86. Converting Calendar to LocalDateTime

In Problem 68, you saw that converting a java.util.Date (date) to a LocalTime can be done as follows:

LocalTime lt = date.toInstant().atZone(zoneId).toLocalTime();

In the same manner, we can convert a java.util.Date to a LocalDateTime (here, zoneId was replaced with ZoneId.systemDefault()):

LocalDateTime ldt = date.toInstant().atZone(
  ZoneId.systemDefault()).toLocalDateTime();

We also know that we can obtain a java.util.Date from a Calendar via the getTime() method. So, by gluing the pieces of the puzzle together, we obtain the following code:

public static LocalDateTime
       toLocalDateTime(Calendar calendar) {
  Date date = calendar.getTime();
  return date.toInstant().atZone(
    ZoneId.systemDefault()).toLocalDateTime();
}

The same result but following a shorter path can be obtained like this:

return LocalDateTime.ofInstant(Instant.ofEpochMilli(
  calendar.getTimeInMillis()), ZoneId.systemDefault());

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