Strict Quartz Cron Validator

Quartz cron expressions explained

Quartz Scheduler is the de-facto job scheduler in the Java / Spring ecosystem, and its cron syntax differs from the classic Unix 5-field cron. Quartz uses 6 mandatory fields plus an optional 7th, and adds several special characters that Unix cron does not have. This validator checks the field count and the allowed values and characters per field.

The fields

In order: seconds minutes hours day-of-month month day-of-week, with an optional year as a 7th field.

• seconds (0-59), minutes (0-59), hours (0-23)
• day-of-month (1-31)
• month (1-12 or JAN-DEC)
• day-of-week (1-7 where 1=SUN..7=SAT, or SUN-SAT)
• year (optional, e.g. 1970-2099)

Special characters

• * — all values in the field.
• ? — "no specific value"; allowed only in day-of-month or day-of-week, and exactly one of those two must be ?.
• - range, , list, / step (e.g. 0/15).
• L — last (last day of month, or last given weekday).
• W — nearest weekday to a given day-of-month.
• # — the nth weekday of the month, e.g. 6#3 = the 3rd Friday (since DOW is 1=SUN..7=SAT, 6=FRI).

Common pitfalls

• Copying a Unix 5-field expression directly — Quartz needs at least 6 fields (it has a leading seconds field).
• Setting both day-of-month and day-of-week to a value, or both to * — exactly one must be ?.
• Assuming Unix day-of-week numbering; in Quartz 1=SUN, not Monday.
• Using ? in a field other than day-of-month / day-of-week.
• Misreading 6#3 as "every 6th and 3rd" — it means the 3rd occurrence of weekday 6.

FAQ

Why does Quartz have a seconds field? Quartz can trigger jobs with second-level precision, so the first field is seconds — that is the main structural difference from Unix cron.

What does 0 0 12 ? * MON-FRI do? It fires at 12:00:00 every Monday through Friday — day-of-month is ? because the schedule is driven by day-of-week.

Is the year field required? No, it is optional. Omit it for a recurring schedule; include it to restrict the trigger to specific years.