前言
由于NTP服务在Android系统中已经存在，但是隐藏的系统API普通的开发手段无法调用。因此通过阅读相关源码就可以整理出我们自己可以使用的逻辑实现。
源码相关文件
-
frameworks/base/services/java/com/android/server/SystemServer.java
系统服务类，用于启动管理后续的系统服务，如NetworkTimeUpdateService -
frameworks/base/services/java/com/android/server/NetworkTimeUpdateService.java
通过onPollNetworkTime调用NtpTrustedTime.forceRefresh()获取NTP服务器时间 -
frameworks/base/core/java/android/util/NtpTrustedTime.java
创建SntpClient实例，调用SntpClient.requestTime()使用UDP协议请求网络时间 -
frameworks/base/core/java/android/net/SntpClient.java
发起服务器请求，并处理返回结果 -
frameworks/base/core/res/res/values/config.xml
Android系统配置ntpServer的文件路径
常用的可用的NTP服务器地址
基本官方通过这里查看https://www.pool.ntp.org/zh/zone/asia，但由于一些不可抗拒的原因有可能无法使用，目前整理出的可用的NTP服务器地址列表如下：
"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"
复制整理SntpClient.java文件
拿出系统的源码是不能直接使用的，有一些内部日志输出的方法我们也不需要使用，因此替换成android.util.Log的输出结果如下，可直接使用
/*
* Copyright (C) 2008 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.ziv.demo.ntptimeservice.services;
import android.net.Network;
import android.os.SystemClock;
import android.util.Log;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
/**
* Simple SNTP client class for retrieving network time.
*
* Sample usage:
* <pre>SntpClient client = new SntpClient();
* if (client.requestTime("time.foo.com")) {
* long now = client.getNtpTime() + SystemClock.elapsedRealtime() - client.getNtpTimeReference();
* }
* </pre>
*/
public class SntpClient {
private static final String TAG = "SntpClient";
private static final boolean DBG = true;
private static final int REFERENCE_TIME_OFFSET = 16;
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_MODE_SERVER = 4;
private static final int NTP_MODE_BROADCAST = 5;
private static final int NTP_VERSION = 3;
private static final int NTP_LEAP_NOSYNC = 3;
private static final int NTP_STRATUM_DEATH = 0;
private static final int NTP_STRATUM_MAX = 15;
// 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;
// system time computed from NTP server response
private long mNtpTime;
// value of SystemClock.elapsedRealtime() corresponding to mNtpTime
private long mNtpTimeReference;
// round trip time in milliseconds
private long mRoundTripTime;
private static class InvalidServerReplyException extends Exception {
public InvalidServerReplyException(String message) {
super(message);
}
}
/**
* Sends an SNTP request to the given host and processes the response.
*
* @param host host name of the server.
* @param timeout network timeout in milliseconds.
* @return true if the transaction was successful.
*/
public boolean requestTime(String host, int timeout) {
DatagramSocket socket = null;
InetAddress address = null;
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);
// set mode = 3 (client) and version = 3
// mode is in low 3 bits of first byte
// version is in bits 3-5 of first byte
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);
/* do sanity check according to RFC */
// TODO: validate originateTime == requestTime.
checkValidServerReply(leap, mode, stratum, transmitTime);
long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);
// receiveTime = originateTime + transit + skew
// responseTime = transmitTime + transit - skew
long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;
// = ((originateTime + transit + skew - originateTime) +
// (transmitTime - (transmitTime + transit - skew)))/2
// = ((transit + skew) + (transmitTime - transmitTime - transit + skew))/2
// = (transit + skew - transit + skew)/2
// = (2 * skew)/2 = skew
Log.d(TAG, "Request time form ntp server success, " + address.toString() + " ,roundTripTime: " + roundTripTime);
if (DBG) {
Log.d(TAG, "round trip: " + roundTripTime + "ms, " +
"clock offset: " + clockOffset + "ms");
}
// save our results - use the times on this side of the network latency
// (response rather than request time)
mNtpTime = responseTime + clockOffset;
mNtpTimeReference = responseTicks;
mRoundTripTime = roundTripTime;
} catch (Exception e) {
// if (DBG) {
// Log.e(TAG, "Error address: " + address.toString());
// }
Log.e(TAG, "Request time from ntp server failed ,msg: " + e.getMessage());
return false;
} finally {
if (socket != null) {
socket.close();
}
}
return true;
}
/**
* Returns the time computed from the NTP transaction.
*
* @return time value computed from NTP server response.
*/
public long getNtpTime() {
return mNtpTime;
}
/**
* Returns the reference clock value (value of SystemClock.elapsedRealtime())
* corresponding to the NTP time.
*
* @return reference clock corresponding to the NTP time.
*/
public long getNtpTimeReference() {
return mNtpTimeReference;
}
/**
* Returns the round trip time of the NTP transaction
*
* @return round trip time in milliseconds.
*/
public long getRoundTripTime() {
return mRoundTripTime;
}
private static void checkValidServerReply(
byte leap, byte mode, int stratum, long transmitTime)
throws InvalidServerReplyException {
if (leap == NTP_LEAP_NOSYNC) {
throw new InvalidServerReplyException("unsynchronized server");
}
if ((mode != NTP_MODE_SERVER) && (mode != NTP_MODE_BROADCAST)) {
throw new InvalidServerReplyException("untrusted mode: " + mode);
}
if ((stratum == NTP_STRATUM_DEATH) || (stratum > NTP_STRATUM_MAX)) {
throw new InvalidServerReplyException("untrusted stratum: " + stratum);
}
if (transmitTime == 0) {
throw new InvalidServerReplyException("zero transmitTime");
}
}
/**
* 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);
}
}
使用示例
注意，一定要在非主线程调用，并添加网络访问权限<uses-permission android:name="android.permission.INTERNET"/>
new Thread(){
@Override
public void run() {
SntpClient sntpClient = new SntpClient();
if (sntpClient.requestTime("cn.pool.ntp.org", 30000)) {
long now = sntpClient.getNtpTime() + SystemClock.elapsedRealtime() - sntpClient.getNtpTimeReference();
Date current = new Date(now);
Log.d(TAG, current.toString());
}
}
}.start();
结束语
Github地址：https://github.com/Ziv-Android/NTPTimeServiceDemo
RTFSC(Read the Fucking Source Code)
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