@Override
 public void printReferencesById(List<Long> referenceIds) {
   for (Long referenceId : referenceIds) {
     Reference reference = referenceDAO.findById(referenceId);
     reference.setState(Reference.ReferenceState.PROCESSED);
     referenceDAO.update(reference);
   }
 }
 @Override
 public void readyReferencesById(List<Long> referenceIds) {
   for (Long referenceId : referenceIds) {
     Reference reference = referenceDAO.findById(referenceId);
     reference.setState(Reference.ReferenceState.READY);
     referenceDAO.update(reference);
   }
 }
 @Override
 public void issueReferencesById(List<Long> referenceIds) {
   for (Long referenceId : referenceIds) {
     Reference reference = referenceDAO.findById(referenceId);
     reference.setIssuedDate(new Date());
     reference.setState(Reference.ReferenceState.ISSUED);
     referenceDAO.update(reference);
   }
 }
 @Override
 public void removeReferencesById(List<Long> referenceIds) {
   for (Long referenceId : referenceIds) {
     referenceDAO.deleteById(referenceId);
   }
 }
 @Override
 public void registrationReference(Reference reference) {
   reference.setRegisteredDate(new Date());
   reference.setState(Reference.ReferenceState.REGISTERED);
   referenceDAO.saveOrUpdate(reference);
 }