使用C#对JSON进行序列化和反序列化 - C#

本文演示如何使用 System.Text.Json 命名空间向 / 从 JavaScript 对象表示法 (JSON) 进行序列化和反序列化。
本文参考：https://learn.microsoft.com/zh-cn/dotnet/standard/serialization/system-text-json/how-to?pivots=dotnet-6-0

# 命名空间

	using System.Text.Json;
	using System.Text.Json.Serialization;

# 最简单将.NET 对象编写为 JSON

Console.WriteLine(JsonSerializer.Serialize(item));

# 如何将 .NET 对象编写为 JSON（序列化）

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"}

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"}

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";
	using FileStream createStream = File.Create(fileName);
	await JsonSerializer.SerializeAsync(createStream, weatherForecast);
	await createStream.DisposeAsync();

	Console.WriteLine(File.ReadAllText(fileName));
	}
	}
	}
	// output:
	//{"Date":"2019-08-01T00:00:00-07:00","TemperatureCelsius":25,"Summary":"Hot"}

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"}

# 序列化示例

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"
	// ]
	//}

# 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%。出现这种差别的原因是字节（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);

# 如何将 JSON 读取为 .NET 对象（反序列化）

以下示例演示如何对 JSON 字符串进行反序列化：

	using System.Text.Json;

	namespace DeserializeExtra
	{
	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()
	{
	string jsonString =
	@"{
	""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""
	]
	}
	";

	WeatherForecast? weatherForecast =
	JsonSerializer.Deserialize<WeatherForecast>(jsonString);

	Console.WriteLine($"Date: {weatherForecast?.Date}");
	Console.WriteLine($"TemperatureCelsius: {weatherForecast?.TemperatureCelsius}");
	Console.WriteLine($"Summary: {weatherForecast?.Summary}");
	}
	}
	}
	// output:
	//Date: 8/1/2019 12:00:00 AM -07:00
	//TemperatureCelsius: 25
	//Summary: Hot

若要使用同步代码从文件进行反序列化，请将文件读入字符串中，如下面的示例中所示:

	using System.Text.Json;

	namespace DeserializeFromFile
	{
	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()
	{
	string fileName = "WeatherForecast.json";
	string jsonString = File.ReadAllText(fileName);
	WeatherForecast weatherForecast = JsonSerializer.Deserialize<WeatherForecast>(jsonString)!;

	Console.WriteLine($"Date: {weatherForecast.Date}");
	Console.WriteLine($"TemperatureCelsius: {weatherForecast.TemperatureCelsius}");
	Console.WriteLine($"Summary: {weatherForecast.Summary}");
	}
	}
	}
	// output:
	//Date: 8/1/2019 12:00:00 AM -07:00
	//TemperatureCelsius: 25
	//Summary: Hot

若要使用异步代码从文件进行反序列化，请调用 DeserializeAsync 方法：

	using System.Text.Json;

	namespace DeserializeFromFileAsync
	{
	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()
	{
	string fileName = "WeatherForecast.json";
	using FileStream openStream = File.OpenRead(fileName);
	WeatherForecast? weatherForecast =
	await JsonSerializer.DeserializeAsync<WeatherForecast>(openStream);

	Console.WriteLine($"Date: {weatherForecast?.Date}");
	Console.WriteLine($"TemperatureCelsius: {weatherForecast?.TemperatureCelsius}");
	Console.WriteLine($"Summary: {weatherForecast?.Summary}");
	}
	}
	}
	// output:
	//Date: 8/1/2019 12:00:00 AM -07:00
	//TemperatureCelsius: 25
	//Summary: Hot

# 从 UTF-8 进行反序列化

若要从 UTF-8 进行反序列化，请调用采用 ReadOnlySpan<byte> 或 Utf8JsonReader 的 JsonSerializer.Deserialize 重载，如下面的示例中所示。这些示例假设 JSON 处于名为 jsonUtf8Bytes 的字节数组中。

	var readOnlySpan = new ReadOnlySpan<byte>(jsonUtf8Bytes);
	WeatherForecast deserializedWeatherForecast =
	JsonSerializer.Deserialize<WeatherForecast>(readOnlySpan)!;

	var utf8Reader = new Utf8JsonReader(jsonUtf8Bytes);
	WeatherForecast deserializedWeatherForecast =
	JsonSerializer.Deserialize<WeatherForecast>(ref utf8Reader)!;

# 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：

p 24

	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"
	//}