1、前言

在Web开发中，JSON数据可以说是无处不在。由于具有轻量、易读等优点，JSON已经成为当前主流的数据传输格式。在ASP.NET Core 3.0之前，大多数项目都会使用Newtonsoft.Json组件来实现JSON的序列化和反序列化操作，而从ASP.NET Core 3.1开始，微软提供的System.Text.Json已经相当出色，其效率相比前者可以说是有过之而无不及，下面就来介绍一下它的使用方法。

2、引入System.Text.Json

新建一个Web API项目，使用NuGet引入如下组件：

System.Text.Json

新建一个实体类Person，代码如下：

using System;namespace App
{public class Person{public int Id { get; set; }public string PersonName { get; set; }public string PersonGender { get; set; }public DateTime? BirthOfDate { get; set; }}
}

新建一个控制器PersonController，添加一个Get方法，代码如下：

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list);}}
}

运行结果如下所示：

[{"id":1,"personName":"\u5F20\u4E09","personGender":"\u7537","birthOfDate":"2000-01-01T00:00:00"},{"id":1,"personName":"\u674E\u56DB","personGender":"\u5973","birthOfDate":"2000-02-02T00:00:00"},{"id":1,"personName":"\u738B\u4E94","personGender":"\u7537","birthOfDate":"2000-03-03T00:00:00"}]

上面的代码实现了一个简单的JSON序列化操作，但里面的问题也有很多，比如中文乱码、时间格式等等，下面就来说一说如何在System.Text.Json中去设置它们。

3、序列化操作

3.1、JSON数据编码

上面的运行结果显示中文乱码，我们可以使用JsonSerializerOptions中的Encoder来指定编码格式，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Unicode;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list, new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping});}}
}

运行结果如下所示，可以发现中文编码正确。

[{"Id":1,"PersonName":"张三","PersonGender":"男","BirthOfDate":"2000-01-01T00:00:00"},{"Id":2,"PersonName":"李四","PersonGender":"女","BirthOfDate":"2000-02-02T00:00:00"},{"Id":3,"PersonName":"王五","PersonGender":"男","BirthOfDate":"2000-03-03T00:00:00"}]

3.2、JSON文本格式化

默认输出的JSON文本是未经格式化的，如果你希望JSON看起来清楚一些，可以设置WriteIndented属性值，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Unicode;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list, new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,WriteIndented = true});}}
}

运行结果如下所示，可以发现JSON文本已经被格式化了。

[{"Id": 1,"PersonName": "张三","PersonGender": "男","BirthOfDate": "2000-01-01T00:00:00"},{"Id": 2,"PersonName": "李四","PersonGender": "女","BirthOfDate": "2000-02-02T00:00:00"},{"Id": 3,"PersonName": "王五","PersonGender": "男","BirthOfDate": "2000-03-03T00:00:00"}
]

3.3、JSON字段命名格式

上面的输出结果遵循的是首字母大写的帕斯卡命名格式，如果希望输出结果采用驼峰式进行命名，则可以对PropertyNamingPolicy进行设置，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Unicode;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list, new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,WriteIndented = true,PropertyNamingPolicy = JsonNamingPolicy.CamelCase});}}
}

运行结果如下所示，可以发现JSON文本采用的是驼峰式命名。

[{"id": 1,"personName": "张三","personGender": "男","birthOfDate": "2000-01-01T00:00:00"},{"id": 2,"personName": "李四","personGender": "女","birthOfDate": "2000-02-02T00:00:00"},{"id": 3,"personName": "王五","personGender": "男","birthOfDate": "2000-03-03T00:00:00"}
]

3.4、忽略JSON中的null值

在序列化时，如果对象的属性值为null，则结果中也会显示为null。如果希望忽略null值，则可以对DefaultIgnoreCondition进行设置，代码如下：

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.Unicode;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = null },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = null },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = null }};return new JsonResult(list, new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,WriteIndented = true,PropertyNamingPolicy = JsonNamingPolicy.CamelCase,DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull});}}
}

