SessionFactory Object

The SessionFactory is a heavyweight object; it is usually created during application start up and kept for later use. You would need one SessionFactory object per database using a separate configuration file. So, if you are using multiple databases, then you would have to create multiple SessionFactory objects.

Session Object

A Session is used to get a physical connection with a database. The Session object is lightweight and designed to be instantiated each time an interaction is needed with the database. Persistent objects are saved and retrieved through a Session object.

The session objects should not be kept open for a long time because they are not usually thread safe and they should be created and destroyed them as needed.

Example

public class BasicUtil {
    private static final SessionFactory sessionFactory;

    static {
        try {
            sessionFactory = new Configuration()
                    .configure()
                    .buildSessionFactory();
        } catch (Throwable ex) {
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static Session getSession() throws HibernateException {
        return sessionFactory.openSession();
    }

    public static void main(String... args){
        Session session = getSession();
        session.beginTransaction();
        Student s = new Student(1,"Ram", 25, Calendar.getInstance());
        session.save(s);
        session.getTransaction().commit();
    }
}