DAO<T> (Dao genérico)

DAO.java

import java.io.Serializable;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.criteria.CriteriaQuery;

/**
 * DAO genérico.
 *
 * @author Dilnei Cunha
 */
public class DAO<T> implements Serializable {

    private final Class<T> classe;
    private EntityManager entityManager;

    public DAO(Class<T> classe, EntityManager entityManager) {
        this.classe = classe;
        this.entityManager = entityManager;
    }

    public void adiciona(T t) {
        entityManager.persist(t);
    }

    public void remove(T t) {
        entityManager.remove(entityManager.merge(t));
    }

    public void atualiza(T t) {
        entityManager.merge(t);
    }

    public List<T> listaTodos() {
        CriteriaQuery<T> query = entityManager.getCriteriaBuilder().createQuery(classe);
        query.select(query.from(classe));
        List<T> lista = entityManager.createQuery(query).getResultList();
        return lista;
    }

    public T buscaPorId(Long id) {
        return entityManager.find(classe, id);
    }
}