catch java exception in flex

Hi

in my pojo i have one object

@Column(name = "GRUPO", unique = true, nullable = false, length = 45)

public String getGrupo() {
        return this.grupo;
    }

then i have a DAO Class to save object in database like this

public void save(Gruposdeusuarios entity) {
        EntityManagerHelper.log("saving Gruposdeusuarios instance", Level.INFO,
                null);
        EntityManagerHelper.beginTransaction();
        try {
            getEntityManager().persist(entity);
            EntityManagerHelper.commit();
            EntityManagerHelper.log("save successful", Level.INFO, null);           
        } catch (RuntimeException re) {
            EntityManagerHelper.log("save failed", Level.SEVERE, re);
            EntityManagerHelper.rollback();
            throw re;
        }
    }

then i have AbstractAssembler to make a call from flex to dao

public void createItem(Object entity){
        GruposdeusuariosDAO dao = new GruposdeusuariosDAO();
        dao.save((Gruposdeusuarios) entity);
    }

if i duplicate de object i get this exception

GRAVE: save failed
javax.persistence.RollbackException: Exception [TOPLINK-4002] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.DatabaseException
Internal Exception: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry 'ENELDO' for key 'GRUPO'
Error Code: 1062
Call: INSERT INTO mydaniel.gruposdeusuarios (GRUPO) VALUES (?)
    bind => [ENELDO]

the question is

how i can catch the Error Code:1062 and Duplicate Key Name "GRUPO" to flex dataservice on fault to tell flex user it trying to duplicate value

i using Tomcat 6 , Livecycle Data Service 2.5, mysql-connector-java-5.1.8-bin, JPA Toplink and Flex Builder 3.3

Thank