How can I make a generic version of this function

Question

Hi,
I have a lot of functions that follow the same general format:
public static List<ProductRecord> listProducts(int category, Connection con)
throws SQLException
     // prepare a statement
     PreparedStatement stmt = con.prepareStatement(SQL_LIST /* sql to list product records */);
     try
          // set some parameters
          stmt.setInt(1, category);
          // execute the query
          ResultSet rs = stmt.executeQuery();
          // create a vector for storing the result
          Vector<ProductRecord> list = new Vector<ProductRecord>();
          // append all records to the list
          while (rs.next()) {
               list.add(new ProductRecord(rs));
          // return the list
          return list;
     finally
          stmt.close();
}Is there a way I can streamline this using generic functions?
It would be great if I could write a generic function that could simplify each function to something like:
public static List<ProductRecord> listProducts(int category, Connection con)
throws SQLException
     return someSpecialFunction<ProductRecord>(SQL_LIST, con, category /* would use a argument list here... */);
public static <T extends DatabaseRecord> T someSpecialFunction(String sql, Connection con, Object ... params)
     // prepare a statement
     PreparedStatement stmt = con.prepareStatement(sql);
     try
          // set some parameters
          for (int i = 0; i < params.length; i++) {
               stmt.setObject(i+1, params);
          // execute the query
          ResultSet rs = stmt.executeQuery();
          // create a vector for storing the result
          Vector<T> list = new Vector<T>();
          // append all records to the list
          while (rs.next()) {
               list.add(new T(rs)); /* dont know how I could achieve this */
          // return the list
          return list;
     finally
          stmt.close();
I dont seem to understand generics engough to be able to complete the function.
Any ideas or suggestions on how I could achieve this would be greatly appreciated.
Thanks in advance!
- Robert

Answer 1

You'll need to pass T.class as well, because you can't do "new T(rs)" but you can do "Tclass.asSubclass(Tclass).getConstructor(ResultSet.class).newInstance (rs)" (I've not tested my code)
public static <T extends DatabaseRecord> T someSpecialFunction(String sql, Connection con, Class<? extends T> Tclass, Object ... params) {
      list.add (Tclass.asSubclass (Tclass). getConstructor(ResultSet.class).newInstance (rs));
}