How to parse format dates with LocalDateTime Java 8

Question

I have date and time as string (e.g. "2014-04-08 12:30"). How can I obtain a LocalDateTime instance from the given string?

After I finished working with the LocalDateTime object: How can I then convert the LocalDateTime instance back to a string with the same format as shown above?

Answer 1

To create a LocalDateTime object from a string you can use the static LocalDateTime.parse() method. It takes a string and a DateTimeFormatter as parameter. The DateTimeFormatter is used to specify the date/time pattern.

String str = "1986-04-08 12:30";
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
LocalDateTime dateTime = LocalDateTime.parse(str, formatter);

Formatting date and time

To create a formatted string out a LocalDateTime object you can use the format() method.

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
LocalDateTime dateTime = LocalDateTime.of(1986, Month.APRIL, 8, 12, 30);
String formattedDateTime = dateTime.format(formatter); // "1986-04-08 12:30"

Note that there are some commonly used date/time formats predefined as constants in DateTimeFormatter. For example: Using DateTimeFormatter.ISO_DATE_TIME to format the LocalDateTime instance from above would result in the string "1986-04-08T12:30:00".

The parse() and format() methods are available for all date/time related objects (e.g. LocalDate or ZonedDateTime)

Answer 2

Converting LocalDateTime to Time Zone ISO8601 String

LocalDateTime d1 = LocalDateTime.now(); 
ZonedDateTime d2 = d1.atZone(ZoneOffset.UTC); //you might use a different zone
String iso8601 = d2.toString();

Converting from ISO8601 String back to a LocalDateTime

String iso8601 = "2016-02-14T18:32:04.150Z";
ZonedDateTime d3 = ZonedDateTime.parse(iso8601);
LocalDateTime d4 = d3.toLocalDateTime();