Add support for disabled cron expression "-"

[donalmurtagh]

According to the docs, db-scheduler supports

Spring-style cron-expression.

However, a Spring cron expression of "-" means the task will never run, which is useful for disabling a task in a local/test environment.

I tried this expression with db-scheduler, but it caused this exception:

Caused by: java.lang.IllegalArgumentException: Cron expression contains 1 parts but we expect one of [6]
	at com.github.kagkarlsson.shaded.cronutils.parser.CronParser.parse(CronParser.java:120) ~[db-scheduler-10.3.jar:na]
	at com.github.kagkarlsson.scheduler.task.schedule.CronSchedule.<init>(CronSchedule.java:46) ~[db-scheduler-10.3.jar:na]
	at com.github.kagkarlsson.scheduler.task.schedule.CronSchedule.<init>(CronSchedule.java:56) ~[db-scheduler-10.3.jar:na]
	at com.github.kagkarlsson.scheduler.task.schedule.Schedules.cron(Schedules.java:39) ~[db-scheduler-10.3.jar:na]

[kagkarlsson]

Interesting. Yeah, that is not supported. I think I primarily meant that seconds are supported, so I probably should update the doc.

Not sure if it is possible to support that scenario just yet. When we add support for pausing/stopping an execution in db-scheduler, this would be a nice addition

[s-seidel]

We currently use this workaround, which is okay but not perfect:

    @Bean
    Task<Void> triggerCleanUp(final CleanUpService service,
            @Value("${cleanup.cron.expression}") final String cronPattern) {
        if (cronPattern == null || cronPattern.equals("-")) {
            return Tasks.custom("cleanup", Void.class).execute((i, c) -> new OnCompleteRemove<>());
        }
        return Tasks.recurring("cleanup", Schedules.cron(cronPattern)).execute((instance, ctx) -> {
            service.cleanUp();
        });
    }

[donalmurtagh]

This is the workaround that I use. The taskInvitationsSender and autocompleteEventsUpdater beans are jobs that are run by the scheduler.

@Configuration
public class ClusteredSchedulerConfiguration {

    private static final String DISABLED_CRON_EXPRESSION = "-";

    private static final Logger logger = LoggerFactory.getLogger(ClusteredSchedulerConfiguration.class);

    @Bean
    Task<Void> scheduleTaskInvitationsSender(ScheduledTask taskInvitationsSender,
                                             @Value("${cron.task-invitations-sender}") String schedule) {
        return scheduleTask(schedule, taskInvitationsSender);
    }

    @Bean
    Task<Void> scheduleAutocompleteEvents(ScheduledTask autocompleteEventsUpdater,
                                          @Value("${cron.autocomplete-events}") String schedule) {
        return scheduleTask(schedule, autocompleteEventsUpdater);
    }

    private Task<Void> scheduleTask(String cronExpression, ScheduledTask task) {
        boolean isTaskDisabled = DISABLED_CRON_EXPRESSION.equals(cronExpression);

        if (isTaskDisabled) {
            var taskName = task.getTaskName();
            logger.warn("The {} scheduled task is disabled in the current environment", taskName);

            /*
            A workaround for the fact that db-scheduler doesn't support Spring's disabled cron expression
            https://github.com/kagkarlsson/db-scheduler/issues/216

            Return a once-off task that is never scheduled and does nothing when executed
             */
            return Tasks.oneTime(taskName, Void.class).execute((inst, ctx) -> {
            });

        } else {
            Schedule schedule = cron(cronExpression);
            return Tasks.recurring(task.getTaskName(), schedule).execute((instance, ctx) -> task.run());
        }
    }
}

[kagkarlsson]

Hoping this is solved with #286. Does that implementation work for you?

[s-seidel]

Tested and it works well for us.

[kagkarlsson]

Excellent, thanks for the feedback!

[kagkarlsson]

Fixed in 11.2

[donalmurtagh]

@kagkarlsson tested and confirmed it works, thanks very much