android 時間同步

 

   在Android2.3.4系統中，Settings->Date & time->Automatic項打上後，時間會通過網絡進行同步，而Android默認使用的是NITZ來獲取移動網絡時間，需要有移動網絡服務商的支持才能使用，而有些Android產品只支持WIFI等無線網絡，而不支持移動網絡，此時就需要採用SNTP方式來獲取網絡時間進行同步了，相應需要修改到的文件爲frameworks/base/telephony/java/com/android/internal/telephony/cdma/CdmaServiceStateTracker.java和frameworks/base/telephony/java/com/android/internal/telephony/gsm/GsmServiceStateTracker.java這兩個文件，需要修改的都是一樣的內容，如下：
    添加如下內容：
    import android.net.SntpClient;
    修改如下內容：
    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));
        }
    }
    修改爲：
    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;
            }
        }
    }
    當不支持NITZ獲取時間同步時就使用SNTP方式獲取時間進行同步。不過使用SNTP方式進行時間同步時不能同步時區，需要自己先去掉自動同步並設置時區後再設置自動同步，這樣才能進行網絡時間的同步更新。