上面的代码部分应该是:
private void addEmailAddresses2Student(Integer studentId,
String emailAddress)
{
SessionFactory sessionFactory =
            new Configuration().configure().buildSessionFactory();
Session session = sessionFactory.getCurrentSession();

Transaction tx = session.beginTransaction();

Student student = (Student) session.load(Student.class, studentId);
student.getEmailAddresses().add(emailAddress);

tx.commit();

session.close();
}