I am making a number of distinct controllers, one relating to each stored procedure in a database. These are only used to read data and making them available in JSON format for javascripts.

My code so far looks like this, and I'm wondering if I have missed any opportunities to re-use code, maybe make some help classes. I have way too little experience doing OOP, so any help and suggestions here would be really appreciated.

Here is my generalized code so far (tested and works);

using System;
using System.Configuration;
using System.Web.Mvc;
using System.Data;
using System.Text;
using System.Data.SqlClient;
using Prototype.Models;

namespace Prototype.Controllers
{
    public class NameOfStoredProcedureController : Controller
    {

        char[] lastComma = { ',' };

        String oldChar = "\"";
        String newChar = """;

        StringBuilder json = new StringBuilder();

        private String strCon = ConfigurationManager.ConnectionStrings["SomeConnectionString"].ConnectionString;
        private SqlConnection con;

        public StoredProcedureController()
        {
            con = new SqlConnection(strCon);
        }

        public string do_NameOfStoredProcedure(int parameter)
        {
            con.Open();

            using (SqlCommand cmd = new SqlCommand("NameOfStoredProcedure", con))
            {
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@parameter", parameter);


                using (SqlDataReader reader = cmd.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        json.AppendFormat("[{0},\"{1}\"],", reader["column1"], reader["column2"]);
                    }
                }
                con.Close();
            }

            if (json.Length.ToString().Equals("0"))
            {
                return "[]";
            }

            else
            {
                return "[" + json.ToString().TrimEnd(lastComma) + "]";
            }
        }


        //http://host.com/NameOfStoredProcedure?parameter=value
        public ActionResult Index(int parameter)
        {
            return new ContentResult
            {
                ContentType = "application/json",
                Content = do_NameOfStoredProcedure(parameter)
            };
        }
    }
}