Java Database Connectivity (JDBC)

I'm using JDBC and the Oracle JDBC driver to call a PL/SQL function that returns a SYS_REFCURSOR. I do this via a CallableStatement object and then cast the output parameter to a ResultSet object. However, I want this ResultSet object I end up with to be updateable. The following code throws an exception stating "Invalid operation for read only resultset: updateString ":

       
cstmt2 = con.prepareCall("{? = call get_upload_entry_for_update(?)}",
                         ResultSet.TYPE_FORWARD_ONLY,
                         ResultSet.CONCUR_UPDATABLE);
cstmt2.registerOutParameter(1, OracleTypes.CURSOR);
cstmt2.setInt(2, newUploadId);
cstmt2.execute();
rs = (ResultSet) cstmt2.getObject(1);
rs.next();
rs.updateString("UPLOAD_FILENAME", fileName);
// . . .

So even though, I create the CallableStatement such that ResultSets should be updateable, it's not allowing me to do any updates. Also, in case you're wondering, inside the PL/SQL function, the query on which the cursor is based is a select statement which does specify "for update" at the end.

I can get it to work as follows using a Statement object that executes the SELECT statement directly instead of a CallableStatement that executes a PL/SQL function:

       

Statement stmt = con.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE);
rs = stmt.executeQuery("select UPLOAD_FILENAME, UPLOAD_FILE from rf_upload where upload_id = "+newUploadId+" for update");

rs.next();
rs.updateString("UPLOAD_FILENAME", fileName);
//. . . 

Although this works, the project I'm working has a goal to encapsulate all SQL into Functions and Stored Procedures so I'd like to get it working that way instead.

So the bottom-line question is: Using the Oracle JDBC driver, how can I call a PL/SQL function in such a way that I can obtain an updateable ResultSet object?

Thanks for any suggestions. I'd be happy to clarify anything that's unclear.