Some applications need to run periodic jobs in the background. On Linux/Unix systems, background processes can be run using the “cronjob” scheduling service. In Java web applications, you can add scheduling to any app in 4 simple steps using Spring and Quartz. This article outlines the steps needed for scheduling, with code snippets required for each step.

Step 1: web.xml

To initialize Spring in your webapp, add this snippet to your web.xml file. If you are already using Spring, you probably already have this in your web.xml.

<!-- Initialize Spring -->
<listener>
 <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

Step 2: applicationContext.xml snippet

There are 3 concepts when configuring your scheduled jobs:

1) The Job: the java code that you want to run in the background periodically

2) A Trigger: a trigger adds scheduling information to your job. There are different types of triggers (e.g. SimpleTrigger, CronTrigger). They differ in the way you specify scheduling information. For example, CronTrigger takes a cronexpression, whereas SimpleTrigger takes a repeatInterval.

3) The Scheduler: this is the actual service which runs in the background and invokes ‘triggers’. You can register multiple triggers with this service.

Add this snippet to your Spring xml file.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN"
 "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>

 <!-- The 'Scheduler': quartz scheduler -->
 <bean id="schedulerFactoryBean" class="org.springframework.scheduling.quartz.SchedulerFactoryBean">
  <!-- list of triggers registered with the scheduler -->
  <property name="triggers">
   <list>
    <!-- Trigger1: JobExample using CronTrigger -->
    <bean id="jobDetailTrigger" class="org.springframework.scheduling.quartz.CronTriggerBean">
     <!-- job class -->
     <property name="jobDetail">
      <bean class="org.springframework.scheduling.quartz.JobDetailBean">
       <!-- CHANGE THIS to the actual implementation class (see step 4)  -->
       <property name="jobClass" value="com.vineetmanohar.example.quartz.JobExample" />
      </bean>
     </property>

     <!-- job schedule: every 5 minutes: CHANGE THIS -->
     <property name="cronExpression" value="0 0/30 * * * ?" />
    </bean>

    <!-- Trigger2: JobExample2 using SimpleTrigger -->
    <bean class="org.springframework.scheduling.quartz.SimpleTriggerBean">
     <property name="jobDetail">
      <bean>
       <!-- CHANGE THIS to the actual implementation class (see step 4)  -->
       <property name="jobClass" value="com.vineetmanohar.example.quartz.JobExample2" />
      </bean>
     </property>

     <!-- wait 4 minutes after startup -->
     <property name="startDelay" value="240000" />

     <!-- every 1 min (60 sec) -->
     <property name="repeatInterval" value="60000" />
    </bean>
   </list>
  </property>
 </bean>

</beans>

Step 3: pom.xml snippet

If you are using Maven, add this to your pom.xml to add Spring and Quartz dependency to your project.

<project>
 <dependencies>
  <dependency>
   <groupId>org.opensymphony.quartz</groupId>
   <artifactId>quartz</artifactId>
   <version>1.6.1</version>
  </dependency>

  <dependency>
   <groupId>org.springframework</groupId>
   <artifactId>spring-context</artifactId>
   <version>2.5</version>
  </dependency>

  <dependency>
   <groupId>org.springframework</groupId>
   <artifactId>spring-context-support</artifactId>
   <version>2.5</version>
  </dependency>
 </dependencies>
</project>

Step 4: Java code snippet

Finally, write the actual implementation. Make sure that job class you specified in step 2 points to this file.

package com.vineetmanohar.example.quartz.JobExample;

import org.quartz.JobExecutionContext;
import org.quartz.JobExecutionException;
import org.springframework.scheduling.quartz.QuartzJobBean;

public class JobExample extends QuartzJobBean {
  protected void executeInternal(JobExecutionContext ctx) throws JobExecutionException {
   System.out.println("Job invoked at : " + new java.util.Date());

   // TODO: implement the job here
 }
}

Cron expression

The format of cron expression is <Seconds> <Minutes> <Hours> <Day-of-Month> <Month> <Day-of-Week> <Year (optional field)>. For example:

Every 30 minutes

0 0/30 * * * ? 

See full reference documentation here.

From http://www.vineetmanohar.com/2010/10/spring-quartz-code-snippets-for-beginners