.NET Core 处理 WebAPI JSON 返回烦人的null为空（.net面试题）

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public void ConfigureServices(IServiceCollection services)
{
 //配置Mvc + json 序列化
 services.AddMvc()
  .AddNewtonsoftJson(options =>
  {
   //数据格式首字母小写 不使用驼峰 小驼峰firstName 大驼峰 FirstName
   options.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
   //使用默认方式，不更改元数据的key的大小写
   //options.SerializerSettings.ContractResolver = new DefaultContractResolver();
   // 忽略循环引用
   options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
   // 设置时间格式
   options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
   //忽略空值 不包含属性的null序列化
   //options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
   //忽略默认值和null 1、不包含属性默认值和null
   //options.SerializerSettings.DefaultValueHandling = DefaultValueHandling.Igno
  })
}

/*包含属性的默认值与null序列化*/
{
 "Name": null,
 "Age": 0,
 "Partner": null,
 "Salary": 0.0
}
/*不包含属性的默认值序列化*/
{
 "Name": "Hello World",
 "Age": 28
}
/*不包含属性的null序列化*/
{
 "Name": "Hello World",
 "Age": 28,
 "Salary": 0.0
}

{
 "code": 0,
 "msg": "查询成功",
 "data": {
  "id": 1,
  "title": "炎炎夏日暖暖肚",
  "describe": "",
  "author": null,
  "authorId": null,
  "linkSource": null,
  "author_Picture": null,
  "content": "炎炎夏日，很多人喜欢吃些寒凉的食物解暑，可这种做法非常伤身。",
 }
}

public class NullToEmptyStringResolver : CamelCasePropertyNamesContractResolver
{
  /// <summary>
  /// 创建属性
  /// </summary>
  /// <param name="type">类型</param>
  /// <param name="memberSerialization">序列化成员</param>
  /// <returns></returns>
  protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
  {
    return type.GetProperties().Select(c =>
        {
          var jsonProperty = base.CreateProperty(c, memberSerialization);
          jsonProperty.ValueProvider = new NullToEmptyStringValueProvider(c);
          return jsonProperty;
        }).