Help with SQL class design

Question

Hello,
I was rocking along working on a CMS , when I found that my sql engine class
was not going to do what I needed. So I am now re-writng the class, This time I want
to make sure that my class will be able to handle any situation that my come up.
So, my question is, if I have a SQL result containg multiple data types would
using getObject be ok to use. In the code below I just want to return a vector
full of vectors containg objects. Then let who ever called this class parse the
returned vector and cast objects as needed.
I this a good design?
thanks,
jd
public Vector mkStmnt(String sqlCommand){
  sqlConnect();
  Vector resVector = new Vector();
  Vector resFullVector = new Vector();
  ResultSet res = null;
  try{
    Statement stmt = con.createStatement();
    boolean b = stmt.execute(sqlCommand);
    if(b){
      res = stmt.getResultSet();
      while(res.next()){
        for(int i = 1; i <= res.getMetaData().getColumnCount(); i++){     
        resVector.add(res.getString(i)); // want to change this to getObject
     }                                                   // so it can handle doubles and strings
                                                             // correctly
        resFullVector.add(new Vector(resVector));
     resVector.removeAllElements();
    else{
       int updateCount = stmt.getUpdateCount();
       resVector.add(new Integer(updateCount).toString());
       resFullVector.add(new Vector(resVector));
       resVector.removeAllElements();
  }catch(Exception e){
     System.out.println(e + " catch 1");
  if(res != null){
    try{
      res.close();
     }catch(Exception e){
     System.out.println(e + "catch 2 ");
   closeCon();
   return resFullVector;
}

Answer 1

Well, you can't handle all possible statements wich such a construct. in addition, this conversion from a ResultSet to a self made Vector of Vector table costs too much performance. The casting is also expensive and the client code have to do lots of them. Much faster would be to return a ResultSet object and the client can get the values with specifc getXXX() methods. For simple, few requests this might be okay. i suggest you offer multiple choices in your "sql engine" class, e.g.:
     * Execute a SELECT statement on this object's connection.
     * @param sql SQL query with SELECT statement.
     * @return Result of the query or null if failed.
     * @throws SQLExceptionon error.
    public ResultSet select(String sql) throws SQLException {
        return select(getMyConnection(), sql);
    }//select()
     * Execute a SELECT statement on a specific connection.
     * @param connection Connection to use.
     * @param sql SQL query with SELECT statement.
     * @return ResultSet Result of the query or null if failed.
     * @throws SQLException on error.
    public ResultSet select(Connection connection, String sql) throws SQLException {
        ResultSet result = null;
        if (connection != null && sql != null) {
            Statement stmt = createStatement(connection);
            logger.fine(sql);
            boolean isResultSet = stmt.execute(sql);
            if (isResultSet) {
                result = stmt.getResultSet();
            } else { //update count or no more results
                stmt.close();
        }//else: input unavailable
        return result;
    }//select()
     * Get result of a SELECT statement in a Vector of Vector data structure (to be independent from
    * JDBC API in client code).
     * @param sql Select query to perform.
     * @return Vector with first element being a Vector with the column titles
     * and the remaining elements being Vectors with row values.
     * @throws SQLException on error.
    public Vector selectValues(String sql) throws SQLException {
        Vector result = null;
        if (sql != null) {
            ResultSet rs = select(sql);
            if (rs != null) {
                int columnCount = 0;
                //get titles:
                Vector titles = new Vector();
                try {
                    ResultSetMetaData rsmd = rs.getMetaData();
                    columnCount = rsmd.getColumnCount();
                    for (int i = 1; i <= columnCount; i++) {
                        String columnName = rsmd.getColumnName(i);
                        titles.addElement(columnName);
                    }//next column
                    result = new Vector();
                    result.addElement(titles);
                    //get values:
                    Vector row = null;
                    while (rs.next()) { //next row
                        row = new Vector(columnCount);
                        for (int i = 1; i <= columnCount; i++) { //for all columns
                            row.addElement(rs.getObject(i));
                        }//next column
                        result.addElement(row);
                    }//while(rs.next())
                } finally {
                    closeResultSet(rs);
            }//else: ResultSet is null
        }//else: input unavailable
        return result;
    }//selectValues()btw: resFullVector.add(new Vector(resVector)); is one Vector too much ;-)