我应该在DAO层中使用ThreadLocal变量（我使用Hibernate作为ORM）

Question

在这种情况下，ThreadLocal变量有什么好处？我知道ThreadLocal变量用于保证每个线程都拥有它自己的ThreadLocal对象实例，在这种情况下我将为每个用户设置一个Session，但是Hibernate应该保证这个吗？

这是我的代码：

public class HibernateUtil {

private static final SessionFactory SESSION_FACTORY = buildSessionFactory();
private static StandardServiceRegistryBuilder registryBuilder;
private static final ThreadLocal SESSION = new ThreadLocal();

private static SessionFactory buildSessionFactory() {
    try {
        Configuration configuration = new Configuration().configure();
        registryBuilder = new StandardServiceRegistryBuilder().applySettings(configuration.getProperties());
        return configuration.buildSessionFactory(registryBuilder.build());
    } catch(Throwable e) {
        System.err.println("Initial SessionFactory creation failed." + e);
        throw new ExceptionInInitializerError(e);
    }        
}

public static SessionFactory getSessionFactory() {
    return SESSION_FACTORY;
}

public static Session getSession() {
    Session session = (Session) HibernateUtil.SESSION.get();
    if(session == null) {
        session = SESSION_FACTORY.openSession();
        HibernateUtil.SESSION.set(session);
    }
    return session;
}

public static void begin() {
    getSession().beginTransaction();
}

public static void commit() {
    getSession().getTransaction().commit();
}

public static void rollback() {
    try {
        getSession().getTransaction().rollback();
    } catch(HibernateException e) {
        System.out.println("Cannot rollback: " + e);
    }
    try {
        getSession().close();
    } catch(HibernateException e) {
        System.out.println("Cannot close: " + e);
    }
    HibernateUtil.SESSION.set(null);
}

public static void closeSession() {
    getSession().close();
    HibernateUtil.SESSION.set(null);
}

}