ZonedDateTime toString compatability with ISO 8601

Question

I am trying to ensure that calling toString() on my ZonedDateTime Object will comply with ISO-8601 format.

The documentation for the toSt

Answer 1

I like above JodaStephen's last comment 'or a formatter', since using formatter is more robust regardless of data. The reason is OffsetDateTime toString() skip second unit part when there is no value on second unit and below, so it ends up gives yyyy-MM-ddTHH:mmZ instead of yyyy-MM-ddTHH:mm:ssZ. That can cause trouble if other system expects static format and has no adaptability.

Below is the code I used for simulating both cases where has no time portion and has it.

/**
 * This function is design to convert Date object from other system to ISO dateTime String 
 * which will be sent to another system. and using formatter to lock up the format
 * @param date java.util.Date
 * @return 'yyyy-MM-ddTHH:mm:ssZ' format ISO dateTime string
 */
public String formatIsoUtcDateTime(Date date) {
    if(null == date) {
        return null;
    }
    return ZonedDateTime.ofInstant(date.toInstant(), ZoneId.of("UTC"))
                        .format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss'Z'"));
}

// no time portion with using formatter
SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
Date date = sdf.parse("20171010");
System.out.println(formatIsoUtcDateTime(date));

// no time portion with using OffsetDateTime toString
System.out.println(ZonedDateTime.ofInstant(date.toInstant(), ZoneId.of("UTC")).toOffsetDateTime().toString());

// just current date and probably has at least millisecond, using formatter
System.out.println(formatIsoUtcDateTime(new Date()));

// just current date and probably has at least millisecond, using OffsetDateTime toString
// this will print yyyy-MM-ddTHH:mm:ss.SSSZ format
System.out.println(ZonedDateTime.ofInstant(new Date().toInstant(), ZoneId.of("UTC")).toOffsetDateTime().toString());