<persistence-unit name="pippoPU" transaction-type="JTA">
<jta-data-source>jdbc/pippo</jta-data-source>

@ManagedBean(name = "xxxxxxx")
@ViewScoped
public class MioJSFBean implements Serializable {
    .....
    .....

    @Resource
    private UserTransaction utx = null;

    @PersistenceUnit(unitName = "pippoPU")
    private EntityManagerFactory emf = null;

    ....
    ....
}

[ERROR] The server cannot create an EntityManagerFactory factory