Scheduled database maintenance with Java EE 6 (connection lifetime)

Question

I'm new to Java EE 6 so I apologize if the answer to this question is obvious. I have a task that must run hourly to rebuild a Solr index from a database. I also want the rebuild to occur when the app is deployed. My gut instinct is that this should work:

@Singleton
@Startup
public class Rebuilder {
  @Inject private ProposalDao proposalDao;
  @Inject private SolrServer  solrServer;

  @Schedule(hour="*", minute="0", second="0")
  public void rebuildIndex() {
    // do the rebuild here
  }
}

Since I'm using myBatis, I have written this producer:

public class ProposalSessionProvider {
  private static final String CONFIGURATION_FILE = "...";

  static {
    try {
      sessFactory = new SqlSessionFactoryBuilder().build(
        Resources.getResourceAsReader(CONFIGURATION_FILE));
    }
    catch (IOException ex) {
      throw new RuntimeException("Error configuring MyBatis: " + ex.getMessage(), ex);
    }
  }

  @Produces
  public ProposalsDao openSession() {
    log.info("Connecting to the database");
    session = sessFactory.openSession();
    return session.getMapper(ProposalsDao.class);
  }
}

So I have three concerns:

1. What's the appropriate way to trigger a rebuild at deployment time? A @PostConstruct method?
2. Who is responsible for closing the database connection, and how should that happen? I'm using myBatis which is, I believe, pretty ignorant of the Java EE lifecycle. It seems like if I use @Singleton the connections will never be released, but is it even meaningful to put @Startup on a @Stateless bean?
3. Should the Rebuilder be a singleton or not? It seems like if it is not I couldn't use @PostConstruct to handle the initial rebuild or I'll get double rebuilds every hour.

I'm not really sure how to proceed here. Thanks for your time.

Answer 1

I don't know myBatis but i can tell you than @Schedule job is transactional. Anyway i'am not sure that JTA managed transaction will apply here according to the way you retrieve the session.
Isn't there a way to retrieve a persistenceContext in MyBatis ?

For the trigger part IMHO @Startup will do the job properly and will need a singleton bean so. Anyway i'am not able to tell you which of the 2 methods you propose is the best one.