Wednesday, April 27, 2011

Quartz example

 Quartz is a full-featured, open source job scheduling system that can be integrated with, or used along side virtually any Java Enterprise of stand-alone application. The Quartz Scheduler includes many enterprise-class features, such as JTA transactions and clustering. The following is a list of features available:
  • Can run embedded within another free standing application
  • Can be instantiated within an application server (or servlet container).
  • Can participate in XA transactions, via the use of JobStoreCMT.
  • Can run as a stand-alone program (within its own Java Virtual Machine), to be used via RMI
  • Can be instantiated as a cluster of stand-alone programs (with load-balance and fail-over capabilities)
  • Supoprt for Fail-over
  • Support for Load balancing.
Quartz components

  1. Scheduler Task – Pure Java class, the task you want to schedule. 
  2. Scheduler Job – Get the “Scheduler Task” from “JobDetail” via “task name“, and specify which schedule task (method) to run.
  3. Scheduler JobDetail – Define a “task name” and link it with “Scheduler Job”.
  4. Trigger – When will run your “Scheduler JobDetail”.
  5. Scheduler – Link “JobDetail” and “Trigger” together and schedule it.
Understanding the whole sequence by code.

Prequisities of coding
The following example demonstrates the use of Quartz scheduler from a stand-alone application. Follow these steps to setup the example, in Eclipse.
  1. Download the latest version of quartz from opensymphony.
  2. Make sure you have the following in your class path (project-properties->java build path):
    • The quartz jar file (quartz-1.7.0.jar).
    • Commons logging (commons-logging-1.1.1.jar)
    • Add any server runtime to your classpath in eclipse. This is for including the Java transaction API used by Quartz. Alternatively, you can include the JTA class files in your classpath as follows
      1. Download the JTA classes zip file from the JTA download page.
      2. Extract the files in the zip file to a subdirectory of your project in Eclipse.
      3. Add the directory to your Java Build Path in the project->preferences, as a class directory.

The code components:

1. Scheduler Task

Create a pure Java class, this is the class you want to schedule.
package com.vaani.common;
 
public class RunMeTask 
{
 public void printMe() {
  System.out.println("Run Me ~");
 }
}

2. Scheduler Job

Create a ‘job’ to implement the Quartz Job interface, and also the execute() method. Get the scheduler task from Job Details via “task name”, and specify which schedule task (method) to run.

package com.vaani.common;
 
import java.util.Map;
 
import org.quartz.Job;
import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;
 
public class RunMeJob implements Job
{
 public void execute(JobExecutionContext context)
 throws JobExecutionException {
 
  Map dataMap = context.getJobDetail().getJobDataMap();
  RunMeTask task = (RunMeTask)dataMap.get("runMeTask");
  task.printMe();
 }
}
 
or  

//you can use already defined scheduler tasks like calendar etc..any POJO
public class RunMeJob implements Job
{
 public void execute(JobExecutionContext context)
 throws JobExecutionException {
 
  
System.out.println("Executing job at: " + 
Calendar.getInstance().getTime()
+ " triggered by: " + context.getTrigger().getName());
} }

3. Scheduler JobDetail

Initialize a JobDetail object, link your scheduler job with setJobClass(RunMeJob.class); method, define a task name and put it into Job data map, dataMap.put(“runMeTask”, task);. This “task name” is the only link between your Job and JobDetail.
P.S : job.setName(“runMeJob”) has no special function, just a descriptive name, you can put anything.
RunMeTask task = new RunMeTask();
 
     //specify your sceduler task details
     JobDetail job = new JobDetail();
     job.setName("runMeJob");
     job.setJobClass(RunMeJob.class);
 
     Map dataMap = job.getJobDataMap();
     dataMap.put("runMeTask", task);

