Json.net 的自訂 Serialize 與 Deserialize

Json.net 的自訂序列化與反序列化

會使用 Json.net 此自訂序列化 (Serialize) 或是 反序列化 (Deserialize) 的原因主要是希望在序列化 Json 的時候，可以直接將時間的部分按照客戶要求輸出

先附上使用環境與套件版本

• Newtonsoft.Json 版本 : 10.0.2
• 編輯器 LINQPad 版本 : 5.31.00(AnyCPU)

首先建立一個範例 Class 叫做 SampleModel ，然後利用時區讓兩個 DateTime 格式的屬性來做範例輸出

void Main()
{
  SampleModel model = new SampleModel();
  
  // 格式化輸出
  var indented = Newtonsoft.Json.Formatting.Indented;

  var jsonModel = JsonConvert.SerializeObject(model, indented);
  jsonModel.Dump();
}

/// <summary>
/// Class SampleModel.
/// </summary>
public class SampleModel
{
  public int Id { get; set; } = 1;
  public DateTime UtcDate { get; set; } = DateTime.UtcNow;
  public DateTime NowDate { get; set; } = DateTime.Now;
}

序列化

承襲上述的 SampleModel ，此部分針對 Json.net 的 JsonConverter 來自訂規則，主要需要撰寫的部分有 CanConvert 與 WriteJson 兩個方法

void Main()
{
  SampleModel model = new SampleModel();
  // 格式化輸出
  var indented = Newtonsoft.Json.Formatting.Indented;

  // 設定自訂規則轉換 DateTime 格式
  var jsonModel = JsonConvert.SerializeObject(model, indented, new SampleModelConverter(typeof(DateTime)));
  jsonModel.Dump();
}

// Class SampleModel. 請參照上述，此處省略

/// <summary>
/// Class SampleModelConverter.
/// </summary>
/// <seealso cref="Newtonsoft.Json.JsonConverter" />
public class SampleModelConverter : JsonConverter
{
  private readonly Type[] _types;

  /// <summary>
  /// 建構式
  /// </summary>
  /// <param name="types">The types.</param>
  public SampleModelConverter(params Type[] types)
  {
    _types = types;
  }

  /// <summary>
  /// Writes the JSON representation of the object.
  /// </summary>
  /// <param name="writer">The <see cref="T:Newtonsoft.Json.JsonWriter" /> to write to.</param>
  /// <param name="value">The value.</param>
  /// <param name="serializer">The calling serializer.</param>
  public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
  {
    Type type = value.GetType();
    if (type == typeof(DateTime))
    {
      var date = (DateTime)value;
      serializer.Serialize(writer, date.ToLocalTime().ToString("yyyy-MM-dd hh:mm:ss"));

      // 想寫入 json 物件，使用以下語法
      // writer.WriteStartObject();
      // writer.WritePropertyName(type.Name);
      // writer.WriteEndObject();
    }
  }

  /// <summary>
  /// Reads the JSON representation of the object.
  /// </summary>
  /// <param name="reader">The <see cref="T:Newtonsoft.Json.JsonReader" /> to read from.</param>
  /// <param name="objectType">Type of the object.</param>
  /// <param name="existingValue">The existing value of object being read.</param>
  /// <param name="serializer">The calling serializer.</param>
  /// <returns>The object value.</returns>
  public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
  {
    return null;
  }

  /// <summary>
  /// 判斷此物件是否符合自訂規則的設定型別，符合即可進行轉換
  /// </summary>
  /// <param name="objectType">Type of the object.</param>
  /// <returns><c>true</c> if this instance can convert the specified object type; otherwise, <c>false</c>.</returns>
  public override bool CanConvert(Type objectType)
  {
    var result = _types.Any(t => t == objectType);
    return result;
  }
}

Deserialize反序列化

反序列化要注意的是要自訂 ReadJson 這個方法

void Main()
{
  SampleModel model = new SampleModel();
  // 格式化輸出
  var indented = Newtonsoft.Json.Formatting.Indented;

  // 設定自訂規則轉換 DateTime 格式
  var jsonModel = JsonConvert.SerializeObject(model, indented, new SampleModelConverter(typeof(DateTime)));
  jsonModel.Dump();

  // 設定自訂規則轉換 DateTime 格式
  var deserializeJson = JsonConvert.DeserializeObject<SampleModel>(jsonModel, new SampleModelConverter(typeof(DateTime)));
  deserializeJson.Dump();

}

// Class SampleModel. 請參照上述，此處省略

/// <summary>
/// Class SampleModelConverter.
/// </summary>
/// <seealso cref="Newtonsoft.Json.JsonConverter" />
public class SampleModelConverter : JsonConverter
{
  // ... 其他方法與屬性同序列化的自訂，除 ReadJson 方法不同

