ZonedDateTime convert to string.
ZonedDateTime convert to string.
customized format: default "yyyy/MM/dd HH:mm:ss"
ZonedDateTime convert to string with default date formatter.
ZonedDateTime to this day, 23:59:59
ZonedDateTime to this hour, HH:59:59
ZonedDateTime to this day, 00:00:00
ZonedDateTime to this hour, HH:00:00
ZonedDateTime to unixtime