My code does this to display the current date and time
DateTimeFormatter dtf = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM);
String formattedDate = dtf.format(LocalDateTime.now());
Because I use GMT anyway I didnt notice it always displaying using GMT timezone was reported by customer in different timezone. But I am confused because I thought LocalDateTime was the local datetime ?
LocalDateTime not have Zone, instead use ZonedDateTime:
String formattedDate = dtf.format(ZonedDateTime.now());
Beside, your DateTimeFormatter can't display the zone, to do this, you have to use FormatStyle.LONG instead of FormatStyle.MEDIUM
From the javadoc:
A date-time without a time-zone
If you want to have a LocalDateTime with a zone you can use atZone():
ZonedDateTime zdt = someLocalDateTime.atZone(ZoneId.systemDefault());
String formattedDate = zdt.format(dtf);
The customer is running your program on a system that has UTC configured as the default time zone.
You could tell the customer to change the time zone on the computer, or at least for your program specifically, but they probably won't do that. There are good reasons to run computers with the clock set to UTC.
Another solution might be to add the user's preferred time zone to your program settings, and use it consistently. For example:
String userPreferredTz = "Asia/Tokyo"; // Read from user preferences or settings file
ZoneId userZoneId = ZoneId.of(userPreferredTz);
dtf.format(ZonedDateTime.now(userZoneId))
I thought LocalDateTime was the local datetime
This is correct. LocalDateTime is the local date-time i.e. using the system's default time-zone unless you specify a time-zone with it e.g. if you run the following statement on a machine set with Europe/London timezone, it will show the date-time in GMT and if you run it on a machine set with Asia/Kolkata timezone, it will show the date-time in IST (India Standard Time):
System.out.println(LocalDateTime.now());
However, if you run the following statement on any machine, it will always give you the date-time of IST:
System.out.println(LocalDateTime.now(ZoneId.of("Asia/Kolkata")));
Since the LocalDateTime and LocalDate do not have a zone or offset information, you would like to use ZonedDateTime or OffsetDateTime as per your requirement. The following table (Ref) gives you an overview of all the date-time classes and you can choose one from it as per your requirement:
