While searching for some job scheduler tool, I came across this Open Source tool, called,
Quartz. Most importantly my requirement was to be able to use it from inside an application server like JBoss. After reading some tutorials, I gave it a go. Let me just brief my experience here.
Quick IntroFundamental entities with Quartz or with any other job schedulers are tasks and triggers invoking them. Quartz has got two kinds of triggers: SimpleTriggers and CronTriggers which are very much similar to Unix Cron triggers. There are two ways one can store the jobs in Quartz. RAMJobStore is the most simple one but the tasks stored here do not get persisted, i.e., jobs get forgotten once the server restarts. Other type of job stores are JDBCJobStore. As the name suggests with these job stores, jobs are stored in relational databases. Quartz supports most of the standard databases like MySQL, Oracle and etc. There are two kinds of JDBCJobStores available: JobStoreTX and JobStoreCMT. JobStoreTX is supposed to be used stand alone whereas JobStoreCMT is meant to be used from an application server. As my requirement was to use it with JBoss I used only JobStoreCMT. And, used it with MySQL as the back end database.
Quartz as a JBoss serviceJBoss 4.2.2.GA already has got quartz bundled with it. But actually you can not do much with this as it supports only RAMJobStore. So to use it effectively we need to do some more. We have to copy
quartz-1.6.2.jar and
quartz-jboss-1.6.2.jar in the JBOSS_HOME/server/server_mode/lib directory. Then, we need to create a xml file to configure Quartz as a service in JBOSS_HOME/server/server_mode/deploy directory.
Create the data baseWe need to create the database where all job and trigger information will get stored eventually. The sql scripts are bundled with Quartz download under docs/dbTables directory.
quartz-service.xmlAs already mentioned we need to create the quartz-service file . Let me just enclose a sample file.
<server>
<mbean code="org.quartz.ee.jmx.jboss.QuartzService" name="user:service=QuartzService,name=QuartzService">
<!-- JNDI name for locating Scheduler, "Quartz" is default. -->
<attribute name="JndiName">Quartz</attribute>
<attribute name="Properties">
# Default Properties file for use by StdSchedulerFactory
# to create a Quartz Scheduler Instance, if a different
# properties file is not explicitly specified.
#
# org.quartz.scheduler.classLoadHelper.class =
org.quartz.scheduler.instanceName = DefaultQuartzScheduler
org.quartz.scheduler.rmi.export = false
org.quartz.scheduler.rmi.proxy = false
org.quartz.scheduler.xaTransacted = false
org.quartz.threadPool.class = org.quartz.simpl.SimpleThreadPool
org.quartz.threadPool.threadCount = 5
org.quartz.threadPool.threadPriority = 4
org.quartz.jobStore.class = org.quartz.impl.jdbcjobstore.JobStoreCMT
org.quartz.jobStore.driverDelegateClass = org.quartz.impl.jdbcjobstore.StdJDBCDelegate
org.quartz.jobStore.dataSource = QUARTZ
org.quartz.jobStore.nonManagedTXDataSource = QUARTZ_NO_TX
org.quartz.jobStore.tablePrefix = QRTZ_
org.quartz.dataSource.QUARTZ.jndiURL = java:QuartzDS
org.quartz.dataSource.QUARTZ_NO_TX.driver = com.mysql.jdbc.Driver
org.quartz.dataSource.QUARTZ_NO_TX.URL = jdbc:mysql://localhost:3306/Quartz
org.quartz.dataSource.QUARTZ_NO_TX.user = root
#org.quartz.jobStore.maxMisfiresToHandleAtATime=0
</attribute>
</mbean>
</server>
The point to note here is that we'll need two datasource elements for this configuration. One is standard datasource managed by JBoss container (see the line org.quartz.jobStore.dataSource = QUARTZ) another one is not managed by the container, on which quiatz can call commit/rollback by itself. We have to confugure the container managed datasource as a standard jboss *-ds file, whereas we configure the non_managed_datasource inside this quartz-service.xml itself. Here one gotcha is for the container_managed datasource, we'll need to use XA datasource (I am not very sure why regular local datasource does not work. Maybe reason being Quartz works in a clustered environment, just a guess though). Let me just attach a sample mysqlquartz-ds file here:
