originateTimestamp) + (msg.transmitTimestamp - destinationTimestamp)) / 2;
56 
57                     System.out.println("poll: valid NTP request received the local clock offset is " + localClockOffset + ", responseTime= " + responseTime + "ms");
58                     System.out.println("poll: NTP message : " + msg.toString());
59                     serviceStatus = 1;
60                 } catch (InterruptedIOException ex) {
61                     // Ignore, no response received.
62                 }
63             }
64         } catch (NoRouteToHostException e) {
65             System.out.println("No route to host exception for address: " + ipv4Addr);
66         } catch (ConnectException e) {
67             // Connection refused. Continue to retry.
68             e.fillInStackTrace();
69             System.out.println("Connection exception for address: " + ipv4Addr);
70         } catch (IOException ex) {
71             ex.fillInStackTrace();
72             System.out.println("IOException while polling address: " + ipv4Addr);
73         } finally {
74             if (socket != null)
75                 socket.close();
76         }
77 
78         // Store response time if available
79         //
80         if (serviceStatus == 1) {
81             System.out.println("responsetime=="+responseTime);
82         }
83 
84         
85     }
86 }

View Code

协议解析模型

  1 import java.text.DecimalFormat;
  2 import java.text.SimpleDateFormat;
  3 import java.util.Date;
  4 
  5 public class NtpMessage {
  6     /** *//**
  7      * This is a two-bit code warning of an impending leap second to be
  8      * inserted/deleted in the last minute of the current day. It''s values may
  9      * be as follows:
 10      * 
 11      * Value Meaning ----- ------- 0 no warning 1 last minute has 61 seconds 2
 12      * last minute has 59 seconds) 3 alarm condition (clock not synchronized)
 13      */
 14     public byte leapIndicator = 0;
 15 
 16     /** *//**
 17      * This value indicates the NTP/SNTP version number. The version number is 3
 18      * for Version 3 (IPv4 only) and 4 for Version 4 (IPv4, IPv6 and OSI). If
 19      * necessary to distinguish between IPv4, IPv6 and OSI, the encapsulating
 20      * context must be inspected.
 21      */
 22     public byte version = 3;
 23 
 24     /** *//**
 25      * This value indicates the mode, with values defined as follows:
 26      * 
 27      * Mode Meaning ---- ------- 0 reserved 1 symmetric active 2 symmetric
 28      * passive 3 client 4 server 5 broadcast 6 reserved for NTP control message
 29      * 7 reserved for private use
 30      * 
 31      * In unicast and anycast modes, the client sets this field to 3 (client) in
 32      * the request and the server sets it to 4 (server) in the reply. In
 33      * multicast mode, the server sets this field to 5 (broadcast).
 34      */
 35     public byte mode = 0;
 36 
 37     /** *//**
 38      * This value indicates the stratum level of the local clock, with values
 39      * defined as follows:
 40      * 
 41      * Stratum Meaning ---------------------------------------------- 0
 42      * unspecified or unavailable 1 primary reference (e.g., radio clock) 2-15
 43      * secondary reference (via NTP or SNTP) 16-255 reserved
 44      */
 45     public short stratum = 0;
 46 
 47     /** *//**
 48      * This value indicates the maximum interval between successive messages, in
 49      * seconds to the nearest power of two. The values that can appear in this
 50      * field presently range from 4 (16 s) to 14 (16284 s); however, most
 51      * applications use only the sub-range 6 (64 s) to 10 (1024 s).
 52      */
 53     public byte pollInterval = 0;
 54 
 55     /** *//**
 56      * This value indicates the precision of the local clock, in seconds to the
 57      * nearest power of two. The values that normally appear in this field
 58      * range from -6 for mains-frequency clocks to -20 for microsecond clocks
 59      * found in some workstations.
 60      */
 61     public byte precision = 0;
 62 
 63     /** *//**
 64      * This value indicates the total roundtrip delay to the primary reference
