使用 System.Text.Json 反序列化 Json 时间戳

Question

我正在尝试反序列化以下 JSON

{"serverTime":1613967667240}

进入以下类的对象

public class ApiServerTime
{
    [JsonPropertyName("serverTime")]
    public DateTime ServerTime
    {
        get;
        private set;
    }
}

使用以下命令：

JsonSerializer.Deserialize<ApiServerTime>(jsonString);

但生成的对象包含ServerTime == DateTime.MinValue. 我究竟做错了什么？

Answer 1

您还可以为 System.Text.Json 注册自定义日期格式化程序。 https://learn.microsoft.com/en-us/dotnet/standard/datetime/system-text-json-support

public class DateTimeConverterForCustomStandardFormatR : JsonConverter<DateTime>
{
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        return DateTime.UnixEpoch.AddMilliseconds(reader.GetInt64());
    }

    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options)
    {
        // The "R" standard format will always be 29 bytes.
        Span<byte> utf8Date = new byte[29];

        bool result = Utf8Formatter.TryFormat(value, utf8Date, out _, new StandardFormat('R'));
        Debug.Assert(result);

        writer.WriteStringValue(utf8Date);
    }
}


string js = "{\"ServerTime\":1613967667240}";
JsonSerializerOptions options = new JsonSerializerOptions();
options.Converters.Add(new DateTimeConverterForCustomStandardFormatR());
var value = JsonSerializer.Deserialize<ApiServerTime>(js, options);

Answer 2

本着构建更好的捕鼠器的精神，这里有一个支持的实现。

• 以秒为单位的 Unix 时间或毫秒，取决于以秒为单位的值是否可以在 .net DateTime 最小/最大范围（1/1/0001 到 31/12/9999）内表示。
• Nullable DateTime 可优雅地满足无效、空和 null 值的需求。

public class UnixToNullableDateTimeConverter : JsonConverter<DateTime?>
{
    public bool? IsFormatInSeconds { get; init; }

    public override DateTime? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        try
        {
            if (reader.TryGetInt64(out var time))
            {
                // if 'IsFormatInSeconds' is unspecified, then deduce the correct type based on whether it can be represented as seconds within the .net DateTime min/max range (1/1/0001 to 31/12/9999)
                // - because we're dealing with a 64bit value, the unix time in seconds can exceed the traditional 32bit min/max restrictions (1/1/1970 to 19/1/2038)
                if (IsFormatInSeconds == true || IsFormatInSeconds == null && time > _unixMinSeconds && time < _unixMaxSeconds)
                    return DateTimeOffset.FromUnixTimeSeconds(time).LocalDateTime;
                return DateTimeOffset.FromUnixTimeMilliseconds(time).LocalDateTime;
            }
        }
        catch
        {
            // despite the method prefix 'Try', TryGetInt64 will throw an exception if the token isn't a number.. hence we swallow it and return null
        }
        
        return null;
    }

    // write is out of scope, but this could be implemented via writer.ToUnixTimeMilliseconds/WriteNullValue
    public override void Write(Utf8JsonWriter writer, DateTime? value, JsonSerializerOptions options) => throw new NotSupportedException();

    private static readonly long _unixMinSeconds = DateTimeOffset.MinValue.ToUnixTimeSeconds(); // -62_135_596_800
    private static readonly long _unixMaxSeconds = DateTimeOffset.MaxValue.ToUnixTimeSeconds(); // 253_402_300_799
}