public static string DataTable2Json(System.Data.DataTable dt)
        {
            System.Text.StringBuilder jsonBuilder = new System.Text.StringBuilder();
            jsonBuilder.Append("{");
            jsonBuilder.AppendFormat("\"total\":{0}, ", dt.Rows.Count);
            jsonBuilder.Append("\"rows\":[ ");
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                jsonBuilder.Append("{");
                for (int j = 0; j < dt.Columns.Count; j++)
                {
                    jsonBuilder.Append("\"");
                    jsonBuilder.Append(dt.Columns[j].ColumnName);
                    jsonBuilder.Append("\":\"");
                    jsonBuilder.Append(dt.Rows[i][j].ToString());
                    jsonBuilder.Append("\",");
                }
                jsonBuilder.Remove(jsonBuilder.Length - 1, 1);
                jsonBuilder.Append("},");
            }
            jsonBuilder.Remove(jsonBuilder.Length - 1, 1);
            jsonBuilder.Append("]");
            jsonBuilder.Append("}");
            return jsonBuilder.ToString();
        }

  int pagNum = int.Parse(Request["page"].ToString());
            int pageSize = int.Parse(Request["rows"].ToString());
            string jsonStr = string.Empty;
            UserInfoDataContextDataContext dbContext = new UserInfoDataContextDataContext("server=.;database=NorthWind;uid=sa;pwd=123456");
            var userInfoLst = dbContext.UserInfo.Take(pageSize * pagNum).Skip((pagNum - 1) * pageSize).Select(s => s);
            jsonStr = JsonHelper.ToJson(userInfoLst);
            System.Text.StringBuilder jsonBuilder = new System.Text.StringBuilder();
            jsonBuilder.Append("{");
            jsonBuilder.AppendFormat("\"total\":{0}, ", dbContext.UserInfo.Count());
            jsonBuilder.Append("\"rows\":");
            jsonBuilder.AppendFormat("{0}", jsonStr);
            jsonBuilder.Append("}");
            return Content(jsonBuilder.ToString());

    /// <summary>
    /// Json数据转换封装
    /// </summary>
    public static class JsonHelper
    {
        public static String ToJson(object obj)
        {
            return Newtonsoft.Json.JsonConvert.SerializeObject(obj);
        }
   }