Time zones - how to?

Question

The final goal is to convert a timestamp passed down from the server to local time.

Here's what I get:

2018-04-05T16:14:19.130Z

However, my local time is 11:14 AM CST. Here's what I've tried:

 final DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
 final LocalTime localTime = formatter.parseLocalTime(text);
 Timber.i(localTime.toString()); // output: 16:14:19.070

Output is: 16:14:19.070. Does anybody know how to use it? I expected to receive something like 11:14 AM.

Also, I've tried using this:

 final DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
 final DateTime time = formatter.parseDateTime(text);
 Timber.i(time.toString());  // output: 2018-04-05T16:14:19.490-05:00

Looks like it's a 5-hour difference there? Does anybody know how I can use this to convert to local time?

Answer 1

The "Z" in the end means that the date/time is in UTC. If you put it inside quotes, it's treated as a literal (the letter "Z" itself) and it loses this special meaning - you're basically throwing away the information that it's in UTC, and DateTime assumes the JVM default timezone (that's why your second attempt results in 16:14 in UTC-05:00).

DateTime can parse this input directly:

String input = "2018-04-05T16:14:19.130Z";
DateTime dt = DateTime.parse(input);

Then you convert this to the desired timezone. You can do:

dt = dt.withZone(DateTimeZone.getDefault());

Which will use your JVM's default timezone. But this is not so reliable, because the default can be changed at runtime - even by other applications running in the same JVM - so it's better to use an explicit timezone:

dt = dt.withZone(DateTimeZone.forID("America/Chicago"));

Then you can convert it to the format you want:

String time = dt.toString("hh:mm a"); // 11:14 AM

---

If you need to use a formatter, you can remove the quotes around "Z" and also set the timezone in the formatter:

DateTimeFormatter parser = DateTimeFormat.forPattern("yyyy-MM-dd'T'HH:mm:ss.SSSZ")
    // zone to be used for the formatter
    .withZone(DateTimeZone.forID("America/Chicago"));
DateTime dateTime = parser.parseDateTime("2018-04-05T16:14:19.130Z");
String time = dateTime.toString("hh:mm a"); // 11:14 AM

Answer 2

Use this method to convert your time to local:

 public static String convertTimeToLocal(String dateStr) {

        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = null;

        try {
            date = format.parse(dateStr);
            System.out.println(date);
        } catch (ParseException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        String timeZone = Calendar.getInstance().getTimeZone().getID();
        Date local = new Date(date.getTime() + TimeZone.getTimeZone(timeZone).getOffset(date.getTime()));
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.ENGLISH);
        String reportDate = df.format(local);

        return reportDate;
    }

& for AM and PM, use this method:

public static String convertTimeToAmPm(String time) {
        List<String> arr = Arrays.asList(time.split(":"));
        int hours = Integer.parseInt(arr.get(0));
        int mins = Integer.parseInt(arr.get(1));

        String timeSet = "";
        if (hours > 12) {
            hours -= 12;
            timeSet = "PM";
        } else if (hours == 0) {
            hours += 12;
            timeSet = "AM";
        } else if (hours == 12)
            timeSet = "PM";
        else
            timeSet = "AM";

        String minutes = "";
        if (mins < 10)
            minutes = "0" + mins;
        else
            minutes = String.valueOf(mins);
        // Append in a StringBuilder
        String aTime = new StringBuilder().append(hours).append(':')
                .append(minutes).append(" ").append(timeSet).toString();
        return aTime;
    }