Convert java.util.Date to java.time's Instant, OffsetDateTime, or ZonedDateTime

As we migrate towards the modern java.time framework, it's essential to know how to convert legacy java.util.Date objects into the appropriate java.time types. Here's a rundown of the equivalencies:

java.util.Date to Instant

Both represent a moment in UTC, so the conversion is straightforward:

Instant instant = myUtilDate.toInstant();

java.util.Date myUtilDate = java.util.Date.from(instant);

java.util.Date to java.time's OffsetDateTime or ZonedDateTime

Since these types incorporate time zone information, extracting the zone from the legacy Date is necessary:

// If the legacy date is a GregorianCalendar (which can hold time zone info)
if (myUtilCalendar instanceof GregorianCalendar) {
    GregorianCalendar gregCal = (GregorianCalendar) myUtilCalendar;
    ZonedDateTime zdt = gregCal.toZonedDateTime(); // ZonedDateTime with time zone

    java.util.Calendar myUtilCalendar = java.util.GregorianCalendar.from(zdt);
}

Additional Conversion Mappings

Important Considerations

• Converting from a java.util.Date to a java.time type may result in loss of precision as nanosecond resolution is not supported by the legacy classes.
• When converting to OffsetDateTime or ZonedDateTime, the time zone information must be preserved to ensure correct interpretation.
• It's highly recommended to use java.time types in new code for enhanced precision and consistency.