android 时间同步

   在Android2.3.4系统中，Settings->Date & time->Automatic项打上后，时间会通过网络进行同步，而Android默认使用的是NITZ来获取移动网络时间，需要有移动网络服务商的支持才能使用，而有些Android产品只支持WIFI等无线网络，而不支持移动网络，此时就需要采用SNTP方式来获取网络时间进行同步了，相应需要修改到的文件为frameworks/base/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java和frameworks/base/telephony/java/com/android/internal/telephony/gsm/GsmServiceStateTracker.java这两个文件，需要修改的都是一样的内容，如下：
    添加如下内容：
    import android.net.SntpClient;
    修改如下内容：
    把
    private void revertToNitz() {
        if (Settings.System.getInt(phone.getContext().getContentResolver(),
                Settings.System.AUTO_TIME, 0) == 0) {
            return;
        }
        Log.d(LOG_TAG, "Reverting to NITZ: tz='" + mSavedTimeZone
                + "' mSavedTime=" + mSavedTime
                + " mSavedAtTime=" + mSavedAtTime);
        if (mSavedTimeZone != null && mSavedTime != 0 && mSavedAtTime != 0) {
            setAndBroadcastNetworkSetTimeZone(mSavedTimeZone);
            setAndBroadcastNetworkSetTime(mSavedTime
                    + (SystemClock.elapsedRealtime() - mSavedAtTime));
        }
    }
    修改为：
    private void revertToNitz() {
        if (Settings.System.getInt(phone.getContext().getContentResolver(),
                Settings.System.AUTO_TIME, 0) == 0) {
            return;
        }
        Log.d(LOG_TAG, "Reverting to NITZ: tz='" + mSavedTimeZone
                + "' mSavedTime=" + mSavedTime
                + " mSavedAtTime=" + mSavedAtTime);
        if (mSavedTimeZone != null && mSavedTime != 0 && mSavedAtTime != 0) {
            setAndBroadcastNetworkSetTimeZone(mSavedTimeZone);
            setAndBroadcastNetworkSetTime(mSavedTime
                    + (SystemClock.elapsedRealtime() - mSavedAtTime));
            return;
        }
        int tryCount = 5;
        SntpClient client = new SntpClient();

        Log.i(LOG_TAG, "revertToNitz new sntpclient");

        for(int i = 0; i < tryCount; i++){
            if(client.requestTime("north-america.pool.ntp.org", 10000)) {
                long cachedNtp = client.getNtpTime();
                long cachedNtpTimestamp = SystemClock.elapsedRealtime();

                Log.i(LOG_TAG, "Sntp NtpTime = " + cachedNtp);

                setAndBroadcastNetworkSetTime(cachedNtp
                   + (SystemClock.elapsedRealtime() - client.getNtpTimeReference()));
                return;
            }
        }
    }
    当不支持NITZ获取时间同步时就使用SNTP方式获取时间进行同步。不过使用SNTP方式进行时间同步时不能同步时区，需要自己先去掉自动同步并设置时区后再设置自动同步，这样才能进行网络时间的同步更新。

转载于:https://my.oschina.net/u/175434/blog/699994