Scheduled in SpringBoot

Schedule#

Sometimes it is necessary to use timing functions to implement certain features. For example, sending emails or notifications at a specific time.

In this case, the Scheduled annotation is needed.

Enabling Schedule in SpringBoot#

First, add the @EnableScheduling annotation to the startup class.
Create a component.
Write the schedule method and add the @Scheduled annotation.

For example:

@Component
public class TestSchedule {
    Logger logger = LoggerFactory.getLogger(TestSchedule.class);

    @Scheduled(cron = "0 * * * * *")
    public void testCommon(){
        logger.info("common "+Instant.now().toString());
    }

    @Scheduled(fixedDelay = 1000)
    public void testFixDelay(){
        logger.info("delay "+Instant.now().toString());
    }

    @Scheduled(initialDelay = 1000,fixedDelay = 1000)
    public void testInitDelay(){
        logger.info("delay "+Instant.now().toString());
    }

    @Scheduled(fixedRate = 2000)
    public void testRateDelay(){
        logger.info("rate "+Instant.now().toString());
    }
}

Configuration of Annotations#

First type, scheduled tasks#

The first type is scheduled tasks, where the cron value in @Scheduled is added with an expression to indicate when the method should be executed.

cron-like expression#

The expression is generally in the format: * * * * * * *.

There are a total of 7 positions, and the last one can be left blank, which means it can be set with only 6 positions.

From left to right, the order is: seconds, minutes, hours, day of the month, month, day of the week, ~~year~~.

Their values are respectively:

0-59 seconds
0-59 minutes
0-23 hours
1-31 day of the month
1-12 month
1-7 day of the week
1970-2099 year

Examples#

0 * * * * ? means triggering every time the seconds reach 0, i.e., every minute.

0 0 * * * ? means triggering every time the minutes reach 0, i.e., every hour. It can also be written as * 0 * * * *.

* * 3 * * ? means executing at 3 o'clock every day.

* * 3 15 * ? means executing at 3 o'clock on the 15th day of each month. The question mark represents uncertainty or flexibility because day of the week and day of the month conflict with each other.

* * 3 ? * 1 means executing at 3 o'clock every Monday. The corresponding day is represented by a question mark.

* * 3-5 * * ? means executing at 3, 4, and 5 o'clock every day. The - represents a range.

There is also the option to use 3,6,9 to represent a list of values, and 2/10 to represent starting from 2 and incrementing by 10.

Delayed tasks#

There are two types of delays: delay after start and delay after completion.

fixedDelay#

fixedDelay represents the delay after the previous execution before the next execution.

fixedRate#

fixedRate represents starting the timer after the previous execution and executing after a certain time.