<hibernate-mapping>
    <class name="eg.Bean" table="BEANS">
        <id name="id" column="BEANID" type="integer">
            <generator class="native"/>
        </id>
      <dynamic-component name="properties">
         <property name="test01" column="TEST01" type="string" length="64"/>
      </dynamic-component>
    </class>
</hibernate-mapping>

public class Bean {
   private Integer id;
   private Map properties = new HashMap();
   
   public Integer getId() { return id; }
   public void setId(Integer id) { this.id = id; }
   
   public Map getProperties() { return properties; }
   public void setProperties(Map properties) {
      if (properties == null)
         throw new IllegalArgumentException("Why should I be nulled?");
      this.properties = properties;
   }
}

public class Test {
   public static void main(String[] args) {
      Configuration cfg = new Configuration().configure();
      new SchemaExport(cfg).create(false, true);
      SessionFactory sf = cfg.buildSessionFactory();
      Session s = sf.openSession();
      
      s = sf.openSession();
      Bean b = new Bean();
      s.save(b);
      s.flush();
      s.close();
      Integer id = b.getId();
      
      s = sf.openSession();
      b = (Bean) s.get(Bean.class, id); //This will set properties to null
   }
}