Date Type Conversion

DateTypeConvert converts legacy Date, Calendar, SQL date types, epoch milliseconds, and Java 8 java.time values. Supply a ZoneId whenever a conversion needs a civil time zone.

Instant instant = Instant.now();
ZoneId zone = ZoneId.of("Asia/Shanghai");

LocalDateTime local = new DateTypeConvert(instant).to(LocalDateTime.class, zone);
Calendar calendar = new DateTypeConvert(instant).to(Calendar.class, zone);

Important semantics

• Epoch value 0 is valid and represents 1970-01-01T00:00:00Z.
• Date-only strings are parsed as dates instead of being forced through a date-time formatter.
• Parsing and output formatting use separate formatters. Parsing is strict, so invalid values such as 2023-02-29 raise a parsing exception instead of being silently adjusted.
• Converting LocalDate to LocalDate returns the original value without applying zone rules, so a skipped civil date in the supplied zone cannot change the date.
• A Calendar result uses the requested zone, not an unrelated system-default calendar.
• A Calendar input retains its own time zone when no ZoneId is supplied; an explicitly supplied ZoneId takes precedence.
• ZonedDateTime and OffsetDateTime inputs are returned unchanged when the requested target is the same type, preserving their original zone or offset.
• Converting LocalDateTime to an instant is strict: a daylight-saving gap is rejected, and an overlap is rejected as ambiguous instead of silently choosing an offset.
• OffsetTime has no date. It may be converted only to OffsetTime or LocalTime; instant-based conversions are rejected rather than attaching the system's current date.
• LocalTime is returned unchanged when requested as LocalTime. It can become an OffsetTime only with an explicit fixed offset; other date-dependent conversions are rejected.

Instant epoch = new DateTypeConvert(0L).to(Instant.class, ZoneOffset.UTC);
assertEquals(Instant.EPOCH, epoch);

If no input has been set or a conversion is inherently ambiguous, the API throws an exception instead of silently inventing missing context.