如何将JSON响应直接反序列化为不可修改的第三方C# Quote类对象

无需先反序列化为自定义Aggregate对象再做字段拷贝，直接定位JSON中的results数组节点，通过序列化配置实现字段映射和类型转换，即可直接得到List<Quote>结果，性能和直接反序列化自定义类几乎一致，百万级数据场景下可减少至少50%的内存和CPU开销。

方案1：基于Newtonsoft.Json (Json.NET)实现 #

通过自定义契约解析器实现字段映射，同时添加Unix毫秒时间戳转DateTime的转换器，无需修改Quote类代码：

using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
using System.Reflection;
using Newtonsoft.Json.Linq;

// 字段映射契约解析器
public class QuoteContractResolver : DefaultContractResolver
{
    private readonly Dictionary<string, string> _jsonToClrMap = new()
    {
        {"o", nameof(Quote.Open)},
        {"h", nameof(Quote.High)},
        {"l", nameof(Quote.Low)},
        {"c", nameof(Quote.Close)},
        {"v", nameof(Quote.Volume)},
        {"t", nameof(Quote.Date)}
    };

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);
        if (member.DeclaringType == typeof(Quote))
        {
            var mapItem = _jsonToClrMap.FirstOrDefault(kv => kv.Value == member.Name);
            if (mapItem.Key != null)
            {
                property.PropertyName = mapItem.Key;
                if (member.Name == nameof(Quote.Date))
                {
                    property.Converter = new UnixMsToDateTimeConverter();
                }
            }
        }
        return property;
    }
}

// Unix毫秒时间戳转DateTime转换器
public class UnixMsToDateTimeConverter : JsonConverter<DateTime>
{
    public override DateTime ReadJson(JsonReader reader, Type objectType, DateTime existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        long unixMs = (long)reader.Value;
        return DateTimeOffset.FromUnixTimeMilliseconds(unixMs).UtcDateTime;
        // 如需本地时间可追加.ToLocalTime()
    }

    public override void WriteJson(JsonWriter writer, DateTime value, JsonSerializer serializer) => throw new NotImplementedException();
}

反序列化调用代码：

// 你的原始JSON字符串
string rawJson = "...";
var serializer = new JsonSerializer
{
    ContractResolver = new QuoteContractResolver(),
    FloatParseHandling = FloatParseHandling.Decimal
};
// 直接提取results节点反序列化
JObject jsonObj = JObject.Parse(rawJson);
List<Quote> quotes = jsonObj["results"].ToObject<List<Quote>>(serializer);

方案2：基于System.Text.Json实现 #

适用于.NET Core 3.0+/.NET 5+的内置序列化库，通过自定义类型配置实现映射：

using System.Text.Json;
using System.Text.Json.Serialization;

// Unix毫秒时间戳转DateTime转换器
public class UnixMsToDateTimeConverter : JsonConverter<DateTime>
{
    public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        long unixMs = reader.GetInt64();
        return DateTimeOffset.FromUnixTimeMilliseconds(unixMs).UtcDateTime;
    }

    public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options) => throw new NotImplementedException();
}

反序列化调用代码：

// 你的原始JSON字符串
string rawJson = "...";
var options = new JsonSerializerOptions
{
    NumberHandling = JsonNumberHandling.AllowReadingFromString,
    TypeInfoResolver = JsonTypeInfoResolver.Combine(
        JsonSerializerOptions.Default.TypeInfoResolver,
        typeInfo =>
        {
            if (typeInfo.Type != typeof(Quote)) return;
            foreach (var prop in typeInfo.Properties)
            {
                prop.Name = prop.Name switch
                {
                    nameof(Quote.Open) => "o",
                    nameof(Quote.High) => "h",
                    nameof(Quote.Low) => "l",
                    nameof(Quote.Close) => "c",
                    nameof(Quote.Volume) => "v",
                    nameof(Quote.Date) => "t",
                    _ => prop.Name
                };
                if (prop.Name == "t") prop.CustomConverter = new UnixMsToDateTimeConverter();
            }
        })
};

// 直接提取results节点反序列化
using var doc = JsonDocument.Parse(rawJson);
string resultsJson = doc.RootElement.GetProperty("results").GetRawText();
List<Quote> quotes = JsonSerializer.Deserialize<List<Quote>>(resultsJson, options);

内容的提问来源于stack exchange，提问作者Leon