如何使用 System.Text.Json 允許某種無效的 JSON

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在本文中，您會了解如何在 JSON 中允許註解、後置逗號和引號數字，以及如何將數字寫入為字串。

允許註解和後置逗號

JSON 中預設不允許註解和後置逗號。 若要在 JSON 中允許註解，請將 JsonSerializerOptions.ReadCommentHandling 屬性設定為 JsonCommentHandling.Skip。 若要允許後置逗號，請將 JsonSerializerOptions.AllowTrailingCommas 屬性設定為 true。 下列範例示範如何允許這兩者：

var options = new JsonSerializerOptions
{
    ReadCommentHandling = JsonCommentHandling.Skip,
    AllowTrailingCommas = true,
};
WeatherForecast weatherForecast = JsonSerializer.Deserialize<WeatherForecast>(
    jsonString,
    options
    )!;

Dim options As JsonSerializerOptions = New JsonSerializerOptions With {
    .ReadCommentHandling = JsonCommentHandling.Skip,
    .AllowTrailingCommas = True
}
Dim weatherForecast1 = JsonSerializer.Deserialize(Of WeatherForecast)(jsonString, options)

下列是具有註解和後置逗號的範例 JSON：

{
  "Date": "2019-08-01T00:00:00-07:00",
  "TemperatureCelsius": 25, // Fahrenheit 77
  "Summary": "Hot", /* Zharko */
  // Comments on
  /* separate lines */
}

允許或寫入引號中的數字

部分序列化程式會將數字編碼為 JSON 字串 (以引號括住)。

例如：

{
    "DegreesCelsius": "23"
}

而非：

{
    "DegreesCelsius": 23
}

若要將引號中的數字序列化，或接受整個輸入物件圖的引號中數字，請設定 JsonSerializerOptions.NumberHandling，如下列範例所示：

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

namespace QuotedNumbers
{
    public class Forecast
    {
        public DateTime Date { get; init; }
        public int TemperatureC { get; set; }
        public string? Summary { get; set; }
    };

    public class Program
    {
        public static void Main()
        {
            Forecast forecast = new()
            {
                Date = DateTime.Now,
                TemperatureC = 40,
                Summary = "Hot"
            };

            JsonSerializerOptions options = new()
            {
                NumberHandling =
                    JsonNumberHandling.AllowReadingFromString |
                    JsonNumberHandling.WriteAsString,
                WriteIndented = true
            };

            string forecastJson =
                JsonSerializer.Serialize<Forecast>(forecast, options);

            Console.WriteLine($"Output JSON:\n{forecastJson}");

            Forecast forecastDeserialized =
                JsonSerializer.Deserialize<Forecast>(forecastJson, options)!;

            Console.WriteLine($"Date: {forecastDeserialized.Date}");
            Console.WriteLine($"TemperatureC: {forecastDeserialized.TemperatureC}");
            Console.WriteLine($"Summary: {forecastDeserialized.Summary}");
        }
    }
}

// Produces output like the following example:
//
//Output JSON:
//{
//  "Date": "2020-10-23T12:27:06.4017385-07:00",
//  "TemperatureC": "40",
//  "Summary": "Hot"
//}
//Date: 10/23/2020 12:27:06 PM
//TemperatureC: 40
//Summary: Hot

Imports System.Text.Json
Imports System.Text.Json.Serialization

Namespace QuotedNumbers

    Public Class Forecast
        Public Property [Date] As Date
        Public Property TemperatureC As Integer
        Public Property Summary As String
    End Class

    Public NotInheritable Class Program

        Public Shared Sub Main()
            Dim forecast1 As New Forecast() With {
                .[Date] = Date.Now,
                .TemperatureC = 40,
                .Summary = "Hot"
                }

            Dim options As New JsonSerializerOptions() With {
                .NumberHandling = JsonNumberHandling.AllowReadingFromString Or
                        JsonNumberHandling.WriteAsString,
                .WriteIndented = True
                }

            Dim forecastJson As String = JsonSerializer.Serialize(forecast1, options)

            Console.WriteLine($"Output JSON:{forecastJson}")

            Dim forecastDeserialized As Forecast = JsonSerializer.Deserialize(Of Forecast)(forecastJson, options)

            Console.WriteLine($"Date: {forecastDeserialized.[Date]}")
            Console.WriteLine($"TemperatureC: {forecastDeserialized.TemperatureC}")
            Console.WriteLine($"Summary: {forecastDeserialized.Summary}")
        End Sub

    End Class

End Namespace

' Produces output like the following example:
'
'Output JSON:
'{
'  "Date": "2020-10-23T12:27:06.4017385-07:00",
'  "TemperatureC": "40",
'  "Summary": "Hot"
'}
'Date: 10/23/2020 12:27:06 PM
'TemperatureC: 40
'Summary: Hot

因為 ASP.NET Core 會指定 Web 預設選項，所以在透過 ASP.NET Core 間接使用 System.Text.Json 時，會在還原序列化時允許引號數字。

若要允許或寫入特定屬性、欄位或型別的引號數字，請使用 [JsonNumberHandling] 屬性。

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