Problema com Hibernate

<?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>
    <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
    <property name="hibernate.connection.url">jdbc:postgresql://localhost:5432/Hibernate</property>
    <property name="hibernate.connection.username">postgres</property>
    <property name="hibernate.connection.password">12345</property> 
    <property name="hibernate.show_sql">true</property>
    <property name="hibernate.current_session_context_class">thread</property> 
  </session-factory>
</hibernate-configuration>

hibernate.dialect org.postgresql.Driver
hibernate.connection.url jdbc:postgresql://localhost:5432/postgres
hibernate.connection.username postgres
hibernate.connection.password 12345

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n


log4j.rootLogger=info, stdout

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate Mapping DTD 3.0//EN" 
"hibernate-mapping-3.0.dtd">

<hibernate-mapping>
   <class name="Usuario" table="db_usuarios">
       <id name="UsCod"  column="USCOD"  type="string">
            < generator class="assigned"/>
        </id>
        <property name="UsSenha" column="USSENHA" type="string"/>
        <property name="UsNome" column="USNOME" type="string"/>
        <property name="UsEmail" column="USEMAIL" type="string"/>
    </class>
</hibernate-mapping>


log4j.logger.org.hibernate.test=info

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="org.somepackage.eg">
  	

<class name="Foo" table=?FooTable?>
  	  	

<id name="id" type=?java.lang.Long?>
  	  	  	<generator class=?sequence?/>
  	  	</id>
  	</class>
</hibernate-mapping>

public class Teste {

public static void main(String[] args) throws Exception {
    
	try
	{
		String log = "login";
		String senha = "abc";
		String nome = "Rafael";
		String email = "[email removido]";

		UsuarioDAO dao = new UsuarioDAO();
		Usuario usuario = new Usuario(log,senha,nome,email);
		dao.UsInserir(usuario);
		System.out.println("Registro inserido com sucesso!!!");
		}
		catch(Exception e)
		{
			System.out.println("Não foi possivel, Erro: " + e.getMessage());
		}
	}
}

public class Usuario {
	private String usCod;
	private String usSenha;
	private String usNome;
	private String usEmail;

	public Usuario(){
	}

	public Usuario(String usCod, String usSenha, String usNome, String usEmail) {
		this.setUsCod(usCod);
		this.setUsSenha(usSenha);
		this.setUsNome(usNome);
		this.setUsEmail(usEmail);
	}

    public String getUsCod() {
        return usCod;
    }

    public void setUsCod(String usCod) {
        this.usCod = usCod;
    }

    public String getUsEmail() {
        return usEmail;
    }

    public void setUsEmail(String usEmail) {
        this.usEmail = usEmail;
    }

    public String getUsNome() {
        return usNome;
    }

    public void setUsNome(String usNome) {
        this.usNome = usNome;
    }

    public String getUsSenha() {
        return usSenha;
    }

    public void setUsSenha(String usSenha) {
        this.usSenha = usSenha;
    }

    
            }

import java.util.List;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;
import org.hibernate.criterion.Expression;

public class UsuarioDAO{

	private SessionFactory factory;

	public UsuarioDAO() throws Exception{
		factory = new Configuration().addClass(Usuario.class).buildSessionFactory();

	}

	public void UsInserir(Usuario us) throws Exception {
		Session session = factory.openSession();
		session.save(us);
		session.flush();
		session.close();
	}

	public void UsAlterar(Usuario us) throws Exception {
		Session session = factory.openSession();
		session.update(us);
		session.flush();
		session.close();
	}
	public void UsExcluir(Usuario us) throws Exception {
		Session session = factory.openSession();
		session.delete(us);
		session.flush();
		session.close();
	}
}