Thursday, June 9, 2011

Scheduling: Using Quartz (Enterprise Job Scheduler)


Before you can use the scheduler, it needs to be instantiated (who'd have guessed?). To do this, you use a SchedulerFactory. Some users of Quartz may keep an instance of a factory in a JNDI store, others may find it just as easy (or easier) to instantiate and use a factory instance directly (such as in the example below).

Once a scheduler is instantiated, it can be started, placed in stand-by mode, and shutdown. Note that once a scheduler is shutdown, it cannot be restarted without being re-instantiated. Triggers do not fire (jobs do not execute) until the scheduler has been started, nor while it is in the paused state.

Here's a quick snippet of code, that instantiates and starts a scheduler, and schedules a job for execution:
SchedulerFactory schedFact = new org.quartz.impl.StdSchedulerFactory();

  Scheduler sched = schedFact.getScheduler();

  sched.start();

  // define the job and tie it to our HelloJob class
  JobDetail job = newJob(HelloJob.class)
      .withIdentity("myJob", "group1")
      .build();
        
  // Trigger the job to run now, and then every 40 seconds
  Trigger trigger = newTrigger()
      .withIdentity("myTrigger", "group1")
      .startNow()
      .withSchedule(simpleSchedule()
          .withIntervalInSeconds(40)
          .repeatForever())            
      .build();
        
  // Tell quartz to schedule the job using our trigger
  sched.scheduleJob(job, trigger);