CODEWITHSUNDEEP
javajakarta-eeejb
Ralph
Ralph

Reputation: 4868

How to implement a permanent background process with EJBs?

I have a question about a general design pattern in EJB. I hava Java EE application (EJBs and Web) and I need a kind of background process which is permanently scanning and processing specific data via JPA.

One solution, I think about, is to implement a @Singleton EJB. In a method annotated with @PostConstruct I can start my process. 

@Singleton
@Startup
public class MyUpdateService {
    @PostConstruct
    void init() {
        while(true) {
            // scann for new data...
            // do the job.....
        }
    }
}

But is this a recommended pattern? Or is there a better way to run such a class in an EJB Container?

In EJBs there are the other patterns like @TimerService and the new Java EE7 batch processing. But both concepts - I think - are used for finite Processes?

Upvotes: 0

Views: 449

Answers (2)

Ralph
Ralph

Reputation: 4868

As an alternative to the TimerSerivce mentioned by @devmind since Java EE 7 it is possible to use the ManagedScheduledExecutorService:

    @Startup
    @Singleton
    public class Scheduler {

        static final long INITIAL_DELAY = 0;
        static final long PERIOD = 2;

        @Resource
        ManagedScheduledExecutorService scheduler;

        @PostConstruct
        public void init() {
            this.scheduler.scheduleAtFixedRate(this::invokePeriodically, 
                    INITIAL_DELAY, PERIOD, 
                    TimeUnit.SECONDS);
        }

        public void invokePeriodically() {
            System.out.println("Don't use sout in prod " + LocalTime.now());
        }

    }

In difference to the TimerSerivce the ExecutorService can be run in parallel in separate tasks. See also a blog post form Adam Bien.

Upvotes: 1

devmind
devmind

Reputation: 364

Using EJB TimerService in current project for tasks like periodic data pruning, or back-end data synchronization. It allows not only single time execution, but also interval timers and timers with calendar based schedule.

Smth like:

@Startup
@Singleton
public class SyncTimer {
    private static final long HOUR = 60 * 60 * 1000L;

    @Resource
    private TimerService timerService;
    private Timer timer;

    @PostConstruct
    public void init() {
        TimerConfig config = new TimerConfig();
        config.setPersistent(false);
        timer = timerService.createIntervalTimer(HOUR, HOUR, config);
    }

    @Timeout
    private synchronized void onTimer() {
        // every hour action
    }
}

Upvotes: 3

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