public class AlunosApplication extends Application implements SessionManager {
    @Override
    public void init() {
        getContext().addTransactionListener(new TransactionListener() {
            @Override
            public void transactionEnd(Application application, Object transactionData) {
                if (application == BiometriaApplication.this) {
                    closeSession();
                }
            }
 
            @Override
            public void transactionStart(Application application, Object transactionData) {
 
            }
        });
    }

    /**
     * Retorna a sessão atual do Hibernate. 
     * Também assegura uma transação aberta do Hibernate.
     */
    public Session getSession() {
        Session currentSession = HibernateUtil.getSessionFactory().getCurrentSession();
        if(!currentSession.getTransaction().isActive()) {
            currentSession.beginTransaction();
        }
        return currentSession;
    }
 
    private void closeSession() {
        Session sess = HibernateUtil.getSessionFactory().getCurrentSession();
        if(sess.getTransaction().isActive()) {
            sess.getTransaction().commit();
        }
        if (sess.isOpen()) sess.close();
    }

package net.rubensgadelha.alunos.util;
 
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
 
public class HibernateUtil {
    private static final SessionFactory sessionFactory;
 
    static {
        try {
            // Cria o SessionFactory com base no arquivo hibernate.cfg.xml
            sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
	} catch (Throwable ex) {
            System.err.println("Falha na inicialização da SessionFactory: " + ex);
            throw new ExceptionInInitializerError(ex);
	}
    }
 
    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }
}

package net.rubensgadelha.alunos.bean;
 
import java.io.Serializable;
 
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
 
import org.hibernate.validator.Length;
import org.hibernate.validator.NotNull;
 
@SuppressWarnings("serial")
@Entity
@Table(name="alunos")
public class Aluno implements Serializable {
 
    @Id
    private Long oid;
 
    @Column(name="matricula", nullable=false, length=5)
    @NotNull
    private Integer matricula;
 
    @Column(name="nome")
    @NotNull @Length(min=5, max=50)
    private String nome;
 
    @Column(name="email")
    private String email;
 
    public void setOid(Long oid) {
        this.oid = oid;
    }
 
    public Long getOid() {
        return oid;
    }
 
    public void setMatricula(Integer matricula) {
        this.matricula = matricula;
    }
 
    public Integer getMatricula() {
        return matricula;
    }
 
    public String getNome() {
        return nome;
    }
 
    public void setNome(String nome) {
        this.nome = nome;
    }
 
    public String getEmail() {
        return email;
    }
 
    public void setEmail(String email) {
        this.email = email;
    }
}

package net.rubensgadelha.alunos.ui;
 
import net.rubensgadelha.alunos.AlunosApplication;
import net.rubensgadelha.alunos.bean.Aluno;
import net.rubensgadelha.alunos.util.HbnContainer;
 
import com.vaadin.ui.Table;
 
@SuppressWarnings("serial")
public class TabelaAlunos extends Table {
 
    public ListaAlunos(AlunosApplication app) {
        HbnContainer hbn = new HbnContainer(Aluno.class, app);
        setContainerDataSource(hbn);
    }
}