When overwritting CLOB longer previous value still remains

Question

Hi,
I have a problem with updating CLOB's. Below is how I write them:
String selectStatement = "select description from modules where " +
"system = ? and version = ? and module = ? for update";
PreparedStatement selStmt = con.prepareStatement(selectStatement);
selStmt.setString(1, system);
selStmt.setString(2, version);
selStmt.setString(3, module);
ResultSet rset = selStmt.executeQuery();
ResultSetInPool rpool = (ResultSetInPool)rset;
if (rpool.next()) {
desclob = (CLOB)((OracleResultSet)rpool.getUnderlyingResultSet()).getCLOB(1);
// Write character stream (description) to CLOB variable
writer = ((CLOB)desclob).getCharacterOutputStream();
writer.write(description.toCharArray());
writer.flush();
} else {
throw new NoSuchEntityException("Row does not exist");
The problem is that when there is a value already written which is longer then new one, part of the old value (which has not been overwriten) still remains in the database. Is that normal behavior? Is there any way how to address this problem better/faster then updating row with EMPTY_CLOB() and writting string again?
Thanks for response in advance,
RAF

Answer 1

Hi Rafal,
If you are using Oracle9i JDBC Drivers, then use the
oracle.sql.CLOB.trim(long offset) method to clear the contents of the CLOB.
like ,
// clear the contents of clob
clob.trim(0);
else If you are using JDK 1.4 , use java.sql.Clob.truncate(long offset)
clob.truncate(0);
then start streaming the new contents into the clob.
I guess its the normal behaviour of CLOB.
Regards
Elango.