Java Quartz scheduled Job - disallow concurrent execution of Job

Question

I am using a Quartz Job for executing specific tasks.

I am also scheduling its execution in my Main application class and what i am trying to accomplish is not to allow simultaneous instances of this job to be executed.

So the scheduler should only execute the job if its previous instance is finished.

Here is my Job class:

public class MainJob implements Job {

static Logger log = Logger.getLogger(MainJob.class.getName());

@Override
public void execute(JobExecutionContext arg0) throws JobExecutionException {

    GlobalConfig cfg = new GlobalConfig();

    ProcessDicomFiles processDicomFiles = new ProcessDicomFiles();  
    ProcessPdfReportFiles processPdf = new ProcessPdfReportFiles();

    try {

            log.info("1. ---- SCHEDULED JOB -- setStudiesReadyToProcess");
            processDicomFiles.setStudiesReadyToProcess();

            log.info("2. ---- SCHEDULED JOB --- distributeToStudies");
            processDicomFiles.distributeToStudies(cfg.getAssocDir());                

            ...

            //process any incoming PDF file
            log.info("11. ---- SCHEDULED JOB --- processPdfFolder");
            processPdf.processPdfFolder();

        } catch (Exception ex) {
            Logger.getLogger(FXMLDocumentController.class.getName()).log(Level.ERROR, null, ex);
        }

    log.info(">>>>>>>>>>> Scheduled Job has ended .... <<<<<<<<<<<<<<<<<<<<");

    }
}

So in my application's main class i am starting the scheduler:

...
//start Scheduler
    try {             
        startScheduler();
    } catch (SchedulerException ex) {
        log.log(Level.INFO, null, ex);
    }
...

public void startScheduler () throws SchedulerException {

        //Creating scheduler factory and scheduler
        factory = new StdSchedulerFactory();
        scheduler = factory.getScheduler();

        schedulerTimeWindow = config.getSchedulerTimeWindow();

        JobDetailImpl jobDetail = new JobDetailImpl();
        jobDetail.setName("First Job");
        jobDetail.setJobClass(MainJob.class);

        SimpleTriggerImpl simpleTrigger = new SimpleTriggerImpl();
        simpleTrigger.setStartTime(new Date(System.currentTimeMillis() + 1000));
        simpleTrigger.setRepeatCount(SimpleTrigger.REPEAT_INDEFINITELY);
        simpleTrigger.setRepeatInterval(schedulerTimeWindow);
        simpleTrigger.setName("FirstTrigger");

        //Start scheduler
        scheduler.start();
        scheduler.scheduleJob(jobDetail,simpleTrigger);

}

I would like to prevent scheduler from starting a second MainJob instance if another one is still running ...

Answer 1

Just use the @DisallowConcurrentExecution Annotation on top of the Job class.

See this official example or this tutorial about concurrent job execution.

Answer 2

@DisallowConcurrentExecution can do your job but please consider that it would only prevent your class from being run twice on the same node.

Please see @ReneM comment in Quartz 2.2 multi scheduler and @DisallowConcurrentExecution