Scheduling via Spring

Spring provides support for scheduling activities. One way to do it is using java's Timer class. I created a simple program to display random messages.

publicclass MessageAgent {

publicstaticfinal String[] messages = {
"What the heck !!",
"This is done",
"I quit",
"Great job",
"This rocks"
    };

public String getMessage() {
finalint max = messages.length;
return messages[(int) (max*Math.random())];
    }
}

The class returns a random message on every call. The next step is to create a Task that can be executed by the Scheduler.

publicclass DisplayMsgTask extends TimerTask {

    @Autowired
private MessageAgent displayMessageAgent;
privatefinal SimpleDateFormat dtF = new SimpleDateFormat("hh:mm:ss");

    @Override
publicvoid run() {

        System.out.println(dtF.format(new Date()) + " : "
                + this.displayMessageAgent.getMessage());
    }

}

The next step is to set up a scheduler and schedule the task for execution.

<context:annotation-config/>

<!-- The bean -->
<bean id="displayMessageAgent" class="com.task.MessageAgent"/>

<!-- The task -->
<bean id="displayMessageTask" class="com.task.DisplayMsgTask"/>

<!-- The schedule -->
<bean id="scheduleDisplayMessageTask" class="org.springframework.scheduling.timer.ScheduledTimerTask">
<property name="timerTask" ref="displayMessageTask"/>
<property name="period" value="1000"/><!-- in milliseconds -->
</bean>

<!-- The scheduler -->
<bean class="org.springframework.scheduling.timer.TimerFactoryBean">
<property name="scheduledTimerTasks">
<list>
<ref bean="scheduleDisplayMessageTask"/>
</list>
</property>
</bean>

As can be seen we created a task and scheduled it to execute every 1 second. The next bean is the timer. It will run all the scheduled tasks.
I created a Client to start the Spring Container (and thereby the Scheduler)

publicclass Client {
publicstaticvoid main(String[] args) throws FileNotFoundException {
final ApplicationContext applicationContext = new ClassPathXmlApplicationContext(
"spring-tasks.xml");
System.out.println("Starting the context - " + applicationContext);
    }
}

The logs indicate the code execution:

Apr 12, 2012 7:17:41 PM org.springframework.scheduling.timer.TimerFactoryBean afterPropertiesSet
INFO: Initializing Timer
Starting the context - org.springframework.context.support.ClassPathXmlApplicationContext@19c26f5: startup date [Thu Apr 12 19:17:40 IST 2012]; root of context hierarchy
07:17:41 : I quit
07:17:42 : This rocks
07:17:43 : What the heck !!
07:17:44 : I quit
07:17:45 : What the heck !!
07:17:46 : This is done
07:17:47 : I quit
07:17:48 : I quit
07:17:49 : This is done
07:17:50 : Great job

An additional configuration available in the ScheduledTimerTask is the amount of time by which we would like to delay the start of task(for the first run only).

<bean id="scheduleDisplayMessageTask" class="org.springframework.scheduling.timer.ScheduledTimerTask">
<property name="timerTask" ref="displayMessageTask"/>
<property name="period" value="1000"/><!-- in milliseconds -->
<propertyname="delay" value="5000"/><!-- in milliseconds -->
</bean>