4. Quartz Triggers

Quartz triggers are used to define when the Quartz will run your declared scheduler job. There are two types of Quartz triggers :
  • SimpleTrigger – allows to set start time, end time, repeat interval to run yout job.
  • CronTrigger – allows Unix cron expression to specify the dates and times to run your job.
Code snippet – SimpleTrigger
SimpleTrigger trigger = new SimpleTrigger();
     trigger.setName("runMeJobTesting");
     trigger.setStartTime(new Date(System.currentTimeMillis() + 1000));
     trigger.setRepeatCount(SimpleTrigger.REPEAT_INDEFINITELY);
     trigger.setRepeatInterval(30000);
Code snippet – CronTrigger
//configure the scheduler time
     CronTrigger trigger = new CronTrigger();
     trigger.setName("runMeJobTesting");
     trigger.setCronExpression("0/30 * * * * ?");

5. Scheduler

Link the “JobDetail” and “Trigger” together and schedule it.
//schedule it
     Scheduler scheduler = new StdSchedulerFactory().getScheduler();
     scheduler.start();
     scheduler.scheduleJob(job, trigger);


Sample code

SimpleJob:
public class SimpleJob implements Job {
  public void execute(JobExecutionContext context) 
throws JobExecutionException {
    System.out.println("Executing job at: " + Calendar.getInstance().getTime()
+ " triggered by: " + context.getTrigger().getName());
  }
}


Scheduling job with runner:
public class QuartzTest {
  public static void main(String[] args) {
    try {
      //  Get a scheduler instance.
      SchedulerFactory schedulerFactory = new StdSchedulerFactory();
      Scheduler scheduler = schedulerFactory.getScheduler();

      long ctime = System.currentTimeMillis();

      //  Create a trigger.
      JobDetail jobDetail = new JobDetail("Job Detail", 
"jGroup", SimpleJob.class);
      SimpleTrigger simpleTrigger = new SimpleTrigger("My Trigger", "tGroup");
      simpleTrigger.setStartTime(new Date(ctime));
      
      //  Set the time interval and number of repeats.
      simpleTrigger.setRepeatInterval(100);
      simpleTrigger.setRepeatCount(10);
      
      //  Add trigger and job to Scheduler.
      scheduler.scheduleJob(jobDetail, simpleTrigger);
      
      //  Start the job.
      scheduler.start();
    } catch (SchedulerException ex) {
      ex.printStackTrace();
    }
  }
}



Output
Apr 27, 2011 5:20:47 PM org.quartz.simpl.SimpleThreadPool initialize
INFO: Job execution threads will use class loader of thread: main
Apr 27, 2011 5:20:47 PM org.quartz.core.SchedulerSignalerImpl <init>
INFO: Initialized Scheduler Signaller of type: class org.quartz.core.SchedulerSignalerImpl
Apr 27, 2011 5:20:47 PM org.quartz.core.QuartzScheduler <init>
INFO: Quartz Scheduler v.1.7.3 created.
Apr 27, 2011 5:20:47 PM org.quartz.simpl.RAMJobStore initialize
INFO: RAMJobStore initialized.
Apr 27, 2011 5:20:47 PM org.quartz.impl.StdSchedulerFactory instantiate
INFO: Quartz scheduler 'DefaultQuartzScheduler' initialized from default resource file in Quartz package: 'quartz.properties'
Apr 27, 2011 5:20:47 PM org.quartz.impl.StdSchedulerFactory instantiate
INFO: Quartz scheduler version: 1.7.3
Apr 27, 2011 5:20:47 PM org.quartz.core.QuartzScheduler start
INFO: Scheduler DefaultQuartzScheduler_$_NON_CLUSTERED started.
Executing at: Wed Apr 27 17:20:47 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:47 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:47 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger
Executing at: Wed Apr 27 17:20:48 IST 2011 triggered by: My Trigger

References
The Unix cron expression is highly flexible and powerful, you can learn and see many advance cron expression examples in following website.
1. http://en.wikipedia.org/wiki/CRON_expression
2. http://www.quartz-scheduler.org/docs/examples/Example3.html

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