1.8 기준 공식 문서 참고 appendFraction(ChronoField.NANO_OF_SECOND, 0, 9, true) field - the field to append, not null minWidth - the minimum width of the field excluding the decimal point, from 0 to 9 maxWidth - the maximum width of the field excluding the decimal point, from 1 to 9 decimalPoint - whether to output the localized decimal point symbol Thread 환경(toFormatter() 써야 안전한듯..) This class is a muta..