运行结果如下所示，可以发现BirthOfDate字段的值被忽略了。

[{"id": 1,"personName": "张三","personGender": "男"},{"id": 2,"personName": "李四","personGender": "女"},{"id": 3,"personName": "王五","personGender": "男"}
]

3.5.、JSON忽略只读字段

一般来说，由于只读字段无法进行反序列化操作，因此在序列化时可以考虑忽略。现在对Person代码进行修改，添加一个只读字段Info，代码如下：

using System;namespace App
{public class Person{public int Id { get; set; }public string PersonName { get; set; }public string PersonGender { get; set; }public DateTime? BirthOfDate { get; set; }public string Info{get { return $"姓名：{PersonName}，性别：{PersonGender}，出生日期：{BirthOfDate}"; }}}
}

我们可以对JsonSerializerOptions中的IgnoreReadOnlyProperties字段进行设置，从而忽略只读字段，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Json.Serialization;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list, new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,WriteIndented = true,PropertyNamingPolicy = JsonNamingPolicy.CamelCase,DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,IgnoreReadOnlyProperties = true});}}
}

运行结果如下所示，可以发现Info字段并没有被序列化。

[{"id": 1,"personName": "张三","personGender": "男","birthOfDate": "2000-01-01T00:00:00"},{"id": 2,"personName": "李四","personGender": "女","birthOfDate": "2000-02-02T00:00:00"},{"id": 3,"personName": "王五","personGender": "男","birthOfDate": "2000-03-03T00:00:00"}
]

3.6、JSON中的时间格式

在上面的代码中，时间字段BirthOfDate的序列化结果有一些问题，如何把它序列化成我们熟悉的时间格式呢？首先定义一个类DateTimeJsonConverter，该类继承JsonConverter，代码如下：

using System;
using System.Text.Json;
using System.Text.Json.Serialization;namespace App
{public class DateTimeJsonConverter : JsonConverter{public override DateTime Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options){if (reader.TokenType == JsonTokenType.String){if (DateTime.TryParse(reader.GetString(), out DateTime dateTime)){return dateTime;}}return reader.GetDateTime();}public override void Write(Utf8JsonWriter writer, DateTime value, JsonSerializerOptions options){writer.WriteStringValue(value.ToString("yyyy年MM月dd日 HH时mm分ss秒"));}}
}

然后在JsonSerializerOptions中的Converters集合中加入它即可，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.Unicode;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1, 0, 0, 0) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};JsonSerializerOptions options = new JsonSerializerOptions{Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping,WriteIndented = true,PropertyNamingPolicy = JsonNamingPolicy.CamelCase,DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull};options.Converters.Add(new DateTimeJsonConverter());return new JsonResult(list, options);}}
}

运行结果如下所示，可以发现BirthOfDate字段的值已经被格式化。

[{"id": 1,"personName": "张三","personGender": "男","birthOfDate": "2000年01月01日 00时00分00秒"},{"id": 2,"personName": "李四","personGender": "女","birthOfDate": "2000年02月02日 00时00分00秒"},{"id": 3,"personName": "王五","personGender": "男","birthOfDate": "2000年03月03日 00时00分00秒"}
]

4、反序列化操作

4.1、常规操作

JSON的反序列化操作比较简单，只需要调用Deserialize即可。代码如下：

using Microsoft.AspNetCore.Mvc;
using System.Text.Json;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public ActionResult Get(){string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\"}";Person person = JsonSerializer.Deserialize(json);return $"姓名：{person.PersonName}\n性别：{person.PersonGender}\n出生日期：{person.BirthOfDate}";}}
}

运行结果如下所示：

姓名：张三
性别：男
出生日期：2000/1/1 0:00:00

4.2、特殊情况的处理

在进行反序列化操作时，有一种情况需要特别注意，那就是属性值末尾存在逗号的情况。在JavaScript中，下面的代码是允许的，即：在BirthOfDate的属性值后面允许添加一个逗号：

{"Id": 1,"PersonName": "张三","PersonGender": "男","BirthOfDate": "2000-01-01T00:00:00",
}

