Locking of record using SQL in JAVA Websphere application.

Have Web app that reads record from iSeries to get a unique number, then
deletes that record.

Need to make sure that only one web user gets that unique number.

Application seems to work 99% of the time but sometimes log reports
duplicate key error message when using
unique number to write to transaction file. This seems to suggest that
more than one user retrieved the
unique number.

I use SQL to access the iSeries, setting the connection to
TRANSACTION_SERIALIZABLE to lock the record.

Appreciate any help on this issue.

Many thanks.

Below is the code :

sqlSelect="SELECT AMMBR# FROM MBPRDDTA.MBAMBRP WHERE AMGRWS= ? FOR
UPDATE";
try{
con=AS400ConnectionManager.getInstance().getConnection();
con.setTransactionIsolation
(Connection.TRANSACTION_SERIALIZABLE);
psmt=con.prepareStatement(sqlSelect);
psmt.setString(1,memberData.getTradeIndividual());
ResultSet rs=psmt.executeQuery();
rs=psmt.executeQuery();

if(rs.next()){
response.setMemberNumber(rs.getLong("AMMBR#"));
if (deleteMemberNumber(response.getMemberNumber
(),con)){
response.setStatus
(ApplicationStatus.SUCCESS);
response.setMessage("Successfully retrieved &
deleted member number from MBAMBRP");
}
}
con.commit();


}catch (SQLException e){
response.setMessage("SQL exception : Error retrieving &
deleting member number from MBAMBRP");
e.printStackTrace();
} catch (PersistenceException e) {
response.setMessage("Persistence exception : Error
retrieving & deleting member number from MBAMBRP");
e.printStackTrace();
}
finally{
try {
psmt.close();
con.close();
} catch (SQLException e) {
response.setMessage("SQL final exception : Error
retrieving & deleting member number from MBAMBRP");
e.printStackTrace();
}
}


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