@Scheduled로 작업 예약

Many applications need work to run periodically: cleaning up data, sending digests, refreshing caches. Spring provides scheduling without an external job framework.

Add @EnableScheduling to a configuration class to activate Spring's scheduler.

The fixedRate option runs a method every N milliseconds, measured from the start of each run.

fixedDelay waits N milliseconds after the previous run finishes, preventing overlap when a task takes a while.

Use fixedRate for steady cadence and fixedDelay when each run must fully complete before the next begins. Choosing wrong can cause overlapping executions.

For calendar-based timing use cron. The expression has six fields: second, minute, hour, day, month, weekday.

0 0 2 * * * means at second 0, minute 0, hour 2, every day, every month, any weekday, that is, 2 AM daily.

The initialDelay attribute postpones the first execution, useful for letting the app warm up before background work begins.

By default a single thread runs all scheduled tasks. A long task can delay others, so configure a thread pool or pair scheduling with @Async for heavy work.

If you run multiple instances, each will fire the same schedule. Use a distributed lock (for example ShedLock) to ensure a job runs once across the cluster.

Put the cron expression in properties so you can change timing per environment without recompiling.

Test your understanding of scheduled tasks.

You enabled scheduling and used fixedRate, fixedDelay, cron expressions, and initial delays. You also learned to externalize schedules and to coordinate jobs safely across a cluster.