ASP.NET Core Web API如何导出与导入外部REST API的JSON数据？

需求背景 #

我正在构建ASP.NET Core WebAPI，用于从外部REST API获取JSON格式的天气数据，现在需要实现这些数据的本地保存（导出）和重新加载（导入）功能。

当前获取外部API数据的代码如下：

public async Task<List<Weather>> Get(string cities)
{
    List<Weather> weathers = new List<Weather>(); 
    var options = new JsonSerializerOptions
    {
        PropertyNameCaseInsensitive = true
    };

    foreach (var city in cities.Split(";"))
    {
        string APIURL = $"?key={this.apiKey}&q={city}";
        var response = await _httpClient.GetAsync(APIURL);

        if (response.IsSuccessStatusCode)
        {
            var responses = await response.Content.ReadAsStreamAsync();
            var weather = await JsonSerializer.DeserializeAsync<Weather>(responses, options);

            weathers.Add(weather);
        }

    }

    return weathers;
}

返回的JSON格式示例：

[
   {
      "location":{
         "name":"Chennai",
         "region":"Tamil Nadu",
         ...
      },
      "current":{
         "last_updated_epoch":1663601400,
         "last_updated":"2022-09-19 21:00",
         ...
      }
   },
   {
      "location":{
         "name":"Mumbai",
         "region":"Maharashtra",
         ..
      },
      "current":{
         "last_updated_epoch":1663602300,
         "last_updated":"2022-09-19 21:15",
         ..
      }
   }
]

已实现的代码更新 #

我已经编写了文件操作工具类和导入导出的相关代码，具体如下：

JSON文件操作工具类 #

public static class JsonFileUtils
{
    private static readonly JsonSerializerSettings _options
        = new() { NullValueHandling = NullValueHandling.Ignore };

    public static void StreamWrite(object obj, string fileName)
    {
        using var streamWriter = File.CreateText(fileName);
        using var jsonWriter = new JsonTextWriter(streamWriter);

        JsonSerializer.CreateDefault(_options).Serialize(jsonWriter, obj);
    }

    public static async Task StreamWriteAsync(object obj, string fileName)
    {
        await Task.Run(() => StreamWrite(obj, fileName));
    }
}

数据导出（保存到本地文件） #

在获取数据的接口中添加保存逻辑：

public async Task<List<Weather>> Get(string cities)
{
    List<Weather> weathers = new List<Weather>(); 
    var options = new JsonSerializerOptions
    {
        PropertyNameCaseInsensitive = true
    };

    foreach (var city in cities.Split(";"))
    {
        string APIURL = $"?key={this.apiKey}&q={city}";
        var response = await _httpClient.GetAsync(APIURL);

        if (response.IsSuccessStatusCode)
        {
            var responses = await response.Content.ReadAsStreamAsync();
            var weather = await JsonSerializer.DeserializeAsync<Weather>(responses, options);

            weathers.Add(weather);
        }

    }

    var fileName = "weathers.json";
    await JsonFileUtils.StreamWriteAsync(weathers, fileName);

    return weathers;
}

数据导入（上传JSON文件并解析） #

添加文件上传接口：

[HttpPost("upload", Name = "upload")]
[ProducesResponseType(StatusCodes.Status200OK, Type = typeof(List<Weather>))]
[ProducesResponseType(typeof(string), StatusCodes.Status400BadRequest)]
public async Task<IActionResult> UploadFile(
        IFormFile file,
        CancellationToken cancellationToken)
{
    string fileContent = null;

    using (var reader = new StreamReader(file.OpenReadStream()))
    {
        fileContent = reader.ReadToEnd();
    }
    var result = JsonConvert.DeserializeObject<List<Weather>>(fileContent);
    return Ok(result);
}

代码优化建议 #

• 统一JSON序列化库：当前代码混合使用了System.Text.Json（获取数据时的反序列化）和Newtonsoft.Json（文件操作和上传解析），建议统一使用其中一种，避免配置不一致。比如统一用System.Text.Json重构工具类和上传接口：

  // 重构后的JsonFileUtils
  public static class JsonFileUtils
  {
      private static readonly JsonSerializerOptions _options = new() 
      { 
          NullValueHandling = JsonIgnoreCondition.WhenWritingNull,
          WriteIndented = true,
          PropertyNameCaseInsensitive = true
      };
  
      public static void StreamWrite<T>(T obj, string fileName)
      {
          using var stream = File.Create(fileName);
          JsonSerializer.Serialize(stream, obj, _options);
      }
  
      public static async Task StreamWriteAsync<T>(T obj, string fileName)
      {
          using var stream = File.Create(fileName);
          await JsonSerializer.SerializeAsync(stream, obj, _options);
      }
  
      public static T StreamRead<T>(string fileName)
      {
          using var stream = File.OpenRead(fileName);
          return JsonSerializer.Deserialize<T>(stream, _options);
      }
  
      public static async Task<T> StreamReadAsync<T>(string fileName)
      {
          using var stream = File.OpenRead(fileName);
          return await JsonSerializer.DeserializeAsync<T>(stream, _options);
      }
  }
  

  // 重构后的上传接口
  [HttpPost("upload", Name = "upload")]
  [ProducesResponseType(StatusCodes.Status200OK, Type = typeof(List<Weather>))]
  [ProducesResponseType(typeof(string), StatusCodes.Status400BadRequest)]
  public async Task<IActionResult> UploadFile(
          IFormFile file,
          CancellationToken cancellationToken)
  {
      if (file == null || file.Length == 0)
      {
          return BadRequest("上传的文件不能为空");
      }
  
      var fileExtension = Path.GetExtension(file.FileName).ToLowerInvariant();
      if (fileExtension != ".json")
      {
          return BadRequest("仅支持上传JSON格式文件");
      }
  
      try
      {
          using var stream = file.OpenReadStream();
          var result = await JsonSerializer.DeserializeAsync<List<Weather>>(stream, _options);
          return Ok(result);
      }
      catch (JsonException ex)
      {
          return BadRequest($"JSON格式错误：{ex.Message}");
      }
  }
  

• 规范文件存储路径：直接使用文件名会保存到程序运行目录，建议配置固定存储目录（如wwwroot/weather-data），并确保目录存在：

  private static string GetStoragePath(string fileName)
  {
      var basePath = Path.Combine(Directory.GetCurrentDirectory(), "wwwroot", "weather-data");
      Directory.CreateDirectory(basePath);
      return Path.Combine(basePath, fileName);
  }
  

• 增强错误处理：导出时添加异常捕获，避免保存失败影响接口返回；导入时增加文件校验和格式错误提示，提升接口健壮性。

内容的提问来源于stack exchange，提问作者One Developer