<?xml version="1.0" encoding="UTF-8"?>
<datasources>
<xa-datasource>
<jndi-name>QuartzDS</jndi-name>
<xa-datasource-class>com.mysql.jdbc.jdbc2.optional.MysqlXADataSource</xa-datasource-class>
<xa-datasource-property name="URL">jdbc:mysql://localhost:3306/Quartz</xa-datasource-property>
<user-name>root</user-name>
<password></password>
<transaction-isolation>TRANSACTION_READ_COMMITTED</transaction-isolation>
<max-pool-size>5</max-pool-size>
<min-pool-size>0</min-pool-size>
<blocking-timeout-millis>2000</blocking-timeout-millis>
<idle-timeout-minutes>2</idle-timeout-minutes>
<track-connection-by-tx>true</track-connection-by-tx>
<no-tx-separate-pools>false</no-tx-separate-pools>
<exception-sorter-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLExceptionSorter</exception-sorter-class-name>
<!-- <valid-connection-checker-class-name>org.jboss.resource.adapter.jdbc.vendor.MySQLValidConnectionChecker</valid-connection-checker-class-name> -->
<metadata>
<type-mapping>mySQL</type-mapping>
</metadata>
</xa-datasource>
</datasources>
Creating a jobOnce you get the configuration right, other things are pretty simple.
InitialContext ctx = new InitialContext();
Scheduler scheduler = (Scheduler) ctx.lookup("Quartz");
Trigger trigger = TriggerUtils.makeDailyTrigger("myTrigger", 0, 0); //a trigger which gets fired on each midnight
trigger.setStartTime(new Date());
JobDetail job = new JobDetail("jobName", "jobGroup", Executor.class);
job.getJobDataMap().put("Name", "Abdul Sahid Khan");
job.getJobDataMap().put("Age", 125);
scheduler.scheduleJob(job, trigger);
So you get a handle to the Scheduler object using jndi lookup. Remember we set the jndi name in quartz-service.xml file. Then we create a trigger. There is various ways to create a trigger. TriggerUtils is a utils class provided by Quartz itself which gives mane factory methods to create simple triggers. Then we need to create a job. There is no Job class (well, there is an interface by that name but let us now pretend that it does not exist), instead we will create a JobDetail object. While creating JobDetail object we need to provide an Executor class which will be used when this particular job gets fired by the Scheduler. We can store job specific information in the datamap provided by JobDetail object. These information can be used in the Executor class.
Execute the jobThe job gets executed by the class which was passed while creating the JobDetail object. This Executor class needs to implement earlier_ignored Job interface. And that mandates Executor to have a method called
execute().
public class Executor implements Job {
public void execute(JobExecutionContext context) throws JobExecutionException {
String jobName = context.getJobDetail().getName();
String groupName = context.getJobDetail().getGroup();
JobDataMap dataMap = context.getJobDetail().getJobDataMap();
String name = (String) dataMap.get("Name");
Integer age = (Integer) dataMap.get("Age");
logger.info("Job received name: " + jobName + " , Group: " + groupName);
logger.info("Name: " + name + " , Age: " + age);
}
}
Delete the jobTo delete a job we need to know the name and group of the job.
InitialContext ctx = new InitialContext();
Scheduler scheduler = (Scheduler) ctx.lookup("Quartz");
scheduler.deleteJob("jobName", "jobGroup");
Here one must remember that you can not delete a job from inside the execute method, that will create a lock which will cause JVM to crash. So delete should be handled as different process like create.
One last thing about JbossSometime, business logic needs you to have your Executor class inside the your EAR/WAR application. Now that will create a dependency problem while starting the jboss server. Each time Quartz service starts, it tries to recover if there is any misfired jobs. But if Quartz starts before EAR/WAR deploys then we have ClassNotFound problem. To solve this we can use the deploy.last hack given by JBoss. You can create deploy.last directory and put the quartz-service.xml file inside that. That will ensure Quartz service will start after all the application gets deployed.
Reference:
Quartz wiki
