Get Day, Month, Year from Java Calendar instance

Question

I have an Instant derived from a Java Calendar , eg c.toInstant() , and now in a different location convert that to a custom Date object that needs a day of the month, month, and year. I tried:

    if (instance.isSupported(ChronoField.DAY_OF_MONTH) && instance.isSupported(ChronoField.MONTH_OF_YEAR) && instance.isSupported(ChronoField.YEAR)) {
      return new com.company.common.Date()
          .setDay(instance.get(ChronoField.DAY_OF_MONTH))
          .setMonth(instance.get(ChronoField.MONTH_OF_YEAR))
          .setYear(instance.get(ChronoField.YEAR));
    }

But when I try to compile ErrorProne throws:

...impl/utils/DateUtils.java:21: error: [TemporalAccessorGetChronoField] TemporalAccessor.get() only works for certain values of ChronoField.
          .setDay(instance.get(ChronoField.DAY_OF_MONTH))
                              ^

I'm not sure why I can't find an answer for this anywhere, but after some searching I came up with nothing helpful -- though I probably missed something.

Answer 1

Instant is only a timestamp - it only provides seconds, millis and nanos.

If you start with a calendar instance in the first place you should be able to simply use

calendar.get(Calendar.YEAR)
calendar.get(Calendar.MONTH)
calendar.get(Calendar.DAY_OF_YEAR)

directly to fetch the date values and skip the conversion to Instant.

If you prefer working with the newer time API you can fetch dates and time from a ZonedDateTime like

    Calendar calendar = Calendar.getInstance();
    ZonedDateTime zonedDateTime = ZonedDateTime.ofInstant(calendar.toInstant(), calendar.getTimeZone().toZoneId());

    zonedDateTime.getYear();
    zonedDateTime.getMonthValue();
    zonedDateTime.getDayOfMonth();

I don't see a direct advantage for the example given, but it could be useful if you want to use further functionality of the newer java.util.time API