General error when accessing blob from oracle

Question

Hi
I have successfully uploaded and saved images into oracle(8.1.5) table DATA_TYPE(dtid number, iconname varchar2(30), icon blob). When I try to retrieve icon from the database, I get "javax.servlet.ServletException: General error" at:
PreparedStatement pstmt = myConnection.prepareStatement(mySQL);
My code looks like this:
imgModifyDataType.jsp
<%
ResultSet myResultSet = null;
Statement myStatement = null;
Connection myConnection = null;
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver").newInstance();
myConnection = DriverManager.getConnection("Jdbc:Odbc:Te","te","te");
String iconName;
String pDTID = request.getParameter("dtid");
String mySQL = "Select iconname, icon from data_types where dtid=?";
//Following statement throws general error exception
PreparedStatement pstmt = myConnection.prepareStatement(mySQL);
pstmt.setString(1,pDTID);
myResultSet = pstmt.executeQuery();
iconName = myResultSet.getString("iconname");
myUpload.initialize(pageContext);
myUpload.downloadField(myResultSet,"icon","application/x-msdownload", iconName);
%>
One more thing. The error occurs only when I try to execute query retrieving blob data. The same set of statements works fine for simple text or numbers.
Please help

Answer 1

When you read a BLOB with ORACLE,
you have to lock the corresponding row.
This means that...
- the connection must not be in "AUTO COMMIT" mode
- you have to do a "SELECT ... FOR UPDATE"