Question

我想支持使用Newtonsoft Json反序列化器反序列化多个自定义DateTime格式，因此我正在使用IsoDateTimeConverter：

var serializeSettings = new JsonSerializerSettings();
serializeSettings.Converters.Add(new IsoDateTimeConverter() { DateTimeFormat = "yyyyMMddTHHmmssZ" });

由于DateTimeFormat属性不接受格式数组，因此我尝试了以下方法来支持多种自定义日期格式：

var serializeSettings = new JsonSerializerSettings();
serializeSettings.Converters.Add(new IsoDateTimeConverter() { DateTimeFormat = "yyyyMMddTHHmmssZ" });
serializeSettings.Converters.Add(new IsoDateTimeConverter() { DateTimeFormat = "yyyy-MM-ddTHH:mm" });

但是，以上代码的结果仅支持反序列化第一种格式。

如何实现对多种自定义DateTime格式的支持？

Answer 1

如果要处理多种可能的日期格式，则需要制作一个自定义JsonConverter，它可以接受多种格式的字符串，并尝试全部使用，直到成功为止。这是一个简单的示例：

class MultiFormatDateConverter : JsonConverter
{
    public List<string> DateTimeFormats { get; set; }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(DateTime);
    }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        string dateString = (string)reader.Value;
        DateTime date;
        foreach (string format in DateTimeFormats)
        {
            // adjust this as necessary to fit your needs
            if (DateTime.TryParseExact(dateString, format, CultureInfo.InvariantCulture, DateTimeStyles.None, out date))
                return date;
        }
        throw new JsonException("Unable to parse \"" + dateString + "\" as a date.");
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

然后您可以将其添加到您的设置中，如下所示：

var settings = new JsonSerializerSettings();
settings.DateParseHandling = DateParseHandling.None;
settings.Converters.Add(new MultiFormatDateConverter 
{ 
    DateTimeFormats = new List<string> { "yyyyMMddTHHmmssZ", "yyyy-MM-ddTHH:mm" } 
});

提琴：https://dotnetfiddle.net/vOpMEY

Answer 2

我想提出一个同时支持DateTime和DateTimeOffset以及可空性的版本。

using System;
using System.Collections.Generic;
using System.Globalization;
using Newtonsoft.Json;
using Newtonsoft.Json.Converters;

internal class MultiFormatDateConverter : DateTimeConverterBase
{
    public IList<string> DateTimeFormats { get; set; } = new[] { "yyyy-MM-dd" };

    public DateTimeStyles DateTimeStyles { get; set; }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        var val = IsNullableType(objectType);
        if (reader.TokenType == JsonToken.Null)
        {
            if (!val)
            {
                throw new JsonSerializationException(
                    string.Format(CultureInfo.InvariantCulture, "Cannot convert null value to {0}.", objectType));
            }
        }

        Type underlyingObjectType = val ? Nullable.GetUnderlyingType(objectType)! : objectType;
        if (reader.TokenType == JsonToken.Date)
        {
            if (underlyingObjectType == typeof(DateTimeOffset))
            {
                if (!(reader.Value is DateTimeOffset))
                {
                    return new DateTimeOffset((DateTime)reader.Value);
                }

                return reader.Value;
            }

            if (reader.Value is DateTimeOffset)
            {
                return ((DateTimeOffset)reader.Value).DateTime;
            }

            return reader.Value;
        }

        if (reader.TokenType != JsonToken.String)
        {
            var errorMessage = string.Format(
                CultureInfo.InvariantCulture,
                "Unexpected token parsing date. Expected String, got {0}.",
                reader.TokenType);
            throw new JsonSerializationException(errorMessage);
        }

        var dateString = (string)reader.Value;
        if (underlyingObjectType == typeof(DateTimeOffset))
        {
            foreach (var format in this.DateTimeFormats)
            {
                // adjust this as necessary to fit your needs
                if (DateTimeOffset.TryParseExact(dateString, format, CultureInfo.InvariantCulture, this.DateTimeStyles, out var date))
                {
                    return date;
                }
            }
        }

        if (underlyingObjectType == typeof(DateTime))
        {

            foreach (var format in this.DateTimeFormats)
            {
                // adjust this as necessary to fit your needs
                if (DateTime.TryParseExact(dateString, format, CultureInfo.InvariantCulture, this.DateTimeStyles, out var date))
                {
                    return date;
                }
            }
        }

        throw new JsonException("Unable to parse \"" + dateString + "\" as a date.");
    }

    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public static bool IsNullableType(Type t)
    {
        if (t.IsGenericTypeDefinition || t.IsGenericType)
        {
            return t.GetGenericTypeDefinition() == typeof(Nullable<>);
        }

        return false;
    }
}

使用Json.Net反序列化时支持多种自定义DateTime格式

2 个答案: