NullPointerException using Quartz rescheduler function

Question

I am new to Quartz API and currently using quartz version 2.2.x to create a scheduler class object in java to support my school project but encountered null pointer exception with scheduler.rescheduleJob(trigger.getKey(), cronTrigger); at rescheduleCron function. I am trying to setup a function to accept cron expression to reschedule quartz jobs and have no idea what I am doing wrong. Please help me to rectify this error.

public class quartzScheduler {

public JobDetail job;
public Trigger trigger;
public Scheduler scheduler;

public void quartzScheduler() throws SchedulerException,InterruptedException
{
    job = JobBuilder.newJob(quartzJob.class)
            .withIdentity("quartzJob", "group1").build();

    trigger = TriggerBuilder
            .newTrigger()
            .withIdentity("quartzTrigger", "group1")
                            .startAt(futureDate(1, IntervalUnit.HOUR))
            .withSchedule(
                    SimpleScheduleBuilder.simpleSchedule()
                            .withIntervalInHours(1).repeatForever())
            .build();

    scheduler.start();
    scheduler.scheduleJob(job, trigger);
}

    public void rescheduleCron(String cronExpression) throws SchedulerException
    {
        Trigger cronTrigger = TriggerBuilder
            .newTrigger()
            .withIdentity("quartzTrigger", "group1")
            .withSchedule(cronSchedule(cronExpression))
            .build();

        scheduler.rescheduleJob(trigger.getKey(), cronTrigger);    
    }


public static void main(String[] args) 
{
    quartzScheduler sch= new quartzScheduler(); 
    try {
        sch.rescheduleCron("0 0 * * * ?");
    } catch (SchedulerException ex) {
        Logger.getLogger(quartzScheduler.class.getName()).log(Level.SEVERE, null, ex);
    }
}

Daniel Patrick · Accepted Answer · 2016-05-20T15:48:02.523

In rescheduleCron(), your trigger has not been initialized. It is set to null and when you try to call .getKey() on it, you're getting a NullPointerException.

I see what you're doing... I think you're trying to use quartzScheduler() as a constructor which is why you're expecting the trigger to be initialized. Very small change to fix this: remove the return value from that function. Java constructors do not have return values.

It should look like this:

public class QuartzScheduler {

    public JobDetail job;
    public Trigger trigger;
    public Scheduler scheduler;

    public QuartzScheduler() throws SchedulerException, InterruptedException {
        job = JobBuilder.newJob(quartzJob.class)
                .withIdentity("quartzJob", "group1").build();

        trigger = TriggerBuilder
                .newTrigger()
                .withIdentity("quartzTrigger", "group1")
                .startAt(futureDate(1, IntervalUnit.HOUR))
                .withSchedule(
                    SimpleScheduleBuilder.simpleSchedule()
                .withIntervalInHours(1).repeatForever())
                .build();
        scheduler = new Scheduler(); //maybe do something else here.

        scheduler.start();
        scheduler.scheduleJob(job, trigger);
    }

    public void rescheduleCron(String cronExpression) throws SchedulerException {
        Trigger cronTrigger = TriggerBuilder
            .newTrigger()
            .withIdentity("quartzTrigger", "group1")
            .withSchedule(cronSchedule(cronExpression))
            .build();

        scheduler.rescheduleJob(trigger.getKey(), cronTrigger);    
    }
}

public static void main(String[] args) {
    QuartzScheduler sch= new QuartzScheduler(); 
    try {
        sch.rescheduleCron("0 0 * * * ?");
    } catch (SchedulerException ex) {
        Logger.getLogger(quartzScheduler.class.getName()).log(Level.SEVERE, null, ex);
    }
}

What I've changed:

Capitalized your class name (by convention)
Removed the return values and the exceptions from the constructor
moved the main() call to outside of the class. The main() call uses the class, it is not part of it

Thanks! After trying out your suggestion, I realize I missed out initializing the scheduler too. scheduler = new StdSchedulerFactory().getScheduler(); need to be added before starting the scheduler. — nubbear, May 20 '16 at 15:46
Nice! glad it helped. I've updated the answer to reflect that. — Daniel Patrick, May 20 '16 at 15:48

NullPointerException using Quartz rescheduler function

1 Answers1