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In my sqlite database I have a table with a field created_at that stores time in ISO8601 as text. In the object corresponding to this table I have two fields String date, String time for the created_at attribute. Now, while querying for this table and creating a corresponding object I am stuck at converting the ISO8601 string to the current user's timezone's date (YYYY/MM/DD), time (XX:YY pm). Could anyone help me out? I thought of using substring to split the string but then the timezone is UTC for ISO8601 strings.

The ISO8601 string is stored in the database using Instant.now().toString()

tldr: created_at = ISO8601 time string; need to extract date and time portion from it for the current user.

learner
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  • @user16320675 Instant.now().toString(); – learner Apr 07 '22 at 20:57
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    like `"2022-04-07T21:07:26.961524500Z"`? so just `Instant.parse(text)` and then `ZonedDateTime.ofInstant()` with the desired `ZoneId` (e.g. `TimeZone.getDefault().toZoneId()`) – user16320675 Apr 07 '22 at 21:10
  • [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) comes in many variants. Please paste an example or two of what you have got. – Ole V.V. Apr 08 '22 at 05:27
  • @learner *why is it being downvoted?* I didn’t downvote either. My guess is it’s for lack of demonstration of a search and research effort on your part. It’s better to tell us what your search brought up and specify in what way it was insufficient for reaching your goal. – Ole V.V. Apr 10 '22 at 10:39

2 Answers2

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Read the Wikipedia page on ISO 8601.

java.time

Capture the current moment as seen in UTC.

Instant instant = Instant.now() ;

Generate ISO 8601 string.

String output = instant.toString() ;

The Z on the end of that resulting string means an offset-from-UTC of zero hours-minutes-seconds.

Adjust into a particular time zone.

ZoneId z = ZoneId.of( "Asia/Tokyo" ) ;
ZonedDateTime zdt = instant.atZone( z ) ;

Unfortunately, the ISO 8601 standard does not define a format for a moment as seen in a time zone. The ZonedDateTime#toString method uses a format similar to ISO 8601 but appends the name of the time zone in square brackets. This is a smart solution.

String output = zdt.toString() ;

Much of your Question in not clear. I am guessing you want to pull the date and time portions from a ZonedDateTime. But I am not sure using such values to query your database makes sense. But if you insist:

LocalDate ld = zdt.toLocalDate() ;
LocalTime lt = zdt.toLocalTime() ;

You can get an ISO 8601 string for each.

String ldOutput = ld.toString() ;
String ltOutput = lt.toString() ;

Notice there is no need for the string manipulations you mentioned in your Question.

Basil Bourque
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I think that you can see this link here you might find some answers.

But for example, you can see this example here. I have a String format and I transform it into a Date object.

DateFormat df1 = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSSZ");
String string1 = "2001-07-04T12:08:56.235-0700";
Date result1 = df1.parse(string1);
pedro
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