public class NullToEmptyStringResolver : DefaultContractResolver    {        /// 
        /// 创建属性        /// 
        /// 类型        /// 序列化成员        /// 
             protected override IList
     
       CreateProperties(Type type, MemberSerialization memberSerialization)        {            return type.GetProperties()                .Select(x =>                {                    var property = CreateProperty(x, memberSerialization);                    property.ValueProvider = new NullToEmptyStringValueProvider(x);                    return property;                }).ToList();        }        /// 
              /// 
      
        /// 小写        /// 
        /// 
              /// 
              protected override string ResolvePropertyName(string propertyName)        {            return propertyName.ToLower();        }    }
     

public class NullToEmptyStringValueProvider : IValueProvider    {        private readonly PropertyInfo _memberInfo;        /// 
        /// 构造函数        /// 
        ///         public NullToEmptyStringValueProvider(PropertyInfo memberInfo)        {            _memberInfo = memberInfo;        }        /// 
             /// 
        /// 获取Value        /// 
        ///         /// 
             public object GetValue(object target)        {            var result = _memberInfo.GetValue(target);            if (_memberInfo.PropertyType == typeof(string) && result == Convert.DBNull)            {                result = string.Empty;            }            return result;        }        /// 
             /// 
        /// 设置Value        /// 
        ///         ///         public void SetValue(object target, object value)        {            _memberInfo.SetValue(target, value);        }    }