DataTable转Json字符串

public String ToJson(DataTable tbl)
        {
            if (tbl.Rows.Count > 0)
            {
                DataRowCollection rows = tbl.Rows;
                StringBuilder sb = new StringBuilder();
                sb.Append("[");
                int rowcount = 0;
                int columnCount = 0;
                foreach (DataRow row in tbl.Rows)
                {
                    rowcount++;
                    sb.Append("{");
                    foreach (DataColumn column in tbl.Columns)
                    {
                        columnCount++;
                        sb.AppendFormat("{0}:'{1}'{2}", column.ColumnName, row[column.ColumnName].ToString(), columnCount == tbl.Columns.Count ? "" : ",");
                    }
                    columnCount = 0;
                    sb.Append("}");
                    sb.AppendFormat("{0}", rowcount == tbl.Rows.Count ? "" : ",");
                }
                sb.Append("]");
                return sb.ToString();
            }
            else
            {
                return "";
            }
        }