Error org.hibernate.Lazyinitializationexception how to resolve?

Question

I know this error is derived from trying to fetch some data from the database when I have no session open.

But the biggest problem for me is that this error is appearing to me completely random, as I am developing a server that processes data and then sends to clients, every 3 minutes the server repeats the same operations, but the error either appears right on the server run or may appear after 3 or 4 hours of running the server.

The error always points to the class Produto more precisely for the method toString, I commented the method and now gives error in hashCode.

Structure in the database:

|| Lot || ----Contains ---> || Product || ----Contains ---> || qualityGates ||

Code -> Product.java

public class Produto  implements java.io.Serializable {


     private Integer idProduto;
     private Qualitygate qualitygateByIdQualityGate3;
     private Qualitygate qualitygateByIdQualityGate2;
     private Qualitygate qualitygateByIdQualityGate1;
     private Familiaproduto familiaproduto;
     private String noproduto;
     private Integer vt;
     private String tipo;
     private Set loteestados = new HashSet(0);

    public Produto() {
    }

//++ GET'S & SET'S

    @Override
    public int hashCode() {
        int hash = 5;
        hash = 59 * hash + Objects.hashCode(this.idProduto);
        hash = 59 * hash + Objects.hashCode(this.qualitygateByIdQualityGate3); // <-----erro
        hash = 59 * hash + Objects.hashCode(this.qualitygateByIdQualityGate2);
        hash = 59 * hash + Objects.hashCode(this.qualitygateByIdQualityGate1);
        hash = 59 * hash + Objects.hashCode(this.familiaproduto);
        hash = 59 * hash + Objects.hashCode(this.noproduto);
        hash = 59 * hash + Objects.hashCode(this.vt);
        hash = 59 * hash + Objects.hashCode(this.tipo);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Produto other = (Produto) obj;
        if (!Objects.equals(this.idProduto, other.idProduto)) {
            return false;
        }
        if (!Objects.equals(this.qualitygateByIdQualityGate3, other.qualitygateByIdQualityGate3)) {
            return false;
        }
        if (!Objects.equals(this.qualitygateByIdQualityGate2, other.qualitygateByIdQualityGate2)) {
            return false;
        }
        if (!Objects.equals(this.qualitygateByIdQualityGate1, other.qualitygateByIdQualityGate1)) {
            return false;
        }
        if (!Objects.equals(this.familiaproduto, other.familiaproduto)) {
            return false;
        }
        if (!Objects.equals(this.noproduto, other.noproduto)) {
            return false;
        }
        if (!Objects.equals(this.vt, other.vt)) {
            return false;
        }
        if (!Objects.equals(this.tipo, other.tipo)) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return " noproduto=" + noproduto;
    }
//    @Override
//    public String toString() {
//        return "Produto{" + "idProduto=" + idProduto + ", qualitygateByIdQualityGate3=" + qualitygateByIdQualityGate3 + ", qualitygateByIdQualityGate2=" + qualitygateByIdQualityGate2 + ", qualitygateByIdQualityGate1=" + qualitygateByIdQualityGate1 + ", familiaproduto=" + familiaproduto + ", noproduto=" + noproduto + ", vt=" + vt + ", tipo=" + tipo + ", loteestados=" + loteestados + '}';
//    }

  }

Code -> Product.hbm.xml

<hibernate-mapping>
  <class catalog="mydb" name="Models.Produto" table="produto">
    <id name="idProduto" type="java.lang.Integer">
      <column name="idProduto"/>
      <generator class="identity"/>
    </id>
    <many-to-one class="Models.Qualitygate" fetch="select" name="qualitygateByIdQualityGate3">
      <column name="idQualityGate3"/>
    </many-to-one>
    <many-to-one class="Models.Qualitygate" fetch="select" name="qualitygateByIdQualityGate2">
      <column name="idQualityGate2"/>
    </many-to-one>
    <many-to-one class="Models.Qualitygate" fetch="select" name="qualitygateByIdQualityGate1">
      <column name="idQualityGate1"/>
    </many-to-one>
    <many-to-one class="Models.Familiaproduto" fetch="select" name="familiaproduto">
      <column name="idNomeProduto"/>
    </many-to-one>
    <property name="noproduto" type="string">
      <column length="45" name="noproduto" not-null="true" unique="true"/>
    </property>
    <property name="vt" type="java.lang.Integer">
      <column name="vt"/>
    </property>
    <property name="tipo" type="string">
      <column length="10" name="tipo"/>
    </property>
    <set fetch="select" inverse="true" lazy="true" name="loteestados" table="loteestado">
      <key>
        <column name="ProdutoidProduto" not-null="true"/>
      </key>
      <one-to-many class="Models.Loteestado"/>
    </set>
  </class>
</hibernate-mapping>

Code -> Genericodao Session creation (At first there was the HibernateUtil to create me the sessions but due to the problem of creating many sessions and giving full memory error I changed to this approach)

public class GenericDao<T extends Serializable> {

    private static Session session;
    public Class<T> persistentClass;

    public GenericDao(){
        //this.session = HibernateUtil.getSession();
        this.persistentClass = (Class<T>) ((ParameterizedType) 
            getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }

    public Session createSession(){
            Configuration cfg= new Configuration().configure();
        SessionFactory sessionfactory=cfg.buildSessionFactory();
        session=sessionfactory.openSession();

        return this.session;
    }
    public Session getSession() {
        if(this.session == null || !this.session.isOpen()){  
           return createSession();
        } else return session;
    }

    protected void save(T entity) {

         try {

            Session session = getSession();
            session.beginTransaction();
            session.save(entity);
            session.getTransaction().commit();
        } catch (Exception e) {
            session.getTransaction().rollback();

        } finally {
            session.close();
        }

   }

// ----------------------- +outros métodos 

    public T findById(Integer id) {
        return (T) getSession().createCriteria(persistentClass)
                .add(Restrictions.eq("id", id)).uniqueResult();
    }


    private void close() {
        if (getSession() != null && getSession().isOpen()) {
            getSession().close();
        }
    }
}

Any solution to this problem?

Answer 1

First of all, if you always use accesses all object attributes, you should use the mode ager and not Lazy.

However, the problem may have its cause in the fact that, in certain circumstances, Hibernate creates proxies in entities Lazy, which means it doesn’t load the data until it intercepts a call to a method getter.

I myself have had problems accessing attributes in these types of objects. Solution? Try call the method getter instead of accessing the attributes directly.

For example, where do you do this:

hash = 59 * hash + Objects.hashCode(this.idProduto);

You can switch to that:

hash = 59 * hash + Objects.hashCode(this.getIdProduto());