andorid 如何获得网络时间

我们知道在android手机的设置时间中有个"自动日期和时间"的选项，来获得网络时间，如何获得网络时间哪，在android源码中有一个SntpClient类，通过此类可以获得网络时间，

可以将此类移植到你的项目中去，主要代码如下：

                                SntpClient client = new SntpClient();if (client.requestTime("2.android.pool.ntp.org", 10000)) {Long time = client.getNtpTime()+ SystemClock.elapsedRealtime()- client.getNtpTimeReference();Date date = new Date(time);SimpleDateFormat fromat = new SimpleDateFormat("yyyy--MM--dd HH:mm:ss");view.setText(fromat.format(date));}

SntpClient 类源码：

package com.android.activitys;/* * 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. */import java.net.DatagramPacket;import java.net.DatagramSocket;import java.net.InetAddress;import android.os.SystemClock;import android.util.Log;/** * {@hide} * * 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 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_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;    // 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;    /**     * 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;        try {            socket = new DatagramSocket();            socket.setSoTimeout(timeout);            InetAddress address = InetAddress.getByName(host);            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            long requestTime = System.currentTimeMillis();            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);            long responseTicks = SystemClock.elapsedRealtime();            long responseTime = requestTime + (responseTicks - requestTicks);            // extract the results            long originateTime = readTimeStamp(buffer, ORIGINATE_TIME_OFFSET);            long receiveTime = readTimeStamp(buffer, RECEIVE_TIME_OFFSET);            long transmitTime = readTimeStamp(buffer, TRANSMIT_TIME_OFFSET);            long roundTripTime = responseTicks - requestTicks - (transmitTime - receiveTime);            // receiveTime = originateTime + transit + skew            // responseTime = transmitTime + transit - skew            // 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            long clockOffset = ((receiveTime - originateTime) + (transmitTime - responseTime))/2;            // if (false) Log.d(TAG, "round trip: " + roundTripTime + " ms");            // if (false) Log.d(TAG, "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 (false) Log.d(TAG, "request time failed: " + e);            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;    }    /**     * 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);        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) {        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);    }}