Integrating and Configuring Hibernate - Beginning Hibernate: From Novice to Professional - page 15

Listing 2-1 is a reprint of Listing 1-4 from the previous chapter, which shows a complete
usage of Hibernate from within an application. The parts of this listing that deal with configu-
ration and integration are highlighted.
Listing 2-1. The Hibernate Approach to Retrieving the POJO
public static List getMessages(int messageId)
throws MessageException
{
SessionFactory sessions =
new Configuration().configure().buildSessionFactory();
Session session = sessions.openSession();
try {
session.beginTransaction();
List list = session.createQuery("from Message").list();
session.getTransaction().commit();
return list;
} catch ( HibernateException e ) {
if ( session.getTransaction() != null )
session.getTransaction().rollback();
log.log(Level.SEVERE, "Could not acquire message", e);
throw new MotdException(
"Failed to retrieve message from the database.",e);
} finally {
session.close();
}
}
As you can see, we called the configure() method on the org.hibernate.cfg.
Configuration class without any arguments. This tells Hibernate to look in the classpath for
the configuration file. The default name for the configuration file is hibernate.cfg.xml —if
you change it, you will need to pass that name explicitly as an argument to the configure()
method. We discuss the configure() method and XML configuration in more detail later in
this chapter.
The configure() method returns an instance of Configuration , which can be used to
obtain a Hibernate SessionFactory instance by calling the buildSessionFactory() method,
as follows:
public SessionFactory buildSessionFactory() throws HibernateException
The SessionFactory is a heavyweight object, and your application should use one
Hibernate SessionFactory object for each discrete database instance that it interacts with.
The SessionFactory relies on the Hibernate configuration properties, which we detail in the
next section of this chapter.
After you have obtained the SessionFactory , you can retrieve Hibernate org.hibernate.
Session objects. While the SessionFactory is a heavyweight object, the Session objects are
lightweight. You perform your persistence operations using Session objects.