JSON 值无法转换为 System.Byte[]

Question

在处理字节数组时尝试反序列化以下 JSON 时出现以下异常，这是怎么回事？

public class Program
{
    public static void Main()
    {
        var root = JsonSerializer.Deserialize<JsonRoot>(@"{ ""ByteArray"": [1] } ");
    }

    public class JsonRoot
    {
        public byte[] ByteArray {get;set;}  
    }
}

Unhandled exception. System.Text.Json.JsonException: The JSON value could not be converted to System.Byte[]. Path: $.ByteArray | LineNumber: 0 | BytePositionInLine: 16.
 ---> System.InvalidOperationException: Cannot get the value of a token type 'StartArray' as a string.
   at System.Text.Json.Utf8JsonReader.TryGetBytesFromBase64(Byte[]& value)
   at System.Text.Json.Utf8JsonReader.GetBytesFromBase64()
   at System.Text.Json.Serialization.Converters.JsonConverterByteArray.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options)
   at System.Text.Json.JsonPropertyInfoNotNullable`4.OnRead(ReadStack& state, Utf8JsonReader& reader)
   at System.Text.Json.JsonPropertyInfo.Read(JsonTokenType tokenType, ReadStack& state, Utf8JsonReader& reader)
   at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& readStack, Utf8JsonReader& reader, Exception ex)
   at System.Text.Json.JsonSerializer.ReadCore(JsonSerializerOptions options, Utf8JsonReader& reader, ReadStack& readStack)
   at System.Text.Json.JsonSerializer.ReadCore(Type returnType, JsonSerializerOptions options, Utf8JsonReader& reader)
   at System.Text.Json.JsonSerializer.Deserialize(String json, Type returnType, JsonSerializerOptions options)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
   at Program.Main()
Command terminated by signal 6

Answer 1

使用Sytem.Text.Json 字节数组 (byte[]) 将被序列化为 base64 字符串。他们表示不会添加对 byte[] 的支持，以将其序列化为 github issue 中的数字数组。

这是一个可以帮助您入门的自定义转换器。也许您可以稍微优化一下读数，但这种方法对性能的影响应该不会太差。您可能想要添加 null 和错误处理，但您明白了。

要应用自定义转换器，您必须将它们添加到 JsonSerializerOptions。请参考this docs page。

public class ByteArrayConverter : JsonConverter<byte[]>
{
    public override byte[] Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        short[] sByteArray = JsonSerializer.Deserialize<short[]>(ref reader);
        byte[] value = new byte[sByteArray.Length];
        for (int i = 0; i < sByteArray.Length; i++)
        {
            value[i] = (byte)sByteArray[i];
        }

        return value;
    }

    public override void Write(Utf8JsonWriter writer, byte[] value, JsonSerializerOptions options)
    {
        writer.WriteStartArray();

        foreach (var val in value)
        {
            writer.WriteNumberValue(val);
        }

        writer.WriteEndArray();
    }
}