最近在做一个应用,涉及到数据上报,数据上报就涉及到时间,如果时间不对,服务器可能会拒绝你的数据。就算不拒绝,你上报的数据也是不正确的,我们采取的是宁可不要数据,也用错误的数据。这就体现到NTP获取数据的重要性了。
但是查询了大半天,发现网上的ntp请求都是过时的,获取格式不正确,很难读懂。自己重新弄了一下,就记录下来以防以后在用到查询。
一、可用的NTP地址
"ntp1.aliyun.com, ntp2.aliyun.com, ntp3.aliyun.com, ntp4.aliyun.com, ntp5.aliyun.com, ntp6.aliyun.com, ntp7.aliyun.com,cn.pool.ntp.org, cn.ntp.org.cn, sg.pool.ntp.org, tw.pool.ntp.org, jp.pool.ntp.org, hk.pool.ntp.org, th.pool.ntp.org,time.windows.com, time.nist.gov, time.apple.com, time.asia.apple.com, dns1.synet.edu.cn, news.neu.edu.cn, dns.sjtu.edu.cn,dns2.synet.edu.cn, ntp.glnet.edu.cn, s2g.time.edu.cn, ntp-sz.chl.la, ntp.gwadar.cn, 3.asia.pool.ntp.org"
二、实例
由于比较简单就直接上源码了。
package com.android.vps.basic.protocol;
import android.os.SystemClock;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Arrays;
import java.util.Date;
public class NtpClient {
private static final String TAG = "NTPClient";
private static NtpClient mNtpClient = null;
private boolean mNtpClientState = false;
private boolean mGetNtpAsync = false;
private static final int ORIGINATE_TIME_OFFSET = 24;
private static final int RECEIVE_TIME_OFFSET = 32;
private static final int TRANSMIT_TIME_OFFSET = 40;
private static final int NTP_PACKET_SIZE = 48;
private static final int NTP_PORT = 123;
private static final int NTP_MODE_CLIENT = 3;
private static final int NTP_VERSION = 3;
// Number of seconds between Jan 1, 1900 and Jan 1, 1970
// 70 years plus 17 leap days
private static final long OFFSET_1900_TO_1970 = ((365L * 70L) + 17L) * 24L * 60L * 60L;
private NtpClient(){
mNtpClientState = false;
}
public synchronized static NtpClient getInstance(){
if(mNtpClient == null){
mNtpClient = new NtpClient();
}
return mNtpClient;
}
/**
* 开启ntp获取线程
*/
public void getNTPAsync(){
synchronized (this) {
if (mGetNtpAsync) {
Loger.d(TAG, "getNTPTime: mNtpClientState is false");
return ;
}
mGetNtpAsync = true;
new Thread(new Runnable(){
@Override
public void run() {
while(!requestNtp()){
try{
Thread.sleep(5*1000);
}catch (Exception e){
Loger.d(TAG, "run: " + e.toString());
}
}
}
}).start();
return;
}
}
/**
* 获取ntp获取状态
*/
public boolean getNtpState(){
return mNtpClientState;
}
private boolean requestNtp(){
boolean ret = false;
String[] urlList;
String NtpUrlList = "ntp1.aliyun.com, ntp2.aliyun.com, ntp3.aliyun.com, ntp4.aliyun.com, ntp5.aliyun.com, ntp6.aliyun.com, ntp7.aliyun.com," +
"cn.pool.ntp.org, cn.ntp.org.cn, sg.pool.ntp.org, tw.pool.ntp.org, jp.pool.ntp.org, hk.pool.ntp.org, th.pool.ntp.org," +
"time.windows.com, time.nist.gov, time.apple.com, time.asia.apple.com, dns1.synet.edu.cn, news.neu.edu.cn, dns.sjtu.edu.cn," +
"dns2.synet.edu.cn, ntp.glnet.edu.cn, s2g.time.edu.cn, ntp-sz.chl.la, ntp.gwadar.cn, 3.asia.pool.ntp.org";
///TODO:获取下发URL
try{
String url = ConfigManager.getInstance(SessionManager.getInstance().getAppContext()).getCfg(VPSConfigs.CONFIG_NTP_SERVER_URL);
if (url != null && url.length() != 0){
urlList = url.split(",",30);
for(String ntpUrl : urlList){
ret = requestNtp(ntpUrl, 30000);
if(ret){
Loger.d(TAG, "requestNTP: request ntp time ok : " + ntpUrl);
return ret;
}
try{
Thread.sleep(2*1000);
}catch (Exception e){
Loger.e(TAG, "run: " + e.toString());
}
}
}
}catch (Exception e){
Loger.e(TAG, "requestNTP error: " + e.toString());
}
try{
urlList = NtpUrlList.split(",",30);
for(String ntpUrl : urlList){
ret = requestNtp(ntpUrl, 30000);
if(ret){
Loger.d(TAG, "requestNTP: request ntp time ok : " + ntpUrl);
return ret;
}
try{
Thread.sleep(2*1000);
}catch (Exception e){
Loger.e(TAG, "run: " + e.toString());
}
}
}catch (Exception e){
Loger.e(TAG, "requestNTP error: " + e.toString());
}
return ret;
}
/**
* 请求ntp
* @param host
* @param timeout
* @return 是否获取成功
*/
private boolean requestNtp(String host, int timeout){
DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
long ntpTime = requestTime(host, timeout);
Loger.d(TAG, "requestNtp: mNtpTime " + dateFormat.format(ntpTime));
if (ntpTime == -1){
return false;
}
Date date = new Date();
//对比本地时间,差距1分钟则说明没准备好
try{
if((date.getTime()-ntpTime > 60*1000)||(date.getTime()-ntpTime < (-60*1000))){
