.NET 6 中的七个 System.Text.Json 特性

忽略循环引用

在 .NET 5 中，如果存在循环依赖, 那么序列化的时候会抛出异常, 而在 .NET 6 中, 你可以选择忽略它。

Category dotnet = new()
{Name = ".NET 6",
};
Category systemTextJson = new()
{Name = "System.Text.Json",Parent = dotnet
};
dotnet.Children.Add(systemTextJson);JsonSerializerOptions options = new()
{ReferenceHandler = ReferenceHandler.IgnoreCycles,WriteIndented = true
};string dotnetJson = JsonSerializer.Serialize(dotnet, options);
Console.WriteLine($"{dotnetJson}");public class Category
{public string Name { get; set; }public Category Parent { get; set; }public List<Category> Children { get; set; } = new();
}// 输出:
// {
//   "Name": ".NET 6",
//   "Parent": null,
//   "Children": [
//     {
//       "Name": "System.Text.Json",
//       "Parent": null,
//       "Children": []
//     }
//   ]
// }

序列化和反序列化通知

在 .NET 6 中，System.Text.Json 公开序列化和反序列化的通知。

有四个新接口可以根据您的需要进行实现：

•IJsonOnDeserialized•IJsonOnDeserializing•IJsonOnSerialized•IJsonOnSerializing

Product invalidProduct = new() { Name = "Name", Test = "Test" };
JsonSerializer.Serialize(invalidProduct);
// The InvalidOperationException is thrownstring invalidJson = "{}";
JsonSerializer.Deserialize<Product>(invalidJson);
// The InvalidOperationException is thrownclass Product : IJsonOnDeserialized, IJsonOnSerializing, IJsonOnSerialized
{public string Name { get; set; }public string Test { get; set; }public void OnSerialized(){throw new NotImplementedException();}void IJsonOnDeserialized.OnDeserialized() => Validate(); // Call after deserializationvoid IJsonOnSerializing.OnSerializing() => Validate();   // Call before serializationprivate void Validate(){if (Name is null){throw new InvalidOperationException("The 'Name' property cannot be 'null'.");}}
}

序列化支持属性排序

在 .NET 6 中, 添加了 JsonPropertyOrderAttribute 特性，允许控制属性的序列化顺序，以前，序列化顺序是由反射顺序决定的。

Product product = new()
{Id = 1,Name = "Surface Pro 7",Price = 550,Category = "Laptops"
};JsonSerializerOptions options = new() { WriteIndented = true };
string json = JsonSerializer.Serialize(product, options);
Console.WriteLine(json);class Product : A
{[JsonPropertyOrder(2)]  public string Category { get; set; }[JsonPropertyOrder(1)]  public decimal Price { get; set; }public string Name { get; set; }  [JsonPropertyOrder(-1)]  public int Id { get; set; }
}class A
{public int Test { get; set; }
}// 输出:
// {
//   "Id": 1,
//   "Name": "Surface Pro 7",
//   "Price": 550,
//   "Category": "Laptops"
// }

使用 Utf8JsonWriter 编写 JSON

.NET 6 增加了 System.Text.Json.Utf8JsonWriter，你可以方便的用它编写原始Json。

JsonWriterOptions writerOptions = new() { Indented = true, };using MemoryStream stream = new();
using Utf8JsonWriter writer = new(stream, writerOptions);writer.WriteStartObject();
writer.WriteStartArray("customJsonFormatting");
foreach (double result in new double[] { 10.2, 10 })
{writer.WriteStartObject();writer.WritePropertyName("value");writer.WriteRawValue(FormatNumberValue(result), skipInputValidation: true);writer.WriteEndObject();
}
writer.WriteEndArray();
writer.WriteEndObject();
writer.Flush();string json = Encoding.UTF8.GetString(stream.ToArray());
Console.WriteLine(json);static string FormatNumberValue(double numberValue)
{return numberValue == Convert.ToInt32(numberValue)? numberValue.ToString() + ".0": numberValue.ToString();
}// 输出:
// {
//    "customJsonFormatting": [
//      {
//        "value": 10.2
//      },
//      {
//        "value": 10.0
//      }
//  ]
// }

IAsyncEnumerable 支持

在 .NET 6 中， System.Text.Json 支持 IAsyncEnumerable。

static async IAsyncEnumerable<int> GetNumbersAsync(int n)
{for (int i = 0; i < n; i++){await Task.Delay(1000);yield return i;}
}
// Serialization using IAsyncEnumerable
JsonSerializerOptions options = new() { WriteIndented = true };
using Stream 输出Stream = Console.OpenStandard输出();
var data = new { Data = GetNumbersAsync(5) };
await JsonSerializer.SerializeAsync(输出Stream, data, options);
// 输出:
// {
//    "Data": [
//      0,
//      1,
//      2,
//      3,
//      4
//  ]
// }// Deserialization using IAsyncEnumerable
using MemoryStream memoryStream = new(Encoding.UTF8.GetBytes("[0,1,2,3,4]"));
// Wraps the UTF-8 encoded text into an IAsyncEnumerable<T> that can be used to deserialize root-level JSON arrays in a streaming manner.
await foreach (int item in JsonSerializer.DeserializeAsyncEnumerable<int>(memoryStream))
{Console.WriteLine(item);
}
// 输出:
// 0
// 1
// 2
// 3
// 4

IAsyncEnumerable 的序列化的动图。

序列化支持流

在 .NET 6 中, 序列化和反序列化支持流。

string json = "{\"Value\":\"Deserialized from stream\"}";
byte[] bytes = Encoding.UTF8.GetBytes(json);// Deserialize from stream
using MemoryStream ms = new MemoryStream(bytes);
Example desializedExample = JsonSerializer.Deserialize<Example>(ms);
Console.WriteLine(desializedExample.Value);
// 输出: Deserialized from stream// ==================================================================// Serialize to stream
JsonSerializerOptions options = new() { WriteIndented = true };
using Stream 输出Stream = Console.OpenStandard输出();
Example exampleToSerialize = new() { Value = "Serialized from stream" };
JsonSerializer.Serialize<Example>(输出Stream, exampleToSerialize, options);
// 输出:
// {
//    "Value": "Serialized from stream"
// }class Example
{public string Value { get; set; }
}

像 DOM 一样使用 JSON

.NET 6 添加了下面的新类型, 支持像操作 DOM 一样访问 Json 元素。

•JsonArray•JsonNode•JsonObject•JsonValue

// Parse a JSON object
JsonNode jNode = JsonNode.Parse("{\"Value\":\"Text\",\"Array\":[1,5,13,17,2]}");
string value = (string)jNode["Value"];
Console.WriteLine(value); // Text// or
value = jNode["Value"].GetValue<string>();
Console.WriteLine(value); // Textint arrayItem = jNode["Array"][1].GetValue<int>();
Console.WriteLine(arrayItem); // 5// or
arrayItem = jNode["Array"][1].GetValue<int>();
Console.WriteLine(arrayItem); // 5// Create a new JsonObject
var jObject = new JsonObject
{["Value"] = "Text",["Array"] = new JsonArray(1, 5, 13, 17, 2)
};
Console.WriteLine(jObject["Value"].GetValue<string>());  // Text
Console.WriteLine(jObject["Array"][1].GetValue<int>());  // 5// Converts the current instance to string in JSON format
string json = jObject.ToJsonString();
Console.WriteLine(json); // {"Value":"Text","Array":[1,5,13,17,2]}

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