자바 NTP 타임 서버 를 통 해 시간 획득
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("203.117.180.36");// NTP
} 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;
// 2208988800， ， ， 8
// 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);
}
}
}
//**************************************************************************************************************
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 "";
}
}
결과:
poll: valid NTP request received the local clock offset is 3606.92320227623, responseTime= 265ms
poll:NTP message:Leap indicator:0 버 전: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:26-3 월-2009 20:50:23.508540 Originate timestamp:26-3 월-2009 19:51:10.31000 26-3 월-2009 20:51:17.086693 Transmit timestamp:26-3 월-2009 20:51:17.086712
responsetime==265
빨간색 부분 을 주의해 서 보 세 요.이것 은 현지 시간 입 니 다.저 는 일부러 현지 시간 을 한 시간 늦 추 었 습 니 다.
첨부 1:중국 에서 사용 할 수 있 는 NTP 시간 서버
server 133.100.11.8 prefer
server 210.72.145.44
server 203.117.180.36//프로그램 에 사 용 된
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(국가 시간 센터 서버 IP 주소)
ntpdate 131.107.1.10
ntpdate -s time.asia.apple.com
부주 2:NTP 개념 소개
Network Time Protocol(NTP)은 컴퓨터 시간 을 동기 화 하 는 프로 토 콜 입 니 다.컴퓨터 가 서버 나 시계 원본(예 를 들 어 석영 시계,GPS 등)을 동기 화 할 수 있 고 정확 한 시간 교정(LAN 과 표준 간 의 차 이 는 1 초,WAN 에서 몇 십 밀리초)을 제공 할 수 있 습 니 다.또한 암호 화 확인 방식 으로 악성 프로 토 콜 공격 을 방지 할 수 있 습 니 다.
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