如何将 .NET 对象编写为 JSON(序列化)
本文演示如何使用 System.Text.Json 命名空间以序列化为 JavaScript 对象表示法 (JSON)。 如果要从 Newtonsoft.Json
移植现有代码,请参阅Newtonsoft.Json
。
若要将 JSON 编写为字符串或文件,请调用 JsonSerializer.Serialize 方法。
下面的示例将 JSON 创建为字符串:
using System.Text.Json;
namespace SerializeBasic
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static void Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot"
};
string jsonString = JsonSerializer.Serialize(weatherForecast);
Console.WriteLine(jsonString);
}
}
}
// output:
//{"Date":"2019-08-01T00:00:00-07:00","TemperatureCelsius":25,"Summary":"Hot"}
Dim jsonString As String
默认情况下,JSON 输出会缩小(将删除空格、缩进和换行符)。
下面的示例使用同步代码创建 JSON 文件:
using System.Text.Json;
namespace SerializeToFile
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static void Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot"
};
string fileName = "WeatherForecast.json";
string jsonString = JsonSerializer.Serialize(weatherForecast);
File.WriteAllText(fileName, jsonString);
Console.WriteLine(File.ReadAllText(fileName));
}
}
}
// output:
//{"Date":"2019-08-01T00:00:00-07:00","TemperatureCelsius":25,"Summary":"Hot"}
jsonString = JsonSerializer.Serialize(weatherForecast1)
File.WriteAllText(fileName, jsonString)
下面的示例使用异步代码创建 JSON 文件:
using System.Text.Json;
namespace SerializeToFileAsync
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static async Task Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot"
};
string fileName = "WeatherForecast.json";
await using FileStream createStream = File.Create(fileName);
await JsonSerializer.SerializeAsync(createStream, weatherForecast);
Console.WriteLine(File.ReadAllText(fileName));
}
}
}
// output:
//{"Date":"2019-08-01T00:00:00-07:00","TemperatureCelsius":25,"Summary":"Hot"}
Dim createStream As FileStream = File.Create(fileName)
Await JsonSerializer.SerializeAsync(createStream, weatherForecast1)
前面的示例对要序列化的类型使用类型推理。 Serialize()
的重载采用泛型类型参数:
using System.Text.Json;
namespace SerializeWithGenericParameter
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static void Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot"
};
string jsonString = JsonSerializer.Serialize<WeatherForecast>(weatherForecast);
Console.WriteLine(jsonString);
}
}
}
// output:
//{"Date":"2019-08-01T00:00:00-07:00","TemperatureCelsius":25,"Summary":"Hot"}
jsonString = JsonSerializer.Serialize(Of WeatherForecastWithPOCOs)(weatherForecast)
序列化行为
- 默认情况下,所有公共属性都会序列化。 可以指定要忽略的属性。 还可包括专用成员。
- 默认编码器会转义非 ASCII 字符、ASCII 范围内的 HTML 敏感字符以及根据 RFC 8259 JSON 规范必须进行转义的字符。
- 默认情况下,JSON 会缩小。 可以对 JSON 进行优质打印。
- 默认情况下,JSON 名称的大小写与 .NET 名称匹配。 可以自定义 JSON 名称大小写。
- 默认情况下,检测到循环引用并引发异常。 可以保留引用并处理循环引用。
- 默认情况下忽略字段。 可以包含字段。
当你在 ASP.NET Core 应用中间接使用 System.Text.Json 时,某些默认行为会有所不同。 有关详细信息,请参阅 JsonSerializerOptions 的 Web 默认值。
支持的类型包括:
映射到 JavaScript 基元的 .NET 基元,如数值类型、字符串和布尔。
用户定义的普通旧 CLR 对象 (POCO)。
一维和交错数组 (
T[][]
)。来自以下命名空间的集合和字典:
- System.Collections
- System.Collections.Generic
- System.Collections.Immutable
- System.Collections.Concurrent
- System.Collections.Specialized
- System.Collections.ObjectModel
有关详细信息,请参阅 System.Text.Json 中支持的集合类型。
可以实现自定义转换器以处理其他类型或提供内置转换器不支持的功能。
以下示例演示了如何序列化包含集合属性和用户定义类型的类:
using System.Text.Json;
namespace SerializeExtra
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
public string? SummaryField;
public IList<DateTimeOffset>? DatesAvailable { get; set; }
public Dictionary<string, HighLowTemps>? TemperatureRanges { get; set; }
public string[]? SummaryWords { get; set; }
}
public class HighLowTemps
{
