Job Scheduling

There are multiple ways to schedule a job:

1. Spring in built- Task scheduler
2. Quartz [Third party open source frame work ]
3. Timer that comes as integrated wih JDK 1.3

Spring + Quartz integration 

1. Quartz JobDetail objects contain all information needed to run a job. Spring provides a JobDetailFactoryBean 
2. The timeout is specified in the job data map. The job data map is available through the JobExecutionContext (passed to you at execution time), but the JobDetail also gets its properties from the job data mapped to properties of the job instance. 
3. Often you just need to invoke a method on a specific object. Using the MethodInvokingJobDetailFactoryBean you can do exactly this:
4. By default, Quartz Jobs are stateless, resulting in the possibility of jobs interfering with each other. If you specify two triggers for the same JobDetail, it might be possible that before the first job has finished, the second one will start. If JobDetail classes implement the Stateful interface, this won’t happen. The second job will not start before the first one has finished. To make jobs resulting from the MethodInvokingJobDetailFactoryBean non-concurrent, set the concurrent flag to false.
5. Finally we wireup jobs & triggers using SchedulerFactoryBean

References:

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https://docs.spring.io/spring/docs/current/spring-framework-reference/integration.html#scheduling-quartz

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TaskScheduler

public interface TaskScheduler {

    ScheduledFuture schedule(Runnable task, Trigger trigger);
    ScheduledFuture schedule(Runnable task, Date startTime);
    ScheduledFuture scheduleAtFixedRate(Runnable task, Date startTime, long period);
    ScheduledFuture scheduleAtFixedRate(Runnable task, long period);
    ScheduledFuture scheduleWithFixedDelay(Runnable task, Date startTime, long delay);
    ScheduledFuture scheduleWithFixedDelay(Runnable task, long delay);

}

Spri




@EnableScheduling. This annotation enables Spring’s scheduled task execution capability, similar to functionality found in Spring’s task namespace we saw in previous tutorial. Thanks to @EnableScheduling, all the bean methods annotated with @Scheduler will be registered for scheduling

Above @Scheduled annotated method will be called by Scheduler every 5 seconds. Note that the method which is annotated with @Scheduler must return void and must not have any parameters. Of course you can inject another bean in above bean to get some external functionality called in printMessage.

@Scheduled annotation have several attributes to specify different scheduling timelines. initialDelay attribute specifies the number of milliseconds to wait before the first execution of the method. fixedRate specifies the number of milliseconds between each method start , regardless of how long method takes to complete. fixedDelay specifies the number of milliseconds between completion of previous run, and start of next run.
Attribute cron provides more fine-grained control on task execution scheduling. For example, @Scheduled(cron=*/5 * * * * MON-FRI") configures this method to be executed every 5 seconds but only on weekdays.

Spring  has its own scheduler then why quartz is still relevant ?

• http://www.baeldung.com/spring-quartz-schedule
•  http://khalidsaleem.blogspot.com/2015/03/quartz-scheduler-vs-spring-scheduler.html
• https://stackoverflow.com/questions/4385719/spring-scheduling-scheduled-vs-quartz

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