問題描述

到目前為止，我已經使用了 Json.NET 的JsonConvert.Deserialize(json)"方法，效果很好，老實說，我不需要更多的東西.

I have used the "JsonConvert.Deserialize(json)" method of Json.NET so far which worked quite well and to be honest, I didn't need anything more than this.

我正在開發一個后臺(控制臺)應用程序，該應用程序不斷從不同的 URL 下載 JSON 內容，然后將結果反序列化為 .NET 對象列表.

I am working on a background (console) application which constantly downloads the JSON content from different URLs, then deserializes the result into a list of .NET objects.

 using (WebClient client = new WebClient())
 {
      string json = client.DownloadString(stringUrl);

      var result = JsonConvert.DeserializeObject<List<Contact>>(json);

 }

上面的簡單代碼片段可能看起來并不完美，但它確實可以完成工作.當文件很大(15,000 個聯系人 - 48 MB 文件)時，JsonConvert.DeserializeObject 不是解決方案，并且該行會引發 JsonReaderException 異常類型.

The simple code snippet above doesn't probably seem perfect, but it does the job. When the file is large (15,000 contacts - 48 MB file), JsonConvert.DeserializeObject isn't the solution and the line throws an exception type of JsonReaderException.

下載的 JSON 內容是一個數組，這就是示例的樣子.Contact 是反序列化 JSON 對象的容器類.

The downloaded JSON content is an array and this is how a sample looks like. Contact is a container class for the deserialized JSON object.

[
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  }
]

我最初的猜測是內存不足.只是出于好奇，我嘗試將其解析為 JArray，這也導致了同樣的異常.

My initial guess is it runs out of memory. Just out of curiosity, I tried to parse it as JArray which caused the same exception too.

我已經開始深入研究 Json.NET 文檔并閱讀類似的主題.由于我還沒有設法產生一個可行的解決方案，我決定在這里發布一個問題.

I have started to dive into Json.NET documentation and read similar threads. As I haven't managed to produce a working solution yet, I decided to post a question here.

更新:在逐行反序列化時，我得到了同樣的錯誤:[.Path '', line 600003, position 1."所以下載了其中兩個并在記事本++中檢查了它們.我注意到如果數組長度超過 12,000，則在第 12000 個元素之后，["關閉，另一個數組開始.換句話說，JSON 看起來就像這樣:

UPDATE: While deserializing line by line, I got the same error: " [. Path '', line 600003, position 1." So downloaded two of them and checked them in Notepad++. I noticed that if the array length is more than 12,000, after 12000th element, the "[" is closed and another array starts. In other words, the JSON looks exactly like this:

[
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  }
]
[
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  },
  {
    "firstname": "sometext",
    "lastname": "sometext"
  }
]

推薦答案

正如您在更新中正確診斷的那樣，問題是 JSON 有一個結束 ] 緊跟一個開始 [ 開始下一組.這種格式在整體上會使 JSON 無效，這就是 Json.NET 拋出錯誤的原因.

As you've correctly diagnosed in your update, the issue is that the JSON has a closing ] followed immediately by an opening [ to start the next set. This format makes the JSON invalid when taken as a whole, and that is why Json.NET throws an error.

幸運的是，這個問題似乎經常出現，以至于 Json.NET 實際上有一個特殊的設置來處理它.如果直接使用 JsonTextReader 讀取 JSON，可以將 SupportMultipleContent 標志設置為 true，然后使用循環反序列化每個項個人.

Fortunately, this problem seems to come up often enough that Json.NET actually has a special setting to deal with it. If you use a JsonTextReader directly to read the JSON, you can set the SupportMultipleContent flag to true, and then use a loop to deserialize each item individually.

這應該允許您以高效的內存方式成功處理非標準 JSON，而不管有多少數組或每個數組中有多少項.

This should allow you to process the non-standard JSON successfully and in a memory efficient manner, regardless of how many arrays there are or how many items in each array.

    using (WebClient client = new WebClient())
    using (Stream stream = client.OpenRead(stringUrl))
    using (StreamReader streamReader = new StreamReader(stream))
    using (JsonTextReader reader = new JsonTextReader(streamReader))
    {
        reader.SupportMultipleContent = true;

        var serializer = new JsonSerializer();
        while (reader.Read())
        {
            if (reader.TokenType == JsonToken.StartObject)
            {
                Contact c = serializer.Deserialize<Contact>(reader);
                Console.WriteLine(c.FirstName + " " + c.LastName);
            }
        }
    }

完整演示:https://dotnetfiddle.net/2TQa8p

這篇關于在 .NET 中解析大型 JSON 文件的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！