再現可能なシナリオを示すために、次のことを行っています
現在のシステム時刻 (現地時間) を取得する
現地時間を UTC に変換 // ここまでは正常に動作
UTC 時間を逆にして、現地時間に戻します。3 つの異なるアプローチ (以下にリスト) に従いましたが、3 つのアプローチはすべて UTC でのみ時刻を保持します。
{
long ts = System.currentTimeMillis(); Date localTime = new Date(ts); String format = "yyyy/MM/dd HH:mm:ss"; SimpleDateFormat sdf = new SimpleDateFormat (format); // Convert Local Time to UTC (Works Fine) sdf.setTimeZone(TimeZone.getTimeZone("UTC")); Date gmtTime = new Date(sdf.format(localTime)); System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime()); // Reverse Convert UTC Time to Locale time (Doesn't work) Approach 1 sdf.setTimeZone(TimeZone.getDefault()); localTime = new Date(sdf.format(gmtTime)); System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime()); // Reverse Convert UTC Time to Locale time (Doesn't work) Approach 2 using DateFormat DateFormat df = new SimpleDateFormat (format); df.setTimeZone(TimeZone.getDefault()); localTime = df.parse((df.format(gmtTime))); System.out.println("Local:" + localTime.toString() + "," + localTime.getTime() + " --> UTC time:" + gmtTime.toString() + "-" + gmtTime.getTime()); // Approach 3 Calendar c = new GregorianCalendar(TimeZone.getDefault()); c.setTimeInMillis(gmtTime.getTime()); System.out.println("Local Time " + c.toString());
}