How spring batch admin is stopping a running job? - spring-batch

Question

How spring batch admin is stopping a running job from the UI .
On the spring batch admin's online documentation i have read the following lines .
"A job that is executing can be stopped by the user (whether or not it
is launchable). The stop signal is sent via the database and once
detected by Spring Batch in whatever process is running the job, the
job is stopped (status moves from STOPPING to STOPPED) and no further
processing takes place."
Does that mean Spring batch admin UI is directly changing the status of job inside the spring batch table ?
UPDATE: I tried executing the below query on the running job .
update batch_job_execution set status="STOPPED" where job_ins
tance_id=19;
The above query is getting updated in the DB but spring batch is not bale to stop the running job.
If anybody has tried this please do share the logic here .

Answer 1

You're confused between Batch Status vs. Exit Status.
What are you doing with that SQL is changed the STATUS to STOPPED
When a job is running you can stop the job from the code. In each step iteration, check their status and if STOPPING its set, then send the step to stop ongoing.
Anyway, what you doing is not elegant. The correct way is explained in Common Batch Patterns -> 11.2 Stopping a Job Manually for Business Reasons
public class FooProcessor implements ItemProcessor<FooIn,FooOut>{
public FooOut process(FooIn foo) throws Exception {
if (sendToStop(item)) {
throw new MyStopException("I need to Stop: " + item);
}
//do my stuff
return new FooOut(foo);
}
}
Another simple way to stop chunk step is return null in the reader. This tells us that no more elements to iterate the reader
public T read() throws Exception {
T item = delegate.read();
if (ifNeedStop(item)) {
return null; // end the step here
}
return item;
}

Answer 2

I investigated the spring batch code.
It seems they update both the version and status of the BATCH_JOB_EXECUTION.
This works for me:
update batch_job_execution set status="STOPPED", version=version+1 where job_instance_id=19;

Answer 3

If you look into the jars of spring batch admin, you can see that in AbstractStep.java(spring-batch admin class) it checks for the status of the Step and Job from Database .
Based on this status it validates step before running it .
This works well for all cases except in chunk, since next step is called after large processing . If you want to implement in it, you can implement your own listener to check status (but it will increase DB hits) .