Java - Formulario Netbeans

private void saveButtonActionPerformed(java.awt.event.ActionEvent evt) {

        try {

            entityManager.getTransaction().commit();

            entityManager.getTransaction().begin();

        } catch (RollbackException rex) {

            rex.printStackTrace();

            entityManager.getTransaction().begin();

            List<Base.Pareja> merged = new ArrayList<Base.Pareja>(list.size());

            for (Base.Pareja p : list) {

                merged.add(entityManager.merge(p));

            }

            list.clear();

            list.addAll(merged);

        }

    }