public int High { get; set; }
public int Low { get; set; }
}
public class Program
{
public static void Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot",
SummaryField = "Hot",
DatesAvailable = new List<DateTimeOffset>()
{ DateTime.Parse("2019-08-01"), DateTime.Parse("2019-08-02") },
TemperatureRanges = new Dictionary<string, HighLowTemps>
{
["Cold"] = new HighLowTemps { High = 20, Low = -10 },
["Hot"] = new HighLowTemps { High = 60 , Low = 20 }
},
SummaryWords = new[] { "Cool", "Windy", "Humid" }
};
var options = new JsonSerializerOptions { WriteIndented = true };
string jsonString = JsonSerializer.Serialize(weatherForecast, options);
Console.WriteLine(jsonString);
}
}
}
// output:
//{
// "Date": "2019-08-01T00:00:00-07:00",
// "TemperatureCelsius": 25,
// "Summary": "Hot",
// "DatesAvailable": [
// "2019-08-01T00:00:00-07:00",
// "2019-08-02T00:00:00-07:00"
// ],
// "TemperatureRanges": {
// "Cold": {
// "High": 20,
// "Low": -10
// },
// "Hot": {
// "High": 60,
// "Low": 20
// }
// },
// "SummaryWords": [
// "Cool",
// "Windy",
// "Humid"
// ]
//}
Public Class WeatherForecastWithPOCOs
Public Property [Date] As DateTimeOffset
Public Property TemperatureCelsius As Integer
Public Property Summary As String
Public SummaryField As String
Public Property DatesAvailable As IList(Of DateTimeOffset)
Public Property TemperatureRanges As Dictionary(Of String, HighLowTemps)
Public Property SummaryWords As String()
End Class
Public Class HighLowTemps
Public Property High As Integer
Public Property Low As Integer
End Class
' serialization output formatted (pretty-printed with whitespace and indentation):
' {
' "Date": "2019-08-01T00:00:00-07:00",
' "TemperatureCelsius": 25,
' "Summary": "Hot",
' "DatesAvailable": [
' "2019-08-01T00:00:00-07:00",
' "2019-08-02T00:00:00-07:00"
' ],
' "TemperatureRanges": {
' "Cold": {
' "High": 20,
' "Low": -10
' },
' "Hot": {
' "High": 60,
' "Low": 20
' }
' },
' "SummaryWords": [
' "Cool",
' "Windy",
' "Humid"
' ]
' }
序列化为 UTF-8
序列化为 UTF-8 字节数组比使用基于字符串的方法大约快 5-10%。 这些因为字节(作为 UTF-8)不需要转换为字符串 (UTF-16)。
若要序列化为 UTF-8 字节数组,请调用 JsonSerializer.SerializeToUtf8Bytes 方法:
byte[] jsonUtf8Bytes =JsonSerializer.SerializeToUtf8Bytes(weatherForecast);
Dim jsonUtf8Bytes As Byte()
Dim options As JsonSerializerOptions = New JsonSerializerOptions With {
.WriteIndented = True
}
jsonUtf8Bytes = JsonSerializer.SerializeToUtf8Bytes(weatherForecast1, options)
还有一个采用 Utf8JsonWriter 的 Serialize 重载可用。
序列化为格式化 JSON
若要对 JSON 输出进行优质打印,请将 JsonSerializerOptions.WriteIndented 设置为 true
:
using System.Text.Json;
namespace SerializeWriteIndented
{
public class WeatherForecast
{
public DateTimeOffset Date { get; set; }
public int TemperatureCelsius { get; set; }
public string? Summary { get; set; }
}
public class Program
{
public static void Main()
{
var weatherForecast = new WeatherForecast
{
Date = DateTime.Parse("2019-08-01"),
TemperatureCelsius = 25,
Summary = "Hot"
};
var options = new JsonSerializerOptions { WriteIndented = true };
string jsonString = JsonSerializer.Serialize(weatherForecast, options);
Console.WriteLine(jsonString);
}
}
}
// output:
//{
// "Date": "2019-08-01T00:00:00-07:00",
// "TemperatureCelsius": 25,
// "Summary": "Hot"
//}
Dim options As JsonSerializerOptions = New JsonSerializerOptions With {
.WriteIndented = True
}
jsonString = JsonSerializer.Serialize(weatherForecast, options)
提示
如果你通过相同的选项重复使用 JsonSerializerOptions
,则请勿在每次使用时都创建新的 JsonSerializerOptions
实例。 对每个调用重复使用同一实例。 有关详细信息,请参阅重用 JsonSerializerOptions 实例。