Erro getId

Front-end
#1

Olá pessoal estou tentando implementar o id como autoincremento na minha classe usuario só que está dando o seguinte erro:

Mapping:

<hibernate-mapping>
    <class name="entidades.Usuario" table="usuario">
        <id name="id" column="id">        
            <generator class="increment"/>
        </id>
       
        <property name="nome" column="nome"/>
        <property name="sexo" column="sexo"/>
        <property name="dataNasc" column="dataNasc"/>
        <property name="setor" column="setor"/>
        <property name="login" column="login"/>
        <property name="senha" column="senha"/>
           
    </class>
</hibernate-mapping>

Classe para testar a inclusão:

[code]
public class Teste {
private UsuarioDAO uDAO = DAOFactory.getInstance().getUsuarioDAO();

public Teste(){
    testar();
}

public void testar(){
    
    Usuario u1 = new Usuario();
    
    u1.setNome("João");
    u1.setSexo("f");
    u1.setDataNasc("05/10/1985");
    u1.setSetor("cap");
    u1.setLogin("joao");
    u1.setSenha("123456");
    
    try{
        
        SessionFactory session = null;
        
        session = new Configuration()
            .configure("hibernate.cfg.xml" )
            .buildSessionFactory();             
      
        
        uDAO.save( u1 );
        System.out.println("Nome: " + u1.getId());
        session.close(); 

}catch(HibernateException e1){
    e1.printStackTrace();
}

}

public static void main(String[] args){
    Teste teste = new Teste();        
    
}

}[/code]

Erro:

Compiling 1 source file to D:\Estudos_Java\TCC\build\classes
compile-single:
run-single:
log4j:WARN No appenders could be found for logger (org.hibernate.cfg.Environment).
log4j:WARN Please initialize the log4j system properly.
org.hibernate.PropertyAccessException: Exception occurred inside getter of entidades.Usuario.id
        at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:148)
        at org.hibernate.engine.UnsavedValueFactory.getUnsavedIdentifierValue(UnsavedValueFactory.java:44)
        at org.hibernate.tuple.PropertyFactory.buildIdentifierProperty(PropertyFactory.java:44)
        at org.hibernate.tuple.EntityMetamodel.<init>(EntityMetamodel.java:115)
        at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:411)
        at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:108)
        at org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:55)
        at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:215)
        at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1152)
        at teste.Teste.testar(Teste.java:45)
        at teste.Teste.<init>(Teste.java:27)
        at teste.Teste.main(Teste.java:60)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at org.hibernate.property.BasicPropertyAccessor$BasicGetter.get(BasicPropertyAccessor.java:145)
        ... 11 more
Caused by: java.lang.NullPointerException
        at entidades.Usuario.getId(Usuario.java:40)
        ... 16 more
BUILD SUCCESSFUL (total time: 2 seconds)
#2