Using primary key from a sequence on hibernate

How can a use primary key in hibernate from a Postgres sequence? I need the primary be autogenerated, and them how i can get the sequence value for use in Hibernate

this is my code

Mapped class

import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.SequenceGenerator;
import javax.persistence.Table;
import javax.persistence.Temporal;

@Entity
@Table(name="ensaio")
public class Ensaio implements Serializable {

  @Id
  @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="ensaio_seq")
  @SequenceGenerator(name="ensaio_seq", sequenceName="ensaio_seq")
  @Column(name="ensaio_id")
  private long id;
  private String nome;
  @Column(nullable=false)
  private String modelo;
  private String site;
  @Temporal(javax.persistence.TemporalType.DATE)
  private Date datadoensaio;
  private int qtdeFotos;
  private String fotografo;

  getter and setters...
}

My DAO:

import java.util.List;
import model.Ensaio;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import util.hibernate.HibernateUtil;

public class HEnsaioDAO {

  private Session session;
  private SessionFactory sessionFactory = HibernateUtil.getSessionFactory();

  public HEnsaioDAO() {
    session = sessionFactory.openSession();
  }

  public List<Ensaio> findAll(){
    Query query = session.createQuery("from Ensaio");
    return query.list();
  }

  public void insertEnsaio(Ensaio ensaio){
    session.save(ensaio);
  }

  //testing insertion
  public static void main(String[] args) {
    Ensaio e = new Ensaio();
    e.setModelo("Roberta Maria");
    e.setSite("dsestudio");
    e.setFotografo("Jose Sobrero");
    e.setNome("Dama das camelias");

    HEnsaioDAO dao = new HEnsaioDAO();

    dao.insertEnsaio(e);


    List<Ensaio> list = dao.findAll();
    for (Ensaio ensaio : list) {
      System.out.println(ensaio.getModelo());
      System.out.println(ensaio.getNome());
      System.out.println(ensaio.getFotografo());
    }
  }

}

Nothing happens in database (Postgres 8.3). What wrong? Thanks