Article

Jakarta EE: Creating an Enterprise JavaBeans timer

December 13, 2019
Java
Rhuan Rocha
Technical Support Engineer
Enterprise JavaBeans

Enterprise JavaBeans (EJB) has many interesting and useful features, some of which I will be highlighting in this and upcoming articles. In this article, I'll show you how to create an EJB timer programmatically and with annotation. Let's go!

The EJB timer feature allows us to schedule tasks to be executed according a calendar configuration. It is very useful because we can execute scheduled tasks using the power of Jakarta context. When we run tasks based on a timer, we need to answer some questions about concurrency, which node the task was scheduled on (in case of an application in a cluster), what is the action if the task does not execute, and others. When we use the EJB timer we can delegate many of these concerns to Jakarta context and care more about business logic. It is interesting, isn't it?

Creating an EJB timer programmatically

We can schedule an EJB timer to runs according to a business logic using a programmatic approach. This method can be used when we want a dynamic behavior, according to the parameter values passed to the process. Let's look at an example of an EJB timer: 

import javax.annotation.Resource;
import javax.ejb.SessionContext;
import javax.ejb.Stateless;
import javax.ejb.Timeout;
import java.util.logging.Logger;

@Stateless
public class MyTimer {

    private Logger logger = Logger.getLogger(MyTimer.class.getName());
    @Resource
    private SessionContext context;

    public void initTimer(String message){
        context.getTimerService().createTimer(10000, message);
    }

    @Timeout
    public void execute(){
        logger.info("Starting");

        context.getTimerService().getAllTimers().stream().forEach(timer -> logger.info(String.valueOf(timer.getInfo())));
        

        logger.info("Ending");
    }    
}

To schedule this EJB timer, call this method: 

@Inject
private MyTimer myTimer;
....
myTimer.initTimer(message);

After passing 10000 milliseconds, the method annotated with @Timeout will be called.

Scheduling an EJB timer using annotation

We can also create an EJB timer that is automatically scheduled to run according to an annotation configuration. Look at this example: 

@Singleton
public class MyTimerAutomatic {

    private Logger logger = Logger.getLogger(MyTimerAutomatic.class.getName());

    @Schedule(hour = "*", minute = "*",second = "0,10,20,30,40,50",persistent = false)
    public void execute(){

        logger.info("Automatic timer executing");

    }
}

As you can see, to configure an automatic EJB timer schedule, you can annotate the method using @Schedule and configure the calendar attributes. For example: 

@Schedule(hour = "*", minute = "*",second = "0,10,20,30,40,50",persistent = false)

As you can see, the method execute is configured to be called every 10 seconds. You can configure whether the timer is persistent as well.

Conclusion

EJB timer is a good EJB feature that is helpful in solving many problems. Using the EJB timer feature, we can schedule tasks to be executed, thereby delegating some responsibilities to Jakarta context to solve for us. Furthermore, we can create persistent timers, control the concurrent execution, and work with it in a clustered environment.  If you want to see the complete example, visit this repository on GitHub.

Last updated: July 1, 2020

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