How to convert a TemporalAccessor a milliseconds timestamp (using Instant)

I am trying to convert a TemporalAccessor to milliseconds unix timestamp but I am getting an error in some cases.

Here is a code sample to reproduce the problem :

    DateTimeFormatter formatter = new DateTimeFormatterBuilder()
        .appendPattern("yyyy-MM-dd HH:mm:ss")
        .appendFraction(ChronoField.MICRO_OF_SECOND, 0, 6, true)
        .toFormatter();
    TemporalAccessor accessor = formatter.parse("1970-01-01 00:01:00.00");
    Instant instant = Instant.from(accessor);
    Instant.EPOCH.until(instant, ChronoUnit.MILLIS);

Here is the error I am getting :

Exception in thread "main" java.time.DateTimeException: Unable to obtain Instant from TemporalAccessor: {},ISO resolved to 1970-01-01T00:01 of type java.time.format.Parsed

I am getting this error only with this date format so the problem may come from my DateTimeFormatter (originally i was using an other one way more generic and I am only getting the error for this format).

You need to specify the timezone in your DateTimeFormatter as follows:

DateTimeFormatter formatter = new DateTimeFormatterBuilder()
        .appendPattern("yyyy-MM-dd HH:mm:ss")
        .appendFraction(ChronoField.MICRO_OF_SECOND, 0, 6, true)
        .toFormatter()
        .withZone(ZoneId.systemDefault());
TemporalAccessor accessor = formatter.parse("1970-01-01 00:01:00.00");
Instant instant = Instant.from(accessor);
Instant.EPOCH.until(instant, ChronoUnit.MILLIS);