Not binding factory to JNDI, no JNDI name configured
org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.hibernate.model.Story#0]
        at org.hibernate.engine.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:590)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performUpdate(DefaultSaveOrUpdateEventListener.java:284)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsDetached(DefaultSaveOrUpdateEventListener.java:223)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:89)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
        at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:507)
        at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:499)
        at org.hibernate.engine.CascadingAction$5.cascade(CascadingAction.java:218)
        at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:268)
        at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:216)
        at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
        at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:296)
        at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:242)
        at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:219)
        at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
        at org.hibernate.engine.Cascade.cascade(Cascade.java:130)
        at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:456)
        at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:334)
        at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:181)
        at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
        at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
        at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
        at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
        at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
        at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)

package com.hibernate.model;

import java.util.List;

public class Group
{
    private int id;
    private String name;
    private List stories;

    public Group()
    {

    }

    public Group(String name)
    {
        this.name = name;       
    }

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }

    public List getStories()
    {
        return stories;
    }

    public void setStories(List stories) {
        this.stories = stories;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Group other = (Group) obj;
        if (this.id != other.id) {
            return false;
        }
        if ((this.name == null) ? (other.name != null) : !this.name.equals(other.name)) {
            return false;
        }
        if (this.stories != other.stories && (this.stories == null || !this.stories.equals(other.stories))) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 59 * hash + this.id;
        hash = 59 * hash + (this.name != null ? this.name.hashCode() : 0);
        hash = 59 * hash + (this.stories != null ? this.stories.hashCode() : 0);
        return hash;
    }
}

package com.hibernate.model;

public class Story
{
    private int id;
    private String info;   

    public Story()
    {

    }

    public Story(String info)
    {
        this.info = info;
    }

    public int getId()
    {
        return id;
    }

    public void setId(int id)
    {
        this.id = id;
    }

    public String getInfo()
    {
        return info;
    }

    public void setInfo(String info)
    {
        this.info = info;
    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Story other = (Story) obj;
        if (this.id != other.id) {
            return false;
        }
        if ((this.info == null) ? (other.info != null) : !this.info.equals(other.info)) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 97 * hash + this.id;
        hash = 97 * hash + (this.info != null ? this.info.hashCode() : 0);
        return hash;
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.hibernate.model.Group" table="grouptable">
        <id name="id" type="integer" unsaved-value="null" column="id">
            <generator class="increment" />
        </id>
        <list name="stories" cascade="save-update">
            <key column="parent_id" />
            <index column="idx" />
            <one-to-many class="com.hibernate.model.Story" />
        </list>
        <property name="name" type="string" column="name"/>
    </class>
</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.hibernate.model.Story" table="story">
        <id name="id" type="integer" unsaved-value="null" column="id">
            <generator class="increment" />
        </id>
        <property name="info" type="string" column="info"/>
    </class>
</hibernate-mapping>

package com.hibernate.session;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.SessionFactory;

public class HibernateUtil
{
    private static SessionFactory sessionFactory;
    private static final ThreadLocal<Session> threadLocal = new ThreadLocal<Session>();

    static
    {
        try
        {
            sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
        }
        catch (Throwable ex)
        {
            System.err.println("Initial SessionFactory creation failed." + ex);
            throw new ExceptionInInitializerError(ex);
        }
    }

    public static Session getSession() throws HibernateException
    {
        Session session = (Session) threadLocal.get();

      if (session == null || !session.isOpen())
      {
         if (sessionFactory == null)
         {
            rebuildSessionFactory();
         }
         session = (sessionFactory != null) ? sessionFactory.openSession(): null;
         threadLocal.set(session);
      }

        return session;
    }

    public static void rebuildSessionFactory()
    {
      try
      {
         sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory();
      }
      catch (Exception e)
      {
         System.err.println("%%%% Error Creating SessionFactory %%%%");
         e.printStackTrace();
      }
   }

    public static void closeSession() throws HibernateException
    {
        Session session = (Session) threadLocal.get();
        threadLocal.set(null);

        if (session != null)
        {
            session.close();
        }
    }

   public static org.hibernate.SessionFactory getSessionFactory()
   {
      return sessionFactory;
   }
}

<?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://127.0.0.1:3306/learning_java</property>
    <property name="hibernate.connection.username">root</property>
    <mapping resource="com/hibernate/model/Group.hbm.xml"/>
    <mapping resource="com/hibernate/model/Story.hbm.xml"/>
  </session-factory>
</hibernate-configuration>