org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: entities, no session or session was closed

@OneToMany(cascade=CascadeType.ALL, fetch=FetchType.LAZY, mappedBy="entity")
    public Set getCollection() {
        return this.collection;
    }

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class HibernateFactory {

    private static SessionFactory sessionFactory;
    private static Log log = LogFactory.getLog(HibernateFactory.class);

    /**
     * Constructs a new Singleton SessionFactory
     * @return
     * @throws HibernateException
     */
    public static SessionFactory buildSessionFactory() throws HibernateException {
        if (sessionFactory != null) {
            closeFactory();
        }
        return configureSessionFactory();
    }

    /**
     * Builds a SessionFactory, if it hasn't been already.
     */
    public static SessionFactory buildIfNeeded() throws DataAccessLayerException {
        if (sessionFactory != null) {
            return sessionFactory;
        }
        try {
            return configureSessionFactory();
        } catch (HibernateException e) {
            throw new DataAccessLayerException(e);
        }
    }

    public static SessionFactory getSessionFactory() {
        return sessionFactory;
    }

    public static Session openSession() throws HibernateException {
        buildIfNeeded();
        return sessionFactory.openSession();
    }

    public static void closeFactory() {
        if (sessionFactory != null) {
            try {
                sessionFactory.close();
            } catch (HibernateException ignored) {
                log.error("Couldn't close SessionFactory", ignored);
            }
        }
    }

    public static void close(Session session) {
        if (session != null) {
            try {
                session.close();
            } catch (HibernateException ignored) {
                log.error("Couldn't close Session", ignored);
            }
        }
    }

    public static void rollback(Transaction tx) {
        try {
            if (tx != null) {
                tx.rollback();
            }
        } catch (HibernateException ignored) {
            log.error("Couldn't rollback Transaction", ignored);
        }
    }

    /**
     *
     * @return
     * @throws HibernateException
     */
    private static SessionFactory configureSessionFactory() throws HibernateException {
        Configuration configuration = new Configuration();
        configuration.configure();
        sessionFactory = configuration.buildSessionFactory();
        return sessionFactory;
    }
}

import hibernate.util.HibernateFactory;
import java.util.List;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.Transaction;

public abstract class AbstractDao {

    private Session session;
    private Transaction tx;

    public AbstractDao() {
        HibernateFactory.buildIfNeeded();
    }

    protected void saveOrUpdate(Object obj) {
        try {
            startOperation();
            session.saveOrUpdate(obj);
            tx.commit();
        } catch (HibernateException e) {
            handleException(e);
        } finally {
            HibernateFactory.close(session);
        }
    }

    protected void delete(Object obj) {
        try {
            startOperation();
            session.delete(obj);
            tx.commit();
        } catch (HibernateException e) {
            handleException(e);
        } finally {
            HibernateFactory.close(session);
        }
    }

    protected Object find(Class clazz, Integer id) {
        Object obj = null;
        try {
            startOperation();
            obj = session.get(clazz, id);
            tx.commit();
        } catch (HibernateException e) {
            handleException(e);
        } finally {
            HibernateFactory.close(session);
        }
        return obj;
    }

    protected Object find(Class clazz, String id) {
        Object obj = null;
        try {
            startOperation();
            obj = session.get(clazz, id);
            tx.commit();
        } catch (HibernateException e) {
            handleException(e);
        } finally {
            HibernateFactory.close(session);
        }
        return obj;
    }

    protected List findAll(Class clazz) {
        List objects = null;
        try {
            startOperation();
            Query query = session.createQuery("from " + clazz.getName());
            objects = query.list();
            tx.commit();
        } catch (HibernateException e) {
            handleException(e);
        } finally {
            HibernateFactory.close(session);
        }
        return objects;
    }

    protected void handleException(HibernateException e) throws DataAccessLayerException {
        HibernateFactory.rollback(tx);
        throw new DataAccessLayerException(e);
    }

    protected void startOperation() throws HibernateException {
        session = HibernateFactory.openSession();
        tx = session.beginTransaction();
    }
}

<?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.MySQLDialect</property>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/databse</property>
    <property name="hibernate.connection.username">username</property>
    <property name="hibernate.connection.password">password</property>
  </session-factory>
</hibernate-configuration>