但这种情况会导致反序列化报错，代码如下：

using Microsoft.AspNetCore.Mvc;
using System.Text.Json;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public ActionResult Get(){string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\",}";Person person = JsonSerializer.Deserialize(json);return $"姓名：{person.PersonName}\n性别：{person.PersonGender}\n出生日期：{person.BirthOfDate}";}}
}

运行结果如下图所示：

如果要允许这种末尾添加逗号的情况，需要设置JsonSerializerOptions的AllowTrailingCommas属性，代码如下：

using Microsoft.AspNetCore.Mvc;
using System.Text.Json;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public ActionResult Get(){string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\",}";Person person = JsonSerializer.Deserialize(json, new JsonSerializerOptions{AllowTrailingCommas = true});return $"姓名：{person.PersonName}\n性别：{person.PersonGender}\n出生日期：{person.BirthOfDate}";}}
}

运行结果如下所示：

姓名：张三
性别：男
出生日期：2000/1/1 0:00:00

5、全局配置JSON

上面的代码是在单个方法中设置JSON操作属性，如果当前存在很多方法，则必然会导致代码臃肿。我们可以在全局对JSON进行配置，代码如下：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System.Text.Encodings.Web;
using System.Text.Json;
using System.Text.Json.Serialization;namespace App
{public class Startup{public Startup(IConfiguration configuration){Configuration = configuration;}public IConfiguration Configuration { get; }// This method gets called by the runtime. Use this method to add services to the container.public void ConfigureServices(IServiceCollection services){services.AddControllers().AddJsonOptions(options =>{// 设置编码格式options.JsonSerializerOptions.Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping;// 是否格式化文本options.JsonSerializerOptions.WriteIndented = true;// 添加时间格式化转换器options.JsonSerializerOptions.Converters.Add(new DateTimeJsonConverter());// 字段采用驼峰式命名options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;// 忽略null值options.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;// 忽略只读字段options.JsonSerializerOptions.IgnoreReadOnlyProperties = true;// 允许属性值末尾存在逗号options.JsonSerializerOptions.AllowTrailingCommas = true;// 处理循环引用类型options.JsonSerializerOptions.ReferenceHandler = ReferenceHandler.IgnoreCycles;});}// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.public void Configure(IApplicationBuilder app, IWebHostEnvironment env){if (env.IsDevelopment()){app.UseDeveloperExceptionPage();}app.UseHttpsRedirection();app.UseRouting();app.UseAuthorization();app.UseEndpoints(endpoints =>{endpoints.MapControllers();});}}
}

在全局进行配置后，Controller中的方法就不需要单独配置了，代码如下：

using Microsoft.AspNetCore.Mvc;
using System;
using System.Collections.Generic;namespace App.Controllers
{[Route("api/[controller]/[action]")][ApiController]public class PersonController : ControllerBase{[HttpGet]public JsonResult Get(){List list = new List{new Person { Id = 1, PersonName = "张三", PersonGender = "男", BirthOfDate = new DateTime(2000, 1, 1, 0, 0, 0) },new Person { Id = 2, PersonName = "李四", PersonGender = "女", BirthOfDate = new DateTime(2000, 2, 2) },new Person { Id = 3, PersonName = "王五", PersonGender = "男", BirthOfDate = new DateTime(2000, 3, 3) }};return new JsonResult(list);}}
}

运行结果如下所示：

[{"id": 1,"personName": "张三","personGender": "男","birthOfDate": "2000年01月01日 00时00分00秒"},{"id": 2,"personName": "李四","personGender": "女","birthOfDate": "2000年02月02日 00时00分00秒"},{"id": 3,"personName": "王五","personGender": "男","birthOfDate": "2000年03月03日 00时00分00秒"}
]

6、结语

本文简单介绍了ASP.NET Core中关于JSON序列化和反序列化操作，主要通过System.Text.Json来实现。如果你觉得微软提供的JSON序列化工具不好用，那也可以使用Newtonsoft.Json，我也会在下一篇博客中介绍关于Newtonsoft.Json的使用方法。