@Scheduled add Support for Default Value and for Switching Timer Off

Description

The @Scheduled annotation currently allows the attributes cron, every and delayed to contain a fix value or reference a property value by an expression {propertyname}. I suggest to offer a default value for the property expression: e.g. @Scheduled(every = "{mytask.interval:5m}") -> If the property mytask.intevalis null then the default value 5m is used. Also it is sometimes helpful to be able to switch a specific job off (e.g. on specific nodes). I suggest that if the property expression results in offor disabled, the timer for that scheduled task is switched off: @Scheduled(every = "{mytask.interval:5m}") if mytask.inteval is off the task will not be scheduled.

More examples: mytask.interval=null: @Scheduled(every = "{mytask.interval:off}") -> disabled mytask.interval=off: @Scheduled(every = "{mytask.interval:5m")} -> disabled mytask.interval=null: @Scheduled(every = "{mytask.interval:5m}") -> scheduled every 5m mytask.schedule=off: @Scheduled(cron = "{mytask.schedule:0/2 0/2 0 ? * * *")} -> disabled

mytask.delayed=null: @Scheduled(every= "5m", delayed = "{mytask.delayed:1m}") -> scheduled every 5m with an initial delay of 1m.

• all String attributes of the @Scheduled annotation should support null defaults (similar to Wildfly property-replacement)
• cronand every should support the reserved values off and disabled to disable scheduling. (Better solution than: https://stackoverflow.com/questions/13835221/quartz-cron-expression-that-will-never-execute for cron and every cannot be switched off yet)
• Besides of the current property expression the JBoss/Wildfly style ${property} expression could be supported, too
• Optionally nested expressions could be supported: @Scheduled(every = "{mytask.interval:{global.defaultInterval:off}})
• Optionally property substitution could be used for substrings: mytask.minutes='15,30,45': @Scheduled(cron = "0 {mytask.minutes} * ? * *") -> cron = 0 15,30,45 * ? * *

Implementation ideas

As property expressions are a general feature. This should probably be implemented consistently by different extensions. The current implementation is located in io.quarkus.scheduler.runtime.util.SchedulerUtils and only supports a single property value lookup.

[mkouba]

So should we prevent: delay="${myconf.delay}s"or every="${myconf.task1.interval:${myconf.default.interval:off}}" ?

Well, I don’t think we need to prevent this. We could just mention that the syntax follows the SM expression rules, add a link, and only show the simple examples, i.e. ${my.conf.delays:10s} or {my.conf.delays:off}.

[radcortez]

Let me know if you need help.