Java : Quartz scheduler - is there a way I can get next five runs of a scheduled job

问题

Is there any API which gives the next n runs of a cron expression.

回答1:

Quartz jobs are scheduled using a Trigger (org.quartz.Trigger). The trigger interface exposes two useful methods:

Date getNextFireTime();
Date getFireTimeAfter(Date afterTime);

So, take your Trigger, call getNextFireTime(). Now you know when it'll fire next. Then call getFireTimeAfter( next ) and pass it in the next fire time. Repeat until you have enough run times for your use case.

So, for five runs, something like this should work:

List<Date> getNextFiveRuns(Trigger trigger) {
    List<Date> runs = new ArrayList<>();
    Date next = trigger.getNextFireTime();

    // check for null, which indicates a non-repeating trigger or one with an end-time
    while(next != null && runs.size() < 5) {
      runs.add(next);
      next = trigger.getFireTimeAfter(next);
    }
    return runs;
}

Quartz 2.3.0 JavaDoc: org.quartz.Trigger

回答2:

You can calculate next run times like this:

import org.springframework.scheduling.support.CronTrigger;
import org.springframework.scheduling.support.SimpleTriggerContext;

public static void main(String[] args) {
    CronTrigger trigger = new CronTrigger("0 0 10 * * ?");
    SimpleTriggerContext triggerContext = new SimpleTriggerContext();
    Date testDate = new Date();
    int i = 0;
    while (i++ < 5) {
        triggerContext.update(null, null, testDate);
        testDate = trigger.nextExecutionTime(triggerContext);
        System.out.println(testDate);
    }
}

And output is:

    Wed Jun 05 10:00:00 CEST 2019
    Thu Jun 06 10:00:00 CEST 2019
    Fri Jun 07 10:00:00 CEST 2019
    Sat Jun 08 10:00:00 CEST 2019
    Sun Jun 09 10:00:00 CEST 2019

回答3:

If you are looking to just understand, you can use http://www.cronmaker.com/ to calculate the next few scheduled run times

Looks like cronmaker has an API as well(I see you have mentioned you are looking for API) :

curl http://www.cronmaker.com/rest/sampler?expression={expression}

Example:

curl http://www.cronmaker.com/rest/sampler?expression=0 0/2 * 1/1 * ? *&hour=13&minute=45

Source:

http://www.cronmaker.com/help/rest-api-help.html

来源：https://stackoverflow.com/questions/56451154/java-quartz-scheduler-is-there-a-way-i-can-get-next-five-runs-of-a-scheduled

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java

spring-boot

quartz