invalid large object descriptor : 0 hibernate and postgres - postgresql

Question

We have a n tier application where we are reading the BLOB objects stored in the postgres database.
At times when we are trying to access the blob object through input stream we get "org.postgresql.util.PSQLException: ERROR: invalid large-object descriptor: 0" after reading the other blogs, this exception comes whenever we are trying to access the BLOB outside the transaction (transaction is committed).
But, in our case we get this exception even though the transaction is active. The BLOB is read within the transaction.
Any pointers as to why this exception is occuring even though the transaction is active?

Answer 1

Your description of the problem does not have specifics but in my code this error showed up when I tried to use Large Object outside the data access method. As in your case, the object was formed in the method. This is consistent with what other people noticed in this forum: Large Object exists only within the data access method (or transaction). I needed byte[] so I converted Large Object within the method, wrapped it up in a Data Transfer Object and was able to use it in other layers. This are relevant code snippets:
//This is Data Access Class
#Named
public class SupportDocsDAO {
protected ResultSet resultSet;
private LargeObject lob;
// SupportDocs is an Entity class in Data Transfer Objects package
private SupportDocs supportDocsDTO;
public LargeObject getLob() {
return lob;
}
public void setLob(LargeObject lob) {
this.lob = lob;
}
public SupportDocs getSupportDocsDTO() {
return supportDocsDTO;
}
public void setSupportDocsDTO(SupportDocs supportDocsDTO) {
this.supportDocsDTO = supportDocsDTO;
}
//.... other code
public SupportDocs fetchSupportDocForDescr(SupportDocs supportDocs1) {
Session session = HibernateUtil.getSessionFactory().openSession();
session.doWork(new Work() {
#Override
public void execute(java.sql.Connection connection) throws SQLException {
java.sql.PreparedStatement ps = null;
try {
LargeObjectManager lobm =
connection.unwrap(org.postgresql.PGConnection.class).getLargeObjectAPI();
ps = connection.prepareCall("{call ret_lo_supportdocs_id(?)}");
ps.setInt(1, supportDocs1.getSuppDocId());
ps.execute();
resultSet = ps.getResultSet();
while (resultSet.next()) {
supportDocsDTO.setFileNameDoc(resultSet.getString("filenamedoc"));
supportDocsDTO.setExtensionSd(resultSet.getString("extensionsd"));
long oid = resultSet.getLong("suppdoc_oid");
setLob(lobm.open(oid, LargeObjectManager.READ));
//This is the conversion of Large Object into byte[]
supportDocsDTO.setSuppDocImage(lob.read(lob.size()));
System.out.println("object size: " + lob.size());
}
// other code, catch, cleanup with finally, and return supportDocsDTO
This works without problems. I can recreate images and videos from obtained byte[].