Java(TM) Boutique - Review - Time Management Made Easy with the Quartz Enterprise Job Scheduler

Reviews : Time Management Made Easy with the Quartz Enterprise Job Scheduler :

A Working Example

An example will probably serve to help you understand the features and the architecture better. This simple HelloWorld program demonstrates how simple it is to create a job and schedule it with the Quartz Scheduler. It starts off by defining a HelloWorldJob class and implementing the Job interface. The excecute() method of the class prints Hello World indefinitely:


import org.quartz.*;

public class HelloWorldJob implements Job {
    public void execute (JobExecutionContext context) {
        System.out.println("\nHello World");
        System.out.println
		("This scheduler will continue indefinitely...
		\nHit CTRL+C to exit");
    }
}

import org.quartz.*;
import org.quartz.impl.*;

The following program defines a HelloWorldScheduler and adds the Job, also defining a SimpleTrigger to trigger the job indefinitely:


public class HelloWorldScheduler {
    public static void main(String[] args) {
        try {
            Scheduler scheduler = StdSchedulerFactory.getDefaultScheduler();
            JobDetail jobDetail = new JobDetail
			("Hello World", null, HelloWorldJob.class);
            Trigger trigger = new SimpleTrigger
			("Hello World", "Hello World");
            scheduler.start();
            scheduler.scheduleJob(jobDetail, trigger);
        } catch (SchedulerException schedulerException) {
            schedulerException.printStackTrace();
        }
    }
}

Running the HelloWorldScheduler Sample

To run the HelloWorldScheduler sample, put Quartz.jar and commons-logging.jar in your classpath. Compile the files with:

 
javac HelloWorldScheduler.java

Then run the sample:


java HelloWorldScheduler

After the job has been fired and executed, the scheduler will keep running. Hit Ctrl + C to exit the application.

An Extended Example

The next example sets up a scheduler for an absent-minded guy who keeps forgetting his meals. He needs to set up email reminders every day to remind him to have breakfast, lunch, and dinner. This gentleman has a strict policy of not having any meals on Sundays. Sundays are reserved purely for sleeping.

Note: This example assumes that email API are already present and are accessible to the scheduler.


MealScheduler.java

SchedulerFactory schedulerFactory = new StdSchedulerFactory();
Scheduler scheduler = schedulerFactory.getScheduler();
JobDetail jobDetail = new JobDetail
("MealReminder", "Reminders", Mailer.class);
jobDetail.setDurability(true);
scheduler.addJob(jobDetail, false);

The above code creates an instance of the scheduler. It also creates a JobDetail class to hold the Meal scheduling class and sets its durability to true. The durability has to be set to true if more than one trigger will be associated with the job. Next, add the job to the scheduler using the addJob method. You use this method when you need to add a job to the Scheduler without any triggers associated with it. Now, the job is stored in the Scheduler without any triggers associated with it.


// Create Breakfast Trigger
CronTrigger breakfastTrigger = new CronTrigger
("Breakfast", "Meal Triggers");
breakfastTrigger.setCronExpression("0 0 8 * * ?");
breakfastTrigger.setJobName("MealReminder");
breakfastTrigger.setJobGroup("Reminders");
JobDataMap breakfastMap = new JobDataMap();
breakfastMap.put("mealType", getMealType("morning"));
breakfastMap.put("content", getContent("morning"));
breakfastTrigger.setJobDataMap(breakfastMap);


//Create the Lunch Trigger
CronTrigger lunchTrigger = new CronTrigger
("Lunch", "Meal Triggers");
lunchTrigger.setCronExpression("0 0 12 * * ?");
lunchTrigger.setJobName("MealReminder");
lunchTrigger.setJobGroup("Reminders");
JobDataMap lunchMap = new JobDataMap();
lunchMap.put("mealType", getMealType("noon"));
lunchMap.put("content", getContent("noon"));
lunchTrigger.setJobDataMap(lunchMap);

//Create the Dinner Trigger
CronTrigger dinnerTrigger = new CronTrigger
("Dinner", "Meal Triggers");
dinnerTrigger.setCronExpression("0 0 20 * * ?");
dinnerTrigger.setJobName("MealReminder");
dinnerTrigger.setJobGroup("Reminders");
JobDataMap dinnerMap = new JobDataMap();
dinnerMap.put("mealType", getMealType("night"));
dinnerMap.put("content", getContent("night"));
dinnerTrigger.setJobDataMap(dinnerMap);

The above code demonstrates how triggers can be created for a particular time of day. To schedule the above jobs, you need to associate them with the Scheduler.

Integration with Other Software

Since Quartz is a Java based API, it can be integrated with any J2EE-based API—like JavaMail, JMS, JDBC, etc. It can also be integrated with any third-party API—alleviating a common complaint regarding J2EE. Quartz can also be embedded into an application server by including the Quartz .jar files into the server's classpath.

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