 65      * source, in seconds. Note that this variable can take on both positive and
 66      * negative values, depending on the relative time and frequency offsets.
 67      * The values that normally appear in this field range from negative values
 68      * of a few milliseconds to positive values of several hundred milliseconds.
 69      */
 70     public double rootDelay = 0;
 71 
 72     /** *//**
 73      * This value indicates the nominal error relative to the primary reference
 74      * source, in seconds. The values that normally appear in this field range
 75      * from 0 to several hundred milliseconds.
 76      */
 77     public double rootDispersion = 0;
 78 
 79     /** *//**
 80      * This is a 4-byte array identifying the particular reference source. In
 81      * the case of NTP Version 3 or Version 4 stratum-0 (unspecified) or
 82      * stratum-1 (primary) servers, this is a four-character ASCII string, left
 83      * justified and zero padded to 32 bits. In NTP Version 3 secondary servers,
 84      * this is the 32-bit IPv4 address of the reference source. In NTP Version 4
 85      * secondary servers, this is the low order 32 bits of the latest transmit
 86      * timestamp of the reference source. NTP primary (stratum 1) servers should
 87      * set this field to a code identifying the external reference source
 88      * according to the following list. If the external reference is one of
 89      * those listed, the associated code should be used. Codes for sources not
 90      * listed can be contrived as appropriate.
 91      * 
 92      * Code External Reference Source ---- ------------------------- LOCL
 93      * uncalibrated local clock used as a primary reference for a subnet without
 94      * external means of synchronization PPS atomic clock or other
 95      * pulse-per-second source individually calibrated to national standards
 96      * ACTS NIST dialup modem service USNO USNO modem service PTB PTB (Germany)
 97      * modem service TDF Allouis (France) Radio 164 kHz DCF Mainflingen
 98      * (Germany) Radio 77.5 kHz MSF Rugby (UK) Radio 60 kHz WWV Ft. Collins (US)
 99      * Radio 2.5, 5, 10, 15, 20 MHz WWVB Boulder (US) Radio 60 kHz WWVH Kaui
100      * Hawaii (US) Radio 2.5, 5, 10, 15 MHz CHU Ottawa (Canada) Radio 3330,
101      * 7335, 14670 kHz LORC LORAN-C radionavigation system OMEG OMEGA
102      * radionavigation system GPS Global Positioning Service GOES Geostationary
103      * Orbit Environment Satellite
104      */
105     public byte[] referenceIdentifier = { 0, 0, 0, 0 };
106 
107     /** *//**
108      * This is the time at which the local clock was last set or corrected, in
109      * seconds since 00:00 1-Jan-1900.
110      */
111     public double referenceTimestamp = 0;
112 
113     /** *//**
114      * This is the time at which the request departed the client for the server,
115      * in seconds since 00:00 1-Jan-1900.
116      */
117     public double originateTimestamp = 0;
118 
119     /** *//**
120      * This is the time at which the request arrived at the server, in seconds
121      * since 00:00 1-Jan-1900.
122      */
123     public double receiveTimestamp = 0;
124 
125     /** *//**
126      * This is the time at which the reply departed the server for the client,
127      * in seconds since 00:00 1-Jan-1900.
128      */
129     public double transmitTimestamp = 0;
130 
131     /** *//**
132      * Constructs a new NtpMessage from an array of bytes.
133      */
134     public NtpMessage(byte[] array) {
135         // See the packet format diagram in RFC 2030 for details
136         leapIndicator = (byte) ((array[0] >> 6) & 0x3);
137         version = (byte) ((array[0] >> 3) & 0x7);
138         mode = (byte) (array[0] & 0x7);
139         stratum = unsignedByteToShort(array[1]);
140         pollInterval = array[2];
141         precision = array[3];
142 
143         rootDelay = (array[4] * 256.0) + unsignedByteToShort(array[5]) + (unsignedByteToShort(array[6]) / 256.0) + (unsignedByteToShort(array[7]) / 65536.0);
144 
145         rootDispersion = (unsignedByteToShort(array[8]) * 256.0) + unsignedByteToShort(array[9]) + (unsignedByteToShort(array[10]) / 256.0) + (unsignedByteToShort(array[11]) / 65536.0);
