Hibernate - Erro na sessao

import java.util.Iterator;

import java.util.List;

import org.hibernate.*;

import org.hibernate.cfg.Configuration;

private SessionFactory factory;
protected Session session;
private int size = 0;
private Amigo[] arrayAmigo = null;

public AmigoDAO() throws Exception {
	HibernateUtil.beginTransaction();
	factory = new Configuration().addClass(Amigo.class)
			.buildSessionFactory();
}

public void insert(Amigo amigo) throws Exception {
	session = HibernateUtil.getSession();
	Session session = factory.openSession();
	session.save(amigo);
	session.flush();
	HibernateUtil.commitTransaction();
	session.close();

}

public Amigo[] List() throws Exception {

	Amigo amigoDTO = null;
	//Amigo[] arrayAmigo = null;
	Session session = factory.openSession();
	session = HibernateUtil.getSession();
	//List amigos = session.createSQLQuery("select {u.*} from amigos
	// {u}","u",Amigo.class).list();
	//Criteria select = session.createCriteria(Amigo.class);
	Query q = session.createQuery("from Amigo a");
	List amigos = q.list();
	//List amigos = select.list();

	int i = 0;
	if (amigos.size() > 0) {
		arrayAmigo = new Amigo[amigos.size()];
		size = amigos.size();
		for (Iterator inter = amigos.iterator(); inter.hasNext();) {
			Amigo am = (Amigo) inter.next();
			amigoDTO = new Amigo();
			amigoDTO.setNome(am.getNome());
			amigoDTO.setCelular(am.getCelular());
			amigoDTO.setEmail(am.getEmail());
			amigoDTO.setEndereco(am.getEndereco());
			amigoDTO.setTelefone(am.getTelefone());
			amigoDTO.setNascimento(am.getNascimento());
			//System.out.println(am.getNome());
			arrayAmigo[i] = amigoDTO;
			i++;
		}
	}

	session.flush();
	HibernateUtil.commitTransaction();
	session.close();
	return arrayAmigo;
}

public Amigo retrieve(String pk) throws Exception {
	Session session = factory.openSession();
	session = HibernateUtil.getSession();
	//Session session = factory.openSession();
	Amigo amigo = (Amigo) session.load(Amigo.class, pk);
	session.flush();
	HibernateUtil.commitTransaction();
	session.close();
	return amigo;
}

public void delete(Amigo amigo) throws Exception {
	Session session = factory.openSession();
	session = HibernateUtil.getSession();
	//Session session = factory.openSession();
	session.delete(amigo);
	session.flush();
	HibernateUtil.commitTransaction();
	session.close();
}

try {
      ....
} catch (Exception e) {
      e.printStackTrace();
}

Session session = factory.openSession();
session = HibernateUtil.getSession();

Session session = factory.openSession();