Json文件讀寫技術

獲取目錄

String dir = Environment.CurrentDirectory    //當前應用程序的路徑，最後不包含'\';

讀寫JSON文件

本程序利用Newtonsoft讀寫Json，下載地址如下：
Newtonsoft

讀取的示例代碼：

using Newtonsoft.Json;

string json = @"{
   'CPU': 'Intel',
   'PSU': '500W',
   'Drives': [
     'DVD read/writer'
     /*(broken)*/,
     '500 gigabyte hard drive',
     '200 gigabyte hard drive'
   ]
}";

JsonTextReader reader = new JsonTextReader(new StringReader(json));
while (reader.Read())
{
    if (reader.Value != null)
    {
        Console.WriteLine("Token: {0}, Value: {1}", reader.TokenType, reader.Value);
    }
    else
    {
        Console.WriteLine("Token: {0}", reader.TokenType);
    }
}

// Token: StartObject
// Token: PropertyName, Value: CPU
// Token: String, Value: Intel
// Token: PropertyName, Value: PSU
// Token: String, Value: 500W
// Token: PropertyName, Value: Drives
// Token: StartArray
// Token: String, Value: DVD read/writer
// Token: Comment, Value: (broken)
// Token: String, Value: 500 gigabyte hard drive
// Token: String, Value: 200 gigabyte hard drive
// Token: EndArray
// Token: EndObject

寫入的代碼：

StringBuilder sb = new StringBuilder();
StringWriter sw = new StringWriter(sb);

using (JsonWriter writer = new JsonTextWriter(sw))
{
    writer.Formatting = Formatting.Indented;

    writer.WriteStartObject();
    writer.WritePropertyName("CPU");
    writer.WriteValue("Intel");
    writer.WritePropertyName("PSU");
    writer.WriteValue("500W");
    writer.WritePropertyName("Drives");
    writer.WriteStartArray();
    writer.WriteValue("DVD read/writer");
    writer.WriteComment("(broken)");
    writer.WriteValue("500 gigabyte hard drive");
    writer.WriteValue("200 gigabyte hard drive");
    writer.WriteEnd();
    writer.WriteEndObject();
}

Console.WriteLine(sb.ToString());
// {
//   "CPU": "Intel",
//   "PSU": "500W",
//   "Drives": [
//     "DVD read/writer"
//     /*(broken)*/,
//     "500 gigabyte hard drive",
//     "200 gigabyte hard drive"
//   ]
// }

獲取屬性的值可以用linq

using Newtonsoft.Json.Linq;

JObject o = JObject.Parse(@"{
  'CPU': 'Intel',
  'Drives': [
    'DVD read/writer',
    '500 gigabyte hard drive'
  ]
}");

string cpu = (string)o["CPU"];
// Intel

string firstDrive = (string)o["Drives"][0];
// DVD read/writer

IList<string> allDrives = o["Drives"].Select(t => (string)t).ToList();
// DVD read/writer
// 500 gigabyte hard drive

如果是數組可以用JArray

string json = @"[
  'Small',
  'Medium',
  'Large'
]";

JArray a = JArray.Parse(json);

將類轉化成Json

類與Json互相轉化，可以利用SerializeObject以及DeserializeObject。

Product product = new Product();

product.Name = "Apple";
product.ExpiryDate = new DateTime(2008, 12, 28);
product.Price = 3.99M;
product.Sizes = new string[] { "Small", "Medium", "Large" };

string output = JsonConvert.SerializeObject(product);
//{
//  "Name": "Apple",
//  "ExpiryDate": "2008-12-28T00:00:00",
//  "Price": 3.99,
//  "Sizes": [
//    "Small",
//    "Medium",
//    "Large"
//  ]
//}

Product deserializedProduct = JsonConvert.DeserializeObject<Product>(output);

如果想要更多的序列化控制方法，可以利用JsonSerializer。

Product product = new Product();
product.ExpiryDate = new DateTime(2008, 12, 28);

JsonSerializer serializer = new JsonSerializer();
serializer.Converters.Add(new JavaScriptDateTimeConverter());
serializer.NullValueHandling = NullValueHandling.Ignore;

using (StreamWriter sw = new StreamWriter(@"c:\json.txt"))
using (JsonWriter writer = new JsonTextWriter(sw))
{
    serializer.Serialize(writer, product);
    // {"ExpiryDate":new Date(1230375600000),"Price":0}
}