return false;
}
}catch (Exception e){
Loger.e(TAG,"requestNtp error :" +e.toString());
}
mNtpClientState = true;
return true;
}
/**
* 请求ntp时间
* @param host
* @param timeout
* @return 成功返回获取时间 失败返回 -1
*/
private long requestTime(String host, int timeout) {
DatagramSocket socket = null;
InetAddress address = null;
long ntpTime = -1;
try {
address = InetAddress.getByName(host);
socket = new DatagramSocket();
socket.setSoTimeout(timeout);
byte[] buffer = new byte[NTP_PACKET_SIZE];
DatagramPacket request = new DatagramPacket(buffer, buffer.length, address, NTP_PORT);
buffer[0] = NTP_MODE_CLIENT | (NTP_VERSION << 3);
// get current time and write it to the request packet
final long requestTime = System.currentTimeMillis();
final long requestTicks = SystemClock.elapsedRealtime();
writeTimeStamp(buffer, TRANSMIT_TIME_OFFSET, requestTime);
socket.send(request);
// read the response
DatagramPacket response = new DatagramPacket(buffer, buffer.length);
socket.receive(response);
final long responseTicks = SystemClock.elapsedRealtime();
final long responseTime = requestTime + (responseTicks - requestTicks);
// extract the results
final byte leap = (byte) ((buffer[0] >> 6) & 0x3);
final byte mode = (byte) (buffer[0] & 0x7);
final int stratum = (int) (buffer[1] & 0xff);
final long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);
final long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);
final long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);
long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;
Loger.d(TAG, "Request time form ntp server success, " + address.toString() + " ,roundTripTime: " + roundTripTime);
ntpTime = responseTime + clockOffset;
} catch (Exception e) {
Loger.e(TAG, "Request time from ntp server failed ,msg: " + e.getMessage());
return ntpTime;
} finally {
if (socket != null) {
socket.close();
}
}
return ntpTime;
}
/**
* Reads an unsigned 32 bit big endian number from the given offset in the buffer.
*/
private long read32(byte[] buffer, int offset) {
byte b0 = buffer[offset];
byte b1 = buffer[offset + 1];
byte b2 = buffer[offset + 2];
byte b3 = buffer[offset + 3];
// convert signed bytes to unsigned values
int i0 = ((b0 & 0x80) == 0x80 ? (b0 & 0x7F) + 0x80 : b0);
int i1 = ((b1 & 0x80) == 0x80 ? (b1 & 0x7F) + 0x80 : b1);
int i2 = ((b2 & 0x80) == 0x80 ? (b2 & 0x7F) + 0x80 : b2);
int i3 = ((b3 & 0x80) == 0x80 ? (b3 & 0x7F) + 0x80 : b3);
return ((long) i0 << 24) + ((long) i1 << 16) + ((long) i2 << 8) + (long) i3;
}
/**
* Reads the NTP time stamp at the given offset in the buffer and returns
* it as a system time (milliseconds since January 1, 1970).
*/
private long readTimeStamp(byte[] buffer, int offset) {
long seconds = read32(buffer, offset);
long fraction = read32(buffer, offset + 4);
// Special case: zero means zero.
if (seconds == 0 && fraction == 0) {
return 0;
}
return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L);
}
/**
* Writes system time (milliseconds since January 1, 1970) as an NTP time stamp
* at the given offset in the buffer.
*/
private void writeTimeStamp(byte[] buffer, int offset, long time) {
// Special case: zero means zero.
if (time == 0) {
Arrays.fill(buffer, offset, offset + 8, (byte) 0x00);
return;
}
long seconds = time / 1000L;
long milliseconds = time - seconds * 1000L;
seconds += OFFSET_1900_TO_1970;
// write seconds in big endian format
buffer[offset++] = (byte) (seconds >> 24);
buffer[offset++] = (byte) (seconds >> 16);
buffer[offset++] = (byte) (seconds >> 8);
buffer[offset++] = (byte) (seconds >> 0);
long fraction = milliseconds * 0x100000000L / 1000L;
// write fraction in big endian format
buffer[offset++] = (byte) (fraction >> 24);
buffer[offset++] = (byte) (fraction >> 16);
buffer[offset++] = (byte) (fraction >> 8);
// low order bits should be random data
buffer[offset++] = (byte) (Math.random() * 255.0);
}
}
三、测试
有网络时,能正常获取到ntp时间。
无网络时,获取到的时间是1970年。
NTP地址好用的还是阿里的那几个。
四、时区设置
获取东八区时间
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
sdf.setTimeZone(TimeZone.getTimeZone("GMT+8"));
String snow = sdf.format(now);