使用JsonConverter處理上傳檔案的路徑問題

/// <summary>
/// 處理圖片檔案字首，資料庫中存相對路徑即可
/// </summary>
public class JsonUrlPrefixConverter : JsonConverter
{
    private string urlPrefix;
    public JsonUrlPrefixConverter()
    {
        urlPrefix ="htttp://www.abc.com"; //這裡字首可以做成設定，換域名時改一下設定即可
    }

    public JsonUrlPrefixConverter(string flag)
    {
        if (flag == "something")
        {
            urlPrefix = "htttp://www.123.com";
        }
    }

    public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
    {
        if (value != null)
        {
            if (value is IEnumerable<string> arr)
            {
                writer.WriteStartArray();
                foreach (var str in arr.Select(x =>
                             x.StartsWith("http", StringComparison.OrdinalIgnoreCase) ? x : urlPrefix + x))
                {
                    writer.WriteValue(str);
                }
                writer.WriteEndArray();
            }
            else if (value is string str && !str.StartsWith("http", StringComparison.OrdinalIgnoreCase))
            {
                if (str.HasValue())
                    str = urlPrefix + str;
                writer.WriteValue(str);
            }
            else
            {
                writer.WriteValue(value);
            }
        }
        else
        {
            writer.WriteValue(value);
        }
    }

    public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue,
        JsonSerializer serializer)
    {
        if (objectType == typeof(string))
        {
            var str = serializer.Deserialize<string>(reader);
            return str;
        }

        if (objectType == typeof(List<string>))
        {
            var list = serializer.Deserialize<List<string>>(reader);

            return list.Select(x => x.Replace(urlPrefix, "")).ToList();
        }

        if (objectType == typeof(string[]))
        {
            var arr = serializer.Deserialize<string[]>(reader);
            return arr.Select(x => x.Replace(urlPrefix, "")).ToArray();
        }

        return reader.Value;
    }

    public override bool CanConvert(Type objectType)
    {
        //請自覺用於 string[]、string、List<string>型別
        return true;
    }
}

builder.Services.AddControllers()
.AddNewtonsoftJson(options =>
{
    //忽略迴圈參照問題
    options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
});

    /// <summary>
    /// 頭像
    /// </summary>
    [JsonConverter(typeof(JsonUrlPrefixConverter))]
    public string Avatar { get; set; } = "";