How to get in this date format?

Question

I am getting two date fields from JSON as text like this May 22 12:05:41 UTC 2018 and 2018-05-22 12:05:41.512 but I have to change to MM-dd-yyyy HH:mm:ss format.

Answer 1

Just to be clear - date/time objects are format agnostic. They are simply containers for the amount of time which has passed since a fixed point in time (usually the Unix Epoch), so you can't change their format per se.

However, you can, generate a String of a prescribed pattern.

When dealing with date/time in Java you should make use of the date/time APIs introduced in Java 8 (or the ThreeTen back port)

For example...

String date1 = "May 22 12:05:41 UTC 2018";
DateTimeFormatter format1 = DateTimeFormatter.ofPattern("MMM dd HH:mm:ss z yyyy", Locale.ENGLISH);
LocalDateTime ldt1 = LocalDateTime.parse(date1, format1);

String date2 = "2018-05-22 12:05:41.512";
DateTimeFormatter format2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSS", Locale.ENGLISH);
LocalDateTime ldt2 = LocalDateTime.parse(date2, format2);

DateTimeFormatter format3 = DateTimeFormatter.ofPattern("MM-dd-yyyy HH:mm:ss", Locale.ENGLISH);
System.out.println(ldt1.format(format3));
System.out.println(ldt2.format(format3));

Which outputs...

05-22-2018 12:05:41
05-22-2018 12:05:41

Since one of your inputs has a timezone associated with it, it would be appropriate to take it into consideration

ZonedDateTime zdt = ZonedDateTime.parse(date1, format1);
LocalDateTime ldt1 = zdt.withZoneSameInstant(ZoneId.systemDefault()).toLocalDateTime();

which outputs (for my current location)

05-22-2018 22:05:41

Answer 2

You can use this code

DateFormat format = new SimpleDateFormat("MM-dd-yyyy HH:mm:ss");
DateFormat inputFormat1 = new SimpleDateFormat("MMM dd HH:mm:ss z yyyy");
DateFormat inputFormat2 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
String date1 = "May 22 12:05:41 UTC 2018";
String date2 = "2018-05-22 12:05:41.512";
System.out.println(format.format(inputFormat1.parse(date1)));
System.out.println(format.format(inputFormat2.parse(date2)));