How to use SpringBoot to implement a timer

Implementation of timer

Spring boot startup class code, added @EnableScheduling annotation to enable the timer function

@SpringBootApplication   
@EnableScheduling   // 开启定时功能
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class,args);
    }
}

Scheduling task code, the task class needs to be injected into the @Component annotation In the IoC container

@Component
public class TestSchedulingTask {
    // 这个cron表达式代表从0秒开始，每过3秒执行一次。
    @Scheduled(cron = "0/3 * * * * ?")
    public void test(){
        // 大家可以根据公司的业务来实现，更希望是@Autowrite注入service层的接口，业务逻辑写在service层中。
        // 这里测试我就输出当前系统时间了...
        Date date  = new Date(System.currentTimeMillis());
        String rule = "yyyy-MM-dd HH:mm:ss";
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(rule);
        String format = simpleDateFormat.format(date);
        System.out.println(format);
    }
}

, note here that each task method must be annotated with @Scheduled, and the cron expression must be specified.

You can rest assured, and there are also websites that generate cron expressions online. Let’s take a look at the results output by the console.

Detailed explanation of cron expression

cron expression

Field	Range	Allowed characters
Seconds	0-59	,/-*
Minute(minute)	0-59	,/-*
Hour(hour)	0-23	,/-*
Date (day of month)	1-31(need to consider month inconsistency)	,/-*?LW
month	1-12 (the corresponding English abbreviation is also acceptable)	, /-*
day of week	1-7	,/-*?L
年（year）	This thing is basically not used	This thing is basically not used

Allowed characters Explanation:

,: It is an enumeration with multiple values. For example, 5 and 20 in second represent triggers at 5 and 20 seconds.

/: value 1/value 2, value 1 represents the start time, value 2 represents how often, for example, in my case, it triggers every 3 seconds starting from 0 seconds.

-: Range value, from how long to how long.

*: Common to all ranges.

?: Only exists in date and week. If you want to trigger on the 2nd of every month, but if you use * on the week, it will trigger every day, which will cause a bug. So is it necessary? to replace *.

L: means the last, appearing in date and week. For example, using L in date means the last day of the month, and using 3L in week means triggering on the last Wednesday.

W: Indicates working days, used in dates. If 9W is used, it will be triggered directly if the 9th falls on Monday 1-5. If the 9th is a Saturday, it will be triggered on the 8th. If the 9th is a Sunday, it will be triggered on the Monday. The first trigger is trigger number 10.

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