public class Test {

  private static final DateTimeFormatter FORMAT = new DateTimeFormatterBuilder()
    .appendValue(ChronoField.YEAR, 1, 9, SignStyle.NORMAL)
    .appendLiteral('-')
    .appendValue(ChronoField.MONTH_OF_YEAR, 1, 2, SignStyle.NEVER)
    .appendLiteral('-')
    .appendValue(ChronoField.DAY_OF_MONTH, 1, 2, SignStyle.NEVER)
    .optionalStart() // time component
    .appendLiteral(' ')
    .appendValue(ChronoField.HOUR_OF_DAY, 1, 2, SignStyle.NEVER)
    .appendLiteral(':')
    .appendValue(ChronoField.MINUTE_OF_HOUR, 1, 2, SignStyle.NEVER)
    .appendLiteral(':')
    .appendValue(ChronoField.SECOND_OF_MINUTE, 1, 2, SignStyle.NEVER)
    .optionalStart() // nanos
    .appendLiteral('.')
    .appendFraction(ChronoField.NANO_OF_SECOND, 1, 9, false)
    .optionalEnd() // nanos
    .optionalEnd() // time componont
    .optionalStart() // zone or offset
    .appendLiteral(' ')
    .appendZoneOrOffsetId() //TODO doesn't work as it should due to bug in JRE
    .optionalEnd() // zone or offset
    .toFormatter();

  public static void main(String[] args) throws Exception {
    for (String s : new String[] {"1970-01-01 00:00:00 +00:00", "1999-12-31 23:59:59 -08:00"}) {
      try {
        System.out.println("\t"+OffsetDateTime.parse(s, FORMAT));
      }
      catch (Exception e) {
        System.err.println("\t"+e);
      }
    }
  }

}