Erro!

package teste;


public class Principal {
	/**
	* @param args
	*/
	public static void main(String[] args) {
	Cliente c1 = new Cliente();
	c1.setNome("Joaquim");
	c1.setIdade(new Long(12));
	Cliente c2 = new Cliente();
	c2.setNome("Renata");
	c2.setIdade(new Long(13));
	ClienteDAO clienteDAO = new ClienteDAO();
	clienteDAO.salvar(c1);
	clienteDAO.salvar(c2);
	
	}

	}

package teste;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;

	public class HibernateUtil {
		private static final SessionFactory sessionFactory;
		static {
			try {
// Create the SessionFactory from hibernate.cfg.xml
				sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
			} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
				System.err.println("Initial SessionFactory creation failed." + ex);
				throw new ExceptionInInitializerError(ex);
			}
		}
		public static SessionFactory getSessionFactory() {
			return sessionFactory;
		}
	}

package teste;
import java.io.Serializable;
import javax.persistence.*;

@Entity
@Table(name = "cliente")
public class Cliente implements Serializable {
	@Id @GeneratedValue(strategy = GenerationType.AUTO)
	private Long id;
	@Column(name = "nome_cliente", nullable = false, length=60)
	private String nome;
	@Column(name = "idade_cliente", nullable = false, length = 5)
	private Long idade;
	
	
	public Cliente(){
	}
	public Long getId() {
		return id;
	}
	private void setId(Long id) {
		this.id = id;
	}
	public Long getIdade() {
		return idade;
	}
	public void setIdade(Long idade) {
		this.idade = idade;
	}
	public String getNome() {
	return nome;
	}
	public void setNome(String nome) {
		this.nome = nome;
}
}

package teste;
import org.hibernate.Session;
import org.hibernate.mapping.List;

import teste.Cliente;
import teste.HibernateUtil;

public class ClienteDAO {
	private Session session;
	public ClienteDAO(){
}
	public void salvar(Cliente cli){
		session = HibernateUtil.getSessionFactory().getCurrentSession();
		session.beginTransaction();
		session.save(cli);
		session.getTransaction().commit();
}
	public List listar(){
		session = HibernateUtil.getSessionFactory().openSession();
		session.beginTransaction();
		List l1 = (List) session.createQuery("from Cliente").list();
		session.getTransaction().commit();
		return l1;
		}
}

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<!-- Database connection settings -->
<property name="connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="connection.url">jdbc:mysql://localhost/teste</property>
<property name="connection.username">root</property>
<property name="connection.password">123456</property>
<!-- JDBC connection pool (use the built-in) -->
<property name="connection.pool_size">1</property>
<!-- SQL dialect -->
<property name="dialect">org.hibernate.dialect.HSQLDialect</property>
<!-- Enable Hibernate's automatic session context management -->
<property name="current_session_context_class">thread</property>
<!-- Disable the second-level cache -->
<property name="cache.provider_class">org.hibernate.cache.NoCacheProvider</property>
<!-- Echo all executed SQL to stdout -->
<property name="show_sql">true</property>
<mapping class="teste.Cliente"/>
</session-factory>
</hibernate-configuration>