在System.Text.Json中多态反序列化是可能的吗？

在System.Text.Json中进行多态反序列化是可能的，但需要一些额外的步骤来实现。System.Text.Json本身并不直接支持多态反序列化，因为它不像Newtonsoft.Json（Json.NET）那样内置了对多态类型的支持。但是，你可以通过以下几种方法来实现多态反序列化：

方法一：使用JsonConverter

你可以创建一个自定义的JsonConverter来处理多态类型的反序列化。以下是一个简单的示例：

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

public class Animal
{
    public string Name { get; set; }
}

public class Dog : Animal
{
    public string Breed { get; set; }
}

public class Cat : Animal
{
    public string Color { get; set; }
}

public class AnimalConverter : JsonConverter<Animal>
{
    public override Animal Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        if (reader.TokenType != JsonTokenType.StartObject)
        {
            throw new JsonException();
        }

        reader.Read(); // Move to the first property

        if (reader.TokenType != JsonTokenType.PropertyName)
        {
            throw new JsonException();
        }

        string typeName = reader.GetString();
        reader.Read(); // Move to the value of the property

        Animal animal = null;

        switch (typeName)
        {
            case "Dog":
                animal = JsonSerializer.Deserialize<Dog>(reader.GetString(), options);
                break;
            case "Cat":
                animal = JsonSerializer.Deserialize<Cat>(reader.GetString(), options);
                break;
            default:
                throw new JsonException($"Unknown type: {typeName}");
        }

        reader.Read(); // Move to the end object
        return animal;
    }

    public override void Write(Utf8JsonWriter writer, Animal value, JsonSerializerOptions options)
    {
        throw new NotImplementedException();
    }
}

public class Program
{
    public static void Main()
    {
        string json = @"{""Type"":""Dog"",""Name"":""Buddy"",""Breed"":""Golden Retriever""}";

        var options = new JsonSerializerOptions
        {
            Converters = { new AnimalConverter() }
        };

        Animal animal = JsonSerializer.Deserialize<Animal>(json, options);

        Console.WriteLine(animal.Name);
    }
}

方法二：使用JsonElement和JsonDocument

你可以使用JsonElement和JsonDocument来手动解析JSON并创建相应的对象。以下是一个示例：

using System;
using System.Text.Json;

public class Animal
{
    public string Name { get; set; }
}

public class Dog : Animal
{
    public string Breed { get; set; }
}

public class Cat : Animal
{
    public string Color { get; set; }
}

public class Program
{
    public static void Main()
    {
        string json = @"{""Type"":""Dog"",""Name"":""Buddy"",""Bephel"":""Golden Retriever""}";

        var jsonElement = JsonDocument.Parse(json).RootElement;
        Animal animal = null;

        switch (jsonElement.GetProperty("Type").GetString())
        {
            case "Dog":
                animal = JsonSerializer.Deserialize<Dog>(json);
                break;
            case "Cat":
                animal = JsonSerializer.Deserialize<Cat>(json);
                break;
            default:
                throw new Exception($"Unknown type");
        }

        Console.WriteLine(animal.Name);
    }
}