java - Android Studio Convert ISO string to "America/New_York" when adding to event to calendar

Question

I am trying to convert a string "2018-10-17T22:00:00Z" to eastern time zone when adding it as an event to a calendar, but instead of it adding the event time as 6pm it is adding it as 10pm. Any help would be appreciated.

String[] segments = uri.getPath().split("/");
Date startDate = null;
Date endDate = null;
Activity activity = (Activity) context;
String stTime = "2018-10-17T22:00:00Z";
String enTime = "2018-10-17T23:00:00Z";
String eventTitle = segments[3];
String eventLocation = segments[4];

TimeZone timezone = TimeZone.getTimeZone("America/New_York");

SimpleDateFormat formatStart = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
formatStart.setTimeZone(timezone);

SimpleDateFormat formatEnd = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
formatEnd.setTimeZone(timezone);

try {
    startDate = formatStart.parse(stTime);
    endDate = formatEnd.parse(enTime);
} catch (ParseException e) {
    e.printStackTrace();
}

Calendar calStart = new GregorianCalendar(timezone);
calStart.setTime(startDate);

Calendar calEnd = new GregorianCalendar(timezone);
calEnd.setTime(endDate);


if (ActivityCompat.checkSelfPermission(this.context, android.Manifest.permission.WRITE_CALENDAR) != PackageManager.PERMISSION_GRANTED) {
    ActivityCompat.requestPermissions(activity, new String[]{android.Manifest.permission.WRITE_CALENDAR},1);
}

Calendar beginTime = Calendar.getInstance();
beginTime.set(calStart.get(Calendar.YEAR), calStart.get(Calendar.MONTH), calStart.get(Calendar.DAY_OF_MONTH), calStart.get(Calendar.HOUR_OF_DAY), calStart.get(Calendar.MINUTE));

Calendar endTime = Calendar.getInstance();
endTime.set(calEnd.get(Calendar.YEAR), calEnd.get(Calendar.MONTH), calEnd.get(Calendar.DAY_OF_MONTH), calEnd.get(Calendar.HOUR_OF_DAY), calEnd.get(Calendar.MINUTE));

ContentResolver cr = context.getContentResolver();
ContentValues values = new ContentValues();
values.put(CalendarContract.Events.DTSTART, beginTime.getTimeInMillis());
values.put(CalendarContract.Events.DTEND, endTime.getTimeInMillis());
values.put(CalendarContract.Events.TITLE, eventTitle);
values.put(CalendarContract.Events.CALENDAR_ID, 1);
values.put(CalendarContract.Events.EVENT_TIMEZONE, "America/New_York");
values.put(CalendarContract.Events.EVENT_LOCATION, eventLocation);

cr.insert(CalendarContract.Events.CONTENT_URI, values);
Toast.makeText(context, "Successfully Added Event", Toast.LENGTH_SHORT).show();

Answer 1

That is because you're telling the parser to ignore the Z, or rather to match it literally, but not to process it's meaning.

The input strings are Instant values, so parse to Instant, then apply time zone.
If you don't have Java 8+ compatible Android, use ThreeTenABP.

String stTime = "2018-10-17T22:00:00Z";

ZonedDateTime time = Instant.parse(stTime).atZone(ZoneId.of("America/New_York"));
System.out.println(time); // prints: 2018-10-17T18:00-04:00[America/New_York]

If you prefer using antiquated SimpleDateFormat, simply use the correct format, and don't specify time zone.

SimpleDateFormat formatStart = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssX");
Date startDate = formatStart.parse(stTime);
// My default time zone is America/New_York, so:
System.out.println(startDate); // prints: Wed Oct 17 18:00:00 EDT 2018

startDate.getTime() is the time-in-millis you need.

For API Level < 24, format pattern X doesn't work, so you need to do the hardcoded Z like in your question, but tell the parser that it is in UTC, because that is what the Z time zone means.

SimpleDateFormat formatStart = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");
formatStart.setTimeZone(TimeZone.getTimeZone("UTC"));
Date startDate = formatStart.parse(stTime);
// My default time zone is America/New_York, so:
System.out.println(startDate); // prints: Wed Oct 17 18:00:00 EDT 2018