有没有办法在Quartz中模拟触发器失火？ （JAVA）

Question

I'm looking for a way to simulate or force a trigger misfire programatically. Here's the scenario:

I have a job set to trigger but the job requires some underlying resource that may be unavailable at times. If the resource is unavailable, I would like Quartz to re-fire the trigger later based on the misfire policy.

I've explored two options that are similar but not quite what I'm looking for:

1. Throwing a JobExecutionException with refireImmediately set to true: Works, but doesn't delay execution based on misfire policy; this would hammer the resource availability check.
2. Scheduling a second trigger at some fixed interval of time in the future: Also works, but doesn't take into account misfire policy. This means a job could wind up with a bunch of retries queued up stemming from different failed runs.

Any ideas or anything I'm missing? Thanks!

Answer 1

If I got it right, you don't need to force or simulate a misfire because the resource availability is "something your Job can handle" .

Misfires exists and are managed by Quartz for situations like server shutdown or other "unexpected problems" that prevent Job execution.

You have two options to follow to implement a simple fault-tolerance retry logic; your Job can execute it's logic only when the underlying resource is available, so you can:

1. Wait for the resource to become availabile:
   • in this case your job waits and repeat the check for the resource availability, eventually after a short timeout, the job can give up and end.
     
     
2. Just do nothing if the resource is not available:
   • in this case the job ends without doing anything and the it will fire normally and retry according the Trigger definition.

In both cases, if the resource is avaliable, the Job can execute it's inner logic and use the underlying resource. (No misfires, because the Job was actually executed)

This can be done using a Trigger, setting the misfire policy you need in case the Job cannot be executed at all. See This great and detailed article on Quartz misfires.

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In your situation, If you want to execute a job one time every day:

1. Define a Cron trigger that fires multiple times in a day in a given span of time, for exemple, every 15 minutes from 8:00 AM to 12:00 AM:

    0 0/15 8-12 * * ? 

2. Buld a Job that use one of the two approaches described before

3. The first time your Job inner logic executes (that is, the resource is available) your job will save a "job executed flag" with the day of execution somewhere on DB.

On the following trigger executions, the Job will check the flag and will not execute it's inner logic again.

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Also, if your job will take long time to finish, you may want to prevent concurrent execution of the same job using the following annotation on the job implementation:

@DisableConcurrentExecution

See Quartz tutorials for more informations on job execution.