Spring Cron Expression Generator

Spring cron vs Unix cron vs Quartz

Most broken schedules come from copying an expression written for a different cron dialect. The three look alike but disagree on field count, day numbering and how the two day fields combine.

Field reference

L means the last day of the month; L-2 is two days before it. 15W is the weekday nearest the 15th (it never crosses into another month). In the day-of-week field FRIL or 5L is the last Friday, and MON#2 is the second Monday.

Common Spring cron examples

Using the expression with @Scheduled

Enable scheduling once with @EnableScheduling on a configuration class, then put the expression on a no-argument method of a Spring bean. Keep the expression in configuration rather than in code so each environment can change or disable it:

@Component
class ReportJob {

    @Scheduled(cron = "${app.jobs.report.cron}", zone = "Asia/Seoul")
    void sendDailyReport() {
        // ...
    }
}

# application.yml
app:
  jobs:
    report:
      cron: "0 0 9 * * MON-FRI"   # "-" disables the job

Things that bite in production

• One thread by default.Spring Boot's scheduler pool has a single thread (spring.task.scheduling.pool.size=1), so a slow job delays every other scheduled method. Raise the pool size or hand long work to an executor.
• Every instance runs the job. With three replicas, a daily email goes out three times. Use a lock such as ShedLock, or run scheduled work in a single dedicated instance.
• Time zone drift. Containers default to UTC. Set zone explicitly instead of relying on the host.
• Daylight saving time. In zones with DST, 02:30 does not exist on the night clocks jump forward, so the run moves to 03:30. When clocks fall back, the repeated hour is ambiguous. The run list above resolves both cases the way java.time does — or avoid the problem by scheduling in UTC.
• Check what is registered. With Spring Boot Actuator, /actuator/scheduledtasks lists every cron task and its expression — useful when a placeholder did not resolve the way you expected.