  /// <summary>
  /// Reads the JSON representation of the object.
  /// </summary>
  /// <param name="reader">The <see cref="T:Newtonsoft.Json.JsonReader" /> to read from.</param>
  /// <param name="objectType">Type of the object.</param>
  /// <param name="existingValue">The existing value of object being read.</param>
  /// <param name="serializer">The calling serializer.</param>
  /// <returns>The object value.</returns>
  public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
  {
    // reader Json 讀取出來的類型為 Date 格式就進行轉換
    // 當序列化使用此規則時，此處可以省略，因為會沒有 Date 格式
    if (reader.TokenType == JsonToken.Date)
    {
      return ((DateTime)existingValue).ToLocalTime();
    }

    if (DateTime.TryParse(existingValue.ToString(), out DateTime dateValue))
    {
      return dateValue.ToLocalTime();
    }

    return null;
  }
}

總結

Json.net 的 JsonConverter 訂立的規則是通用的，不是針對單一型別的規則，當然此範例還可以使用 *JsonSerializer.DateFormatString * 等各種方式達到目的，不過此範例重點在於自訂規則與轉換型別的部分，最後附上完整的 sample code

void Main()
{
  SampleModel model = new SampleModel();

  // 格式化輸出
  var indented = Newtonsoft.Json.Formatting.Indented;

  var jsonModel = JsonConvert.SerializeObject(model, indented, new SampleModelConverter(typeof(DateTime)));
  jsonModel.Dump();

  var deserializeJson = JsonConvert.DeserializeObject<SampleModel>(jsonModel, new SampleModelConverter(typeof(DateTime)));
  deserializeJson.Dump();
}

/// <summary>
/// Class SampleModel.
/// </summary>
public class SampleModel
{
  public int Id { get; set; } = 1;
  public DateTime UtcDate { get; set; } = DateTime.UtcNow;
  public DateTime NowDate { get; set; } = DateTime.Now;
}

/// <summary>
/// Class SampleModelConverter.
/// </summary>
/// <seealso cref="Newtonsoft.Json.JsonConverter" />
public class SampleModelConverter : JsonConverter
{
  private readonly Type[] _types;

  /// <summary>
  /// Initializes a new instance of the <see cref="SampleModelConverter"/> class.
  /// </summary>
  /// <param name="types">The types.</param>
  public SampleModelConverter(params Type[] types)
  {
    _types = types;
  }

  /// <summary>
  /// Writes the JSON representation of the object.
  /// </summary>
  /// <param name="writer">The <see cref="T:Newtonsoft.Json.JsonWriter" /> to write to.</param>
  /// <param name="value">The value.</param>
  /// <param name="serializer">The calling serializer.</param>
  public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
  {
    Type type = value.GetType();
    if (type == typeof(DateTime))
    {
      var date = (DateTime)value;
      serializer.Serialize(writer, date.ToLocalTime().ToString("yyyy-MM-dd hh:mm:ss"));
    }
  }

  /// <summary>
  /// Reads the JSON representation of the object.
  /// </summary>
  /// <param name="reader">The <see cref="T:Newtonsoft.Json.JsonReader" /> to read from.</param>
  /// <param name="objectType">Type of the object.</param>
  /// <param name="existingValue">The existing value of object being read.</param>
  /// <param name="serializer">The calling serializer.</param>
  /// <returns>The object value.</returns>
  public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
  {
    if (reader.TokenType == JsonToken.Date)
    {
      return ((DateTime)existingValue).ToLocalTime();
    }
    if (DateTime.TryParse(existingValue.ToString(), out DateTime dateValue))
    {
      return dateValue.ToLocalTime();
    }
    return null;
  }

  /// <summary>
  /// 判斷此物件是否符合自訂規則的設定型別，符合即可進行轉換
  /// </summary>
  /// <param name="objectType">Type of the object.</param>
  /// <returns><c>true</c> if this instance can convert the specified object type; otherwise, <c>false</c>.</returns>
  public override bool CanConvert(Type objectType)
  {
    var result = _types.Any(t => t == objectType);
    return result;
  }
}

延伸閱讀

文中的時區轉換都比較偷懶，都是使用 ToLocalTime 等方式處理，要執行轉換的話，建議可以使用 TimeZoneInfo 來轉換，如下範例

var twtzinfo = TimeZoneInfo.FindSystemTimeZoneById("Taipei Standard Time");
DateTime localdt = TimeZoneInfo.ConvertTime(DateTime.UtcNow,TimeZoneInfo.Utc, twtzinfo);
DateTime localdt2 = TimeZoneInfo.ConvertTime(DateTime.UtcNow, twtzinfo);
DateTime localdt3 = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, twtzinfo);
localdt.Dump();
localdt2.Dump();
localdt3.Dump();

附上拉取時區名稱與時區 ID 的作法，或是參考 microsoft 時區 ID 文件

TimeZoneInfo localZone = TimeZoneInfo.Local;

Dictionary<string, string> timeZoneIdName = new Dictionary<string, string>()
{
  { localZone.Id, localZone.DisplayName}
};

timeZoneIdName.Dump();
ReadOnlyCollection<TimeZoneInfo> list = TimeZoneInfo.GetSystemTimeZones();
foreach (var zone in list)
{
  if (!timeZoneIdName.ContainsKey(zone.Id))
    timeZoneIdName.Add(zone.Id, zone.DisplayName);
}

timeZoneIdName.Dump();

• microsoft docs 時區轉換時間
• Newtonsoft DeserializeDateFormatString
• Newtonsoft CustomJsonConverter
• microsoft 時區 ID 參考
• Will 保哥 .NET 日期結構(DateTime) 與 時區轉換
• Darkthread DateTime時區與比較
• Bulletproof Interface Deserialization in Json.NET
• Using custom converters in JSON.NET: Array or Object?
• JSON.NET Implementing Custom Serialization
• Encrypting values when serializing with JSON.NET
• Github 上的 Serialization