Package dev.frostlake.task

Class CronSchedule

java.lang.Object
dev.frostlake.task.CronSchedule
public final class CronSchedule extends Object
A task's USING CRON <minute> <hour> <day-of-month> <month> <day-of-week> <time zone> schedule, parsed once and asked for its next fire time on the calendar.

The grammar is the subset a real account accepts, field by field (live-verified): numbers, *, lists, ranges, and steps — */n, a-b/n, and a/n, which runs from a to the field's maximum; month names JAN–DEC and day names SUN–SAT in any case; L in the day-of-month field (the month's last day, also as a list item); and nL or FRIL in the day-of-week field (the month's last such weekday). Day of week is 0–6. Refused, all with the one invalid-schedule sentence: ?, #, W, a bare day-of-week L, L-3, a day-of-week 7, a step of 0, a reversed range, an empty list item, an out-of-range value, and any field count but five.

★ DAY OF MONTH AND DAY OF WEEK ARE OR-ED WHEN BOTH ARE RESTRICTED: 0 0 1 * MON fires on the 1st AND on every Monday, and a stepped */2 counts as restricted there. When either field is a bare *, the other alone decides.

★ THE LAST TOKEN IS ALWAYS THE ZONE, which is why five fields and no zone are refused as an unrecognized zone named "*". It must be a region name the TIMEZONE parameter accepts — UTC, Etc/GMT+5, America/Los_Angeles, in any case — while an offset such as +01:00 or an abbreviation such as PST is refused with a sentence naming it.

  • Field Details

    • INVALID_SCHEDULE_MESSAGE

      public static final String INVALID_SCHEDULE_MESSAGE
      The account's one sentence for every malformed schedule.
      See Also:

    • NEVER_FIRES_MESSAGE

      public static final String NEVER_FIRES_MESSAGE
      The sentence for a well-formed expression that names no instant at all, such as February 31st.
      See Also:

  • Method Details

    • parse

      public static CronSchedule parse(String schedule)
      Parse a whole USING CRON … schedule, refusing with the account's sentences.
      Parameters:
      schedule - the SCHEDULE text, USING CRON included
      Returns:
      the parsed schedule

    • zone

      public ZoneId zone()
      The zone the fields are read in.

    • nextFireAfter

      public ZonedDateTime nextFireAfter(ZonedDateTime from)
      The first whole minute strictly after from that the schedule names, read in the schedule's own zone.
      Parameters:
      from - the instant to search after
      Returns:
      the next fire, or null when none exists within the search window — which means none ever will