如何从日历中获取 UTC 时间戳？

在Java中，当我使用时，我得到当前时区的对象。但通常以 UTC 时间存储，而不是以本地时间存储。那么如何从日历实例获取 UTC 时间呢？Calendar.getInstance();Calendarjava.sql.Timestamp

    DateFormat df = DateFormat.getTimeInstance();
    Calendar cal = Calendar.getInstance();
    Timestamp time = new Timestamp(cal.getTimeInMillis());

    // Prints local time
    System.out.println(df.format(new Date(time.getTime())));

    // Printe local time, but I want UTT Time
    System.out.println("timestamp: " + time);