Hibernate 4.2 SynchronF方法中的SessionFactory

Question

我正在使用Hibernate 4.2.21，在几篇文章中我看到有些人在方法中使用Synchronized来创建Hibernate的Session Factory，我的问题是关于什么是最佳实践，有或没有？从我的角度来看，我认为如果我们将变量定义为静态，则同步没有意义..

public class HibernateSessionFactory {

    private static SessionFactory sessionFactory = buildSessionFactory();

    private static final Logger logger = LogManager.getLogger(HibernateSessionFactory.class);

    private HibernateSessionFactory() {}

    private static synchronized SessionFactory buildSessionFactory() {

        Configuration configuration = new Configuration();
        SessionFactory sf = null;

        try {

            configuration.configure("hibernate.cfg.xml");


            configuration.setProperty("hibernate.dialect", System.getProperty("myApp.db.dialect"));
            configuration.setProperty("hibernate.connection.driver_class", System.getProperty("myApp.db.driver"));
            configuration.setProperty("hibernate.connection.datasource", System.getProperty("myApp.db.jndi"));

            if (sessionFactory == null) {
                ServiceRegistry serviceRegistry = new ServiceRegistryBuilder().applySettings(configuration.getProperties()).buildServiceRegistry();
                sf = configuration.buildSessionFactory(serviceRegistry);
            }

            return sf;

        } catch (HibernateException ex) {
            logger.error("Init SessionFactory creation failed: ", ex);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static void shutdownSessionFactory() {

      if(!sessionFactory.isClosed()){
        sessionFactory.close();
        logger.info("Session Factory shutdown");
      }else{
        logger.info("Session Factory is already closed");
      }

    }

}