In getUserById you shouldn't create a new object (user1) which isn't used. Just assign it to the already (but null) initialized user. Otherwise Hibernate.initialize(user); is actually Hibernate.initialize(null);
Here's the new getUserById (I haven't tested this ;)):
public User getUserById(Long user_id) {
Session session = null;
Object user = null;
try {
session = HibernateUtil.getSessionFactory().openSession();
user = (User)session.load(User.class, user_id);
Hibernate.initialize(user);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (session != null && session.isOpen()) {
session.close();
}
}
return user;
}