146 
147         referenceIdentifier[0] = array[12];
148         referenceIdentifier[1] = array[13];
149         referenceIdentifier[2] = array[14];
150         referenceIdentifier[3] = array[15];
151 
152         referenceTimestamp = decodeTimestamp(array, 16);
153         originateTimestamp = decodeTimestamp(array, 24);
154         receiveTimestamp = decodeTimestamp(array, 32);
155         transmitTimestamp = decodeTimestamp(array, 40);
156     }
157 
158     /** *//**
159      * Constructs a new NtpMessage
160      */
161     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) {
162         // ToDo: Validity checking
163         this.leapIndicator = leapIndicator;
164         this.version = version;
165         this.mode = mode;
166         this.stratum = stratum;
167         this.pollInterval = pollInterval;
168         this.precision = precision;
169         this.rootDelay = rootDelay;
170         this.rootDispersion = rootDispersion;
171         this.referenceIdentifier = referenceIdentifier;
172         this.referenceTimestamp = referenceTimestamp;
173         this.originateTimestamp = originateTimestamp;
174         this.receiveTimestamp = receiveTimestamp;
175         this.transmitTimestamp = transmitTimestamp;
176     }
177 
178     /** *//**
179      * Constructs a new NtpMessage in client -> server mode, and sets the
180      * transmit timestamp to the current time.
181      */
182     public NtpMessage() {
183         // Note that all the other member variables are already set with
184         // appropriate default values.
185         this.mode = 3;
186         this.transmitTimestamp = (System.currentTimeMillis() / 1000.0) + 2208988800.0;
187     }
188 
189     /** *//**
190      * This method constructs the data bytes of a raw NTP packet.
191      */
192     public byte[] toByteArray() {
193         // All bytes are automatically set to 0
194         byte[] p = new byte[48];
195 
196         p[0] = (byte) (leapIndicator << 6 | version << 3 | mode);
197         p[1] = (byte) stratum;
198         p[2] = (byte) pollInterval;
199         p[3] = (byte) precision;
200 
201         // root delay is a signed 16.16-bit FP, in Java an int is 32-bits
202         int l = (int) (rootDelay * 65536.0);
203         p[4] = (byte) ((l >> 24) & 0xFF);
204         p[5] = (byte) ((l >> 16) & 0xFF);
205         p[6] = (byte) ((l >> 8) & 0xFF);
206         p[7] = (byte) (l & 0xFF);
207 
208         // root dispersion is an unsigned 16.16-bit FP, in Java there are no
209         // unsigned primitive types, so we use a long which is 64-bits
210         long ul = (long) (rootDispersion * 65536.0);
211         p[8] = (byte) ((ul >> 24) & 0xFF);
212         p[9] = (byte) ((ul >> 16) & 0xFF);
213         p[10] = (byte) ((ul >> 8) & 0xFF);
214         p[11] = (byte) (ul & 0xFF);
215 
216         p[12] = referenceIdentifier[0];
217         p[13] = referenceIdentifier[1];
218         p[14] = referenceIdentifier[2];
219         p[15] = referenceIdentifier[3];
220 
221         encodeTimestamp(p, 16, referenceTimestamp);
222         encodeTimestamp(p, 24, originateTimestamp);
223         encodeTimestamp(p, 32, receiveTimestamp);
224         encodeTimestamp(p, 40, transmitTimestamp);
225 
226         return p;
227     }
228 
229     /** *//**
230      * Returns a string representation of a NtpMessage
231      */
232     public String toString() {
233         String precisionStr = new DecimalFormat("0.#E0").format(Math.pow(2, precision));
234         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);
235     }
236 
237     /** *//**
238      * Converts an unsigned byte to a short. By default, Java assumes that a
239      * byte is signed.
240      */
241     public static short unsignedByteToShort(byte b) {
242         if ((b & 0x80) == 0x80)
243             return (short) (128 + (b & 0x7f));
244         else
245             return (short) b;
246     }
247 
248     /** *//**
249      * Will read 8 bytes of a message beginning at pointer and
250      * return it as a double, according to the NTP 64-bit timestamp format.
251      */
252     public static double decodeTimestamp(byte[] array, int pointer) {
