Android版本，回到夏令时会错吗？

Question

This date was sent from my app looking like this:

2014-10-29 09:00:17

The database stores it like this:

Wed Oct 29 2014 09:00:17 GMT+0100 (CET)

I'm getting a date back from my server looking like the this:

2014-10-29T08:00:17.000Z (one our less)

Then I'm converting it to a calendar date like this:

public static long getUTCToMillis(String time) {
    Calendar cal = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.getDefault());
    sdf.setTimeZone(TimeZone.getTimeZone("CET")); 
    try {
        cal.setTime(sdf.parse(time));
        return cal.getTimeInMillis();
    } catch (ParseException e) {
        e.printStackTrace();
    }
    return -1;
}

This always sets the hour to 08:00 but I want it to be converted back to 09:00 like it was saved. If I put timezone to UTC I get 09:00 but how will that work when summer time starts again? How can I get this to display the correct time?

Answer 1

Take a look at TimeZone.getOffset(long time)

The method returns the time difference between UTC and your target timezone.

So you can do something like this:

public static long getUTCToMillis(String time) {
    Calendar cal = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.getDefault());

    TimeZone timezone = TimeZone.getTimeZone("CET");

    try {
        Date date = sdf.parse(time);
        long offSet = timezone.getOffset(date.getTime());
        cal.setTime(date);
        cal.add(Calendar.MILLISECOND, offset);
        return cal.getTimeInMillis();
    } catch (ParseException e) {
        e.printStackTrace();
    }
    return -1;
}

As a side note, I suggest you store time values in UTC regardless of where your user is. For example, if your application is used in two different time zones simultaneously, the server should store the same value. Time conversion will and should be done locally on user's device based on the time zone he/she is in.