NewtonSoft.Json NULL转空字符串

from:http://www.cnblogs.com/hetuan/articles/4565702.html

NewtonSoft.Json对需要转为JSON字符串的对象的NULL值以及DBNull是直接处理成NULL的。对DBNull 的JSON字符串对应需要空字符串。

/// <summary>
    /// 对DBNull的转换处理，此处只写了转换成JSON字符串的处理，JSON字符串转对象的未处理
    /// </summary>
    public class DBNullCreationConverter : JsonConverter
    {
        /// <summary>
        /// 是否允许转换
        /// </summary>
        public override bool CanConvert(Type objectType)
        {
            bool canConvert = false;
            switch (objectType.FullName)
            {
                case "System.DBNull":

                    canConvert = true;
                    break;
            }
            return canConvert;
        }

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
        {
            return existingValue;
        }

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
        {
            writer.WriteValue(string.Empty);
        }

        public override bool CanRead
        {
            get
            {
                return false;
            }
        }
        /// <summary>
        /// 是否允许转换JSON字符串时调用
        /// </summary>
        public override bool CanWrite
        {
            get
            {
                return true;
            }
        }
    }

　　

使用：

 IsoDateTimeConverter timeFormat = new IsoDateTimeConverter();
            DBNullCreationConverter x = new DBNullCreationConverter();
            timeFormat.DateTimeFormat = "yyyy-MM-dd HH:mm:ss";

            return JsonConvert.SerializeObject(ds.Tables, Newtonsoft.Json.Formatting.Indented, timeFormat, x);