mám dataTable svázaný s vector proměnnou, takže do ní tahám data přes  public Vector
managed bean:
<Room> getAllRooms() {
        if(allRooms == null){
            allRooms = roomSBLocal.GetAllRooms();
        }
        return allRooms;
    }
session bean:
 @Override
    public Vector<Customer> GetAllCustomers() {
         Vector<Customer> customers = getCustomerDAO().GetAllCustomers();
        return customers;
    }

DAO:
public static String QUERY_SELECT_ALL_CUSTOMERS = "SELECT c FROM Customer c";

@Override
    public Vector<Customer> GetAllCustomers() {
        return (Vector<Customer>)em.createQuery(QUERY_SELECT_ALL_CUSTOMERS).getResultList();
    }