ASP.NET Core 3.1系列（29）——System.Text.Json实现JSON的序列化和反序列化

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<Person> list = new List<Person>
            {
                new Person { Id = 1, PersonName = "张三", PersonGender = "男", PersonAge = 30 },
                new Person { Id = 2, PersonName = "李四", PersonGender = "女", PersonAge = 31 },
                new Person { Id = 3, PersonName = "王五", PersonGender = "男", PersonAge = 32 }
            };
            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<Person> list = new List<Person>
            {
                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<Person> list = new List<Person>
            {
                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<Person> list = new List<Person>
            {
                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<Person> list = new List<Person>
            {
                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<Person> list = new List<Person>
            {
                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<DateTime>代码如下

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

namespace App
{
    public class DateTimeJsonConverter : JsonConverter<DateTime>
    {
        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<Person> list = new List<Person>
            {
                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<string> Get()
        {
            string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\"}";
            Person person = JsonSerializer.Deserialize<Person>(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<string> Get()
        {
            string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\",}";
            Person person = JsonSerializer.Deserialize<Person>(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<string> Get()
        {
            string json = "{\"Id\":1,\"PersonName\":\"张三\",\"PersonGender\":\"男\",\"BirthOfDate\":\"2000-01-01T00:00:00\",}";
            Person person = JsonSerializer.Deserialize<Person>(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<Person> list = new List<Person>
            {
                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。