253         double r = 0.0;
254 
255         for (int i = 0; i < 8; i++) {
256             r += unsignedByteToShort(array[pointer + i]) * Math.pow(2, (3 - i) * 8);
257         }
258 
259         return r;
260     }
261 
262     /** *//**
263      * Encodes a timestamp in the specified position in the message
264      */
265     public static void encodeTimestamp(byte[] array, int pointer, double timestamp) {
266         // Converts a double into a 64-bit fixed point
267         for (int i = 0; i < 8; i++) {
268             // 2^24, 2^16, 2^8, .. 2^-32
269             double base = Math.pow(2, (3 - i) * 8);
270 
271             // Capture byte value
272             array[pointer + i] = (byte) (timestamp / base);
273 
274             // Subtract captured value from remaining total
275             timestamp = timestamp - (double) (unsignedByteToShort(array[pointer + i]) * base);
276         }
277 
278         // From RFC 2030: It is advisable to fill the non-significant
279         // low order bits of the timestamp with a random, unbiased
280         // bitstring, both to avoid systematic roundoff errors and as
281         // a means of loop detection and replay detection.
282         array[7] = (byte) (Math.random() * 255.0);
283     }
284 
285     /** *//**
286      * Returns a timestamp (number of seconds since 00:00 1-Jan-1900) as a
287      * formatted date/time string.
288      */
289     public static String timestampToString(double timestamp) {
290         if (timestamp == 0)
291             return "0";
292 
293         // timestamp is relative to 1900, utc is used by Java and is relative
294         // to 1970
295         double utc = timestamp - (2208988800.0);
296 
297         // milliseconds
298         long ms = (long) (utc * 1000.0);
299 
300         // date/time
301         String date = new SimpleDateFormat("dd-MMM-yyyy HH:mm:ss").format(new Date(ms));
302 
303         // fraction
304         double fraction = timestamp - ((long) timestamp);
305         String fractionSting = new DecimalFormat(".000000").format(fraction);
306 
307         return date + fractionSting;
308     }
309 
310     /** *//**
311      * Returns a string representation of a reference identifier according to
312      * the rules set out in RFC 2030.
313      */
314     public static String referenceIdentifierToString(byte[] ref, short stratum, byte version) {
315         // From the RFC 2030:
316         // In the case of NTP Version 3 or Version 4 stratum-0 (unspecified)
317         // or stratum-1 (primary) servers, this is a four-character ASCII
318         // string, left justified and zero padded to 32 bits.
319         if (stratum == 0 || stratum == 1) {
320             return new String(ref);
321         }
322 
323         // In NTP Version 3 secondary servers, this is the 32-bit IPv4
324         // address of the reference source.
325         else if (version == 3) {
326             return unsignedByteToShort(ref[0]) + "." + unsignedByteToShort(ref[1]) + "." + unsignedByteToShort(ref[2]) + "." + unsignedByteToShort(ref[3]);
327         }
328 
329         // In NTP Version 4 secondary servers, this is the low order 32 bits
330         // of the latest transmit timestamp of the reference source.
331         else if (version == 4) {
332             return "" + ((unsignedByteToShort(ref[0]) / 256.0) + (unsignedByteToShort(ref[1]) / 65536.0) + (unsignedByteToShort(ref[2]) / 16777216.0) + (unsignedByteToShort(ref[3]) / 4294967296.0));
333         }
334 
335         return "";
336     }
337 }

View Code

结果：

poll: valid NTP request received the local clock offset is 3606.92320227623, responseTime= 265ms
poll: NTP message : Leap indicator: 0 Version: 3 Mode: 4 Stratum: 1 Poll: 0 Precision: -18 (3.8E-6 seconds) Root delay: 0.00 ms Root dispersion: 0.00 ms Reference identifier: ACTS Reference timestamp: 26-三月-2009 20:50:23.508540 Originate timestamp: 26-三月-2009 19:51:10.031000 Receive timestamp:   26-三月-2009 20:51:17.086693 Transmit timestamp: 26-三月-2009 20:51:17.086712
responsetime==265

注意看红色部分，这是本地时间，我故意将本地时间调慢了一小时。


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。

 

转载于:https://www.cnblogs.com/isoftware/p/4480953.html