DataSet 转成 JSON 操作类

using  System;
using  System.Collections.Generic;
using  System.Web;
using  System.Data;
using  Newtonsoft.Json;
using  System.Text;
using  System.IO;

     ///   <summary>
     /// JsonHelper 的摘要说明
     ///   </summary>
     public   class  JsonHelper
    {
         public  JsonHelper()
        {
             //
             // TODO: 在此处添加构造函数逻辑
             //
        }

         public   static   string  DataTableToJSON(DataTable dt,  string  dtName)
        {
            StringBuilder sb  =   new  StringBuilder();
            StringWriter sw  =   new  StringWriter(sb);

             using  (JsonWriter jw  =   new  JsonTextWriter(sw))
            {
                JsonSerializer ser  =   new  JsonSerializer();
                jw.WriteStartObject();
                jw.WritePropertyName(dtName);
                jw.WriteStartArray();
                 foreach  (DataRow dr  in  dt.Rows)
                {
                    jw.WriteStartObject();

                     foreach  (DataColumn dc  in  dt.Columns)
                    {
                        jw.WritePropertyName(dc.ColumnName);
                        ser.Serialize(jw, dr[dc].ToString());
                    }

                    jw.WriteEndObject();
                }
                jw.WriteEndArray();
                jw.WriteEndObject();

                sw.Close();
                jw.Close();

            }

             return  sb.ToString();
        }
    }