public class SubjectFile {
   private Long id;
   private Blob data;
   private String filename;
   //omit getter and setter
}

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd" >
<hibernate-mapping package="antar.acquisition.file" >
   <class name="SubjectFile" table="subject_file" lazy="true" >      
      <id name="id" column="id">
         <generator class="sequence">
            <param name="sequence">seq_subject_file</param>
         </generator>
      </id>      
      <property name="data" not-null="true" /> <!-- blob-->
      <property name="filename" length="255" not-null="true" unique="true"/>      
   </class>
</hibernate-mapping>

//Read and update in transaction
Transaction transaction = session.beginTransaction();
SubjectFile loadFile = (SubjectFile) session.get(SubjectFile.class, new Long(12));
byte[] readBytes = IOUtils.toByteArray(loadFile.getData().getBinaryStream());
assertEquals(1000, readBytes.length);  // data is 1000 bytes.
loadFile.setFilename("makeSomeChange.txt");

// fileName got updated but blob is truncated to 0 byte at database!
session.saveOrUpdate(reload); 
transaction.commit();
session.close();