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Written By : Amit
Title :
Quartz Scheduler Example

Description :
Load on startup
More...

Written By : Amit
Title :
Web Load Test

Description :
Grinder WEB Load Testing Framework
More...

Tags/Keywords : Quartz Scheduler, Quartz Java,Java Scheduler,Quartz cron,Quartz Job,Quartz Example, Scheduler Example, Quartz Scheduler Example, Java Scheduler
Author : Amit
Date (Year/Month/Date): 2010-05-07
Using Quartz as Scheduler for some dummy Job at some
Trigger timmers set in a predefined XML file

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sort of best practice and we DO NOT expect any of our visitor/reader of this page to assume
this as some sort of best practice for any context and should not be using this as it is
without appropriate evaluation.
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We extend our sincerest apologies for the same.



A very simple example using Quartz as a scheduler in a
web application deployed onto Tomcat web server.

Quartz has a Servlet for initialization of scheduler
and it can be loaded on web server startup time by
setting  load-on-startup tag in web.xml file of the
web application.

In this example I shall be adding various pieces of code
to come up with a working code for running a JOB at some
pre-defined time or on some reoccurring triggers.

So we may have to start with a Job and a Trigger, both having
same group, as defined in the related job definition XML file
such as shown below:

example_jobs.xml
....
....
<quartz>
  <job>
    <job-detail>
      <name>example_job</name>
      <group>example_group</group>
      <job-class>example.jobs.ExampleJob</job-class>
    </job-detail>
    <trigger>
      <simple>
        <name>example_trigger</name>
        <group>example_group</group>
        <job-name>example_job</job-name>
        <job-group>example_group</job-group>
        <start-time>2010-05-07 9:35:00 pm</start-time>
      </simple>
    </trigger>
  </job>
</quartz>
....
....

As you might have noticed quartz tag having job tag and trigger
tag within it. Job and Trigger name and group are to be defined.
I have given same name for the group for Job and Trigger.

Job class is having a custom user defined class with public
no-argument constructor, and this implements Job interface
from the Quartz framework.

In this example trigger is a simple type with the start time
as some predefined time for testing this example.

The Job class file is a dummy job with no task other than saying
some sys out println, as shown below:

ExampleJob.java
package example.jobs;

import org.quartz.Job;
import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;

public class ExampleJob implements Job {

  public ExampleJob() {
    System.out.println("This job constructor called...");
  }
  @Override
  public void execute(JobExecutionContext context)
                          throws JobExecutionException {

    System.out.println("inside execute method of example job");
  }
}


I have defined the Quartz specific properties file as quartz.properties

...
...
org.quartz.scheduler.instanceName = ExampleScheduler
org.quartz.scheduler.instanceId = AUTO

org.quartz.threadPool.class = org.quartz.simpl.SimpleThreadPool
org.quartz.threadPool.threadCount = 2

org.quartz.plugin.jobInitializer.class = org.quartz.plugins.xml.JobInitializationPlugin
org.quartz.plugin.jobInitializer.fileName = jobs/example_jobs.xml
org.quartz.plugin.jobInitializer.failOnFileNotFound = true
...
...


So atleast we should have a scheduler instance name with instance id
can be AUTO generated, a simple thread pool with some thread count.

There is a Job Initialization Plugin used as job intializer, that can
take a file name, in this case it is example_jobs.xml file.
and a provision for fail if this file not found.

This web application will not be having any UI interface , so the
Quartz specific servlet will not require any servlet mapping tag,
as shown below the WEB.XML file:

<web-app>
 <servlet>
  <servlet-name>quartz-loader-servlet</servlet-name>
  <servlet-class>
      org.quartz.ee.servlet.QuartzInitializerServlet
  </servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
</web-app>


After placing all the desired JAR file from the Quartz version
1.3.2, in the lib folder of this example, when web server started,
I observed two lines printed out on console as mentioned in the
Example JOB file in the constructor and the execute methods.

One interesting issue I encountered and how I resolve that is 
discussed below:

When I used the standard DOCTYPE definition from Quartz Framework
with the DTD file as the following URL:
http://www.quartzscheduler.org/dtd/job_scheduling_data_1_0.dtd
in the JOB XML file, I encounted an exception while web server
starting up, so I changed it to only "job_scheduling_data_1_0.dtd"
and placed this dtd file in the TOMCAT bin folder. This resolved
the exception at server startup and the ExampleScheduler started
working as expected..

Any person having any other solution to this issue, please share
with me by using following comment section....

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