利用Linq查詢json

string json = @"{
    'channel': {
        'title': 'James Newton-King',
        'link': 'http://james.newtonking.com',
        'description': 'James Newton-King\'s blog.',
        'item': [
            {
                'title': 'Json.NET 1.3 + New license + Now on CodePlex',
                'description': 'Announcing the release of Json.NET 1.3, the MIT license and the source on CodePlex',
                'link': 'http://james.newtonking.com/projects/json-net.aspx',
                'categories': [
                    'Json.NET',
                    'CodePlex'
                ]
            },
            {
                'title': 'LINQ to JSON beta',
                'description': 'Announcing LINQ to JSON',
                'link': 'http://james.newtonking.com/projects/json-net.aspx',
                'categories': [
                    'Json.NET',
                    'LINQ'
                ]
            }
        ]
    }
}";

JObject rss = JObject.Parse(json);

string rssTitle = (string)rss["channel"]["title"];
// James Newton-King

string itemTitle = (string)rss["channel"]["item"][0]["title"];
// Json.NET 1.3 + New license + Now on CodePlex

JArray categories = (JArray)rss["channel"]["item"][0]["categories"];
// ["Json.NET", "CodePlex"]

IList<string> categoriesText = categories.Select(c => (string)c).ToList();
// Json.NET
// CodePlex

用SelectToken查詢json

selectToken是JToken的方法，如果查到就返回值，查不到就返回null

JObject o = JObject.Parse(@"{
  'Stores': [
    'Lambton Quay',
    'Willis Street'
  ],
  'Manufacturers': [
    {
      'Name': 'Acme Co',
      'Products': [
        {
          'Name': 'Anvil',
          'Price': 50
        }
      ]
    },
    {
      'Name': 'Contoso',
      'Products': [
        {
          'Name': 'Elbow Grease',
          'Price': 99.95
        },
        {
          'Name': 'Headlight Fluid',
          'Price': 4
        }
      ]
    }
  ]
}");

string name = (string)o.SelectToken("Manufacturers[0].Name");
// Acme Co

decimal productPrice = (decimal)o.SelectToken("Manufacturers[0].Products[0].Price");
// 50

string productName = (string)o.SelectToken("Manufacturers[1].Products[0].Name");
// Elbow Grease

利用JSONPath使用selectToken

JObject o = JObject.Parse(@"{
  'Stores': [
    'Lambton Quay',
    'Willis Street'
  ],
  'Manufacturers': [
    {
      'Name': 'Acme Co',
      'Products': [
        {
          'Name': 'Anvil',
          'Price': 50
        }
      ]
    },
    {
      'Name': 'Contoso',
      'Products': [
        {
          'Name': 'Elbow Grease',
          'Price': 99.95
        },
        {
          'Name': 'Headlight Fluid',
          'Price': 4
        }
      ]
    }
  ]
}");

// manufacturer with the name 'Acme Co'
JToken acme = o.SelectToken("$.Manufacturers[?(@.Name == 'Acme Co')]");

Console.WriteLine(acme);
// { "Name": "Acme Co", Products: [{ "Name": "Anvil", "Price": 50 }] }

// name of all products priced 50 and above
IEnumerable<JToken> pricyProducts = o.SelectTokens("$..Products[?(@.Price >= 50)].Name");

foreach (JToken item in pricyProducts)
{
    Console.WriteLine(item);
}
// Anvil
// Elbow Grease

SelectToken with Linq

JObject o = JObject.Parse(@"{
  'Stores': [
    'Lambton Quay',
    'Willis Street'
  ],
  'Manufacturers': [
    {
      'Name': 'Acme Co',
      'Products': [
        {
          'Name': 'Anvil',
          'Price': 50
        }
      ]
    },
    {
      'Name': 'Contoso',
      'Products': [
        {
          'Name': 'Elbow Grease',
          'Price': 99.95
        },
        {
          'Name': 'Headlight Fluid',
          'Price': 4
        }
      ]
    }
  ]
}");

IList<string> storeNames = o.SelectToken("Stores").Select(s => (string)s).ToList();
// Lambton Quay
// Willis Street

IList<string> firstProductNames = o["Manufacturers"].Select(m => (string)m.SelectToken("Products[1].Name")).ToList();
// null
// Headlight Fluid

decimal totalPrice = o["Manufacturers"].Sum(m => (decimal)m.SelectToken("Products[0].Price"));
// 149.95