[transaction] org.hibernate.HibernateException: createQuery is not valid without active transaction

public boolean checkUserExistsWithName(String username) {
  SessionFactory sf = HibernateUtil.getSessionFactory();
  Session s = sf.getCurrentSession();
  s.beginTransaction();
  long count = (Long)s.createQuery("select count(*) from User u where u.username=:username").setString("username",username).uniqueResult();
  s.getTransaction().commit();
  if(count>0){
   return true;
  }
  return false;
 }

我的是因为  s.beginTransaction();忘记开启导致。