Avoid Quartz creating new instance every time

Question

Quartz is creating new instance of the class through the JobBuilder each time

JobBuilder.newJob(MyJob.class)

However, I only want one MyJob instance, and only trigger testFunction from execute function, how can I make it work?

I find through QuartzGuiceLib I can use some annotations to make it happen, through Spring I can change something in configuration file. But how can I implement it by pure Java without any framwork?

Below is the code snapshot:

public class MyJob implements Job {
    public MyJob() {
        testFunction();

        try {
            final Scheduler scheduler = StdSchedulerFactory.getDefaultScheduler();
            if (!scheduler.checkExists(JOB_KEY)) {
                triggerScheduler(scheduler);
            } else {
                log.info("Job with key {{}} already exist", JOB_KEY);
            }
        } catch (SchedulerException e) {
            log.error("Fail to start scheduler", e);
        }
    }

    public void testFunction() {
    }

    private void triggerScheduler(final Scheduler scheduler) throws SchedulerException {
        final JobDetail jobDetail = JobBuilder.newJob(MyJob.class)
                .withIdentity(JOB_KEY)
                .build();

        final Trigger trigger = TriggerBuilder.newTrigger()
                .withIdentity("myjob")
                .withSchedule(
                        simpleSchedule()
                                .withIntervalInSeconds(60)
                                .repeatForever())
                .build();

        scheduler.start();

        log.info("Scheduling job with key {{}}", jobDetail.getKey());

        scheduler.scheduleJob(jobDetail, trigger);
    }

    @Override
    public void execute(JobExecutionContext context) throws JobExecutionException {
        testFunction();
    }
}

Answer 1

It might be easier to keep the job and scheduler in two separate classes as below:

public class MyQuartzScheduler {
    public static void main( String[] args ) throws Exception {
        JobDetail job = JobBuilder.newJob(MyJob.class)
        .withIdentity("dummyJobName", "group1").build();

        Trigger trigger = TriggerBuilder
        .newTrigger()
        .withIdentity("MyJobTrigger", "group1")
        .withSchedule(
            CronScheduleBuilder.cronSchedule("0 * * * * ?"))
        .build();

        Scheduler scheduler = new StdSchedulerFactory().getScheduler();
        scheduler.start();
        scheduler.scheduleJob(job, trigger);
    }
}

And then your Job Class:

public class MyJob implements Job {    
    public void testFunction() {
        System.out.println("Running Test!");
    }

    @Override
    public void execute(JobExecutionContext context) throws JobExecutionException {
        testFunction();
    }
}

This is an adaptation taken from an mkyong tutorial article found at:

https://www.mkyong.com/java/quartz-2-scheduler-tutorial/

For the answer to your question though, Quartz does create a new instance per run: https://stackoverflow.com/a/10463309/1410671

You could make another static class or Factory that your Job class would call which would use the same instance every call.

public class MyJob implements Job {

    public void testFunction() {
        MyClassWithStaticCounter.increaseCounter(1);
        System.out.println(MyClassWithStaticCounter.getCounter());
    }

    @Override
    public void execute(JobExecutionContext context) throws JobExecutionException {
        testFunction();
    }
}

And your class that has the static stuff:

public class MyClassWithStaticCounter {
    private static int counter = 0;

    public static void increaseCounter(int i){
        counter += i;
    }

    public static int getCounter(){
        return counter;
    }
}