如何在c#中读取一个非常大的JSON文件到一个数组中,以便拆分以供以后处理?


我已经设法得到一些工作,将:

读取文件忽略头文件,只将值读入数组。 在数组的每一行上放置一定数量的值。(所以我 可以稍后将其分割成一个放入2d数组)

这是用下面的代码完成的,但是在数组中输入几行后程序就崩溃了。这可能与文件大小有关。

// If the file extension was a jave file the following 
// load method will be use else it will move on to the 
// next else if statement
if (fileExtension == ".json") 
{
    int count = 0;
    int count2 = 0;
    int inOrOut = 0;
    int nRecords=1; 
    JsonTextReader reader = new JsonTextReader(new StreamReader(txtLoaction.Text));
    string[] rawData = new string[5];
    while (reader.Read())
    {
        if (reader.Value != null)
            if (inOrOut == 1)
            {
                if (count == 6)
                {
                    nRecords++;
                    Array.Resize(ref rawData, nRecords);
                    //textBox1.Text += "\r\n";
                    count = 0;
                }
                rawData[count2] += reader.Value + ","; //+"\r\n"
                inOrOut = 0;
                count++;
                if (count2 == 500)
                {
                    MessageBox.Show(rawData[499]);
                }
            }
            else
            {
                inOrOut = 1;
            }
    } 
}

我正在使用的JSON片段是:

[ 
    { "millis": "1000", 
      "stamp": "1273010254", 
      "datetime": "2010/5/4 21:57:34", 
      "light": "333", 
      "temp": "78.32", 
      "vcc": "3.54" }, 
] 

我需要这个JSON的值。例如,我需要“3.54”,但我不希望它打印“vcc”。

如何读取JSON文件,只提取需要放入数组的数据?


当前回答

Doing this yourself is an awful idea. Use Json.NET. It has already solved the problem better than most programmers could if they were given months on end to work on it. As for your specific needs, parsing into arrays and such, check the documentation, particularly on JsonTextReader. Basically, Json.NET handles JSON arrays natively and will parse them into strings, ints, or whatever the type happens to be without prompting from you. Here is a direct link to the basic code usages for both the reader and the writer, so you can have that open in a spare window while you're learning to work with this.

这是最好的:这次偷懒,使用一个库,这样你就永远解决了这个常见的问题。

其他回答

Doing this yourself is an awful idea. Use Json.NET. It has already solved the problem better than most programmers could if they were given months on end to work on it. As for your specific needs, parsing into arrays and such, check the documentation, particularly on JsonTextReader. Basically, Json.NET handles JSON arrays natively and will parse them into strings, ints, or whatever the type happens to be without prompting from you. Here is a direct link to the basic code usages for both the reader and the writer, so you can have that open in a spare window while you're learning to work with this.

这是最好的:这次偷懒,使用一个库,这样你就永远解决了这个常见的问题。

用Json.NET让一切变得更简单怎么样?

    public void LoadJson()
    {
        using (StreamReader r = new StreamReader("file.json"))
        {
            string json = r.ReadToEnd();
            List<Item> items = JsonConvert.DeserializeObject<List<Item>>(json);
        }
    }

    public class Item
    {
        public int millis;
        public string stamp;
        public DateTime datetime;
        public string light;
        public float temp;
        public float vcc;
    }

您甚至可以在不声明Item类的情况下动态地获取值。

    dynamic array = JsonConvert.DeserializeObject(json);
    foreach(var item in array)
    {
        Console.WriteLine("{0} {1}", item.temp, item.vcc);
    }

为我找到了正确的道路

   var pathToJson = Path.Combine("my","path","config","default.Business.Area.json");
   var r = new StreamReader(pathToJson);
   var myJson = r.ReadToEnd();

   // my/path/config/default.Business.Area.json 
   [...] do parsing here 

路径。Combine使用路径。它检查第一个路径的末尾是否已经有分隔符,这样它就不会复制分隔符。此外,它还检查要组合的路径元素是否具有无效字符。

参见https://stackoverflow.com/a/32071002/4420355

.NET核心的答案

你可以使用内置的System.Text.Json而不是第三方的Json.NET。为了促进重用,json文件读取功能属于自己的类,应该是泛型的,而不是硬编码为某种类型(Item)。下面是一个完整的例子:

using System;
using System.IO;
using System.Text.Json;
using System.Threading.Tasks;

namespace Project
{
    class Program
    {
        static async Task Main()
        {
            Item item = await JsonFileReader.ReadAsync<Item>(@"C:\myFile.json");
        }
    }

    public static class JsonFileReader
    {
        public static async Task<T> ReadAsync<T>(string filePath)
        {
            using FileStream stream = File.OpenRead(filePath);
            return await JsonSerializer.DeserializeAsync<T>(stream);
        }
    }

    public class Item
    {
        public int millis;
        public string stamp;
        public DateTime datetime;
        public string light;
        public float temp;
        public float vcc;
    }
}

或者,如果你更喜欢简单的/同步的:

class Program
{
    static void Main()
    {
        Item item = JsonFileReader.Read<Item>(@"C:\myFile.json");
    }
}

public static class JsonFileReader
{
    public static T Read<T>(string filePath)
    {
        string text = File.ReadAllText(filePath);
        return JsonSerializer.Deserialize<T>(text);
    }
}

基于@ l.b.。的解决方案,(类型为对象而不是匿名)VB代码是

Dim oJson As Object = JsonConvert.DeserializeObject(File.ReadAllText(MyFilePath))

我应该提到,对于构造不需要类型的HTTP调用内容,这是快速且有用的。使用对象而不是匿名意味着你可以在Visual Studio环境中保持Option Strict On -我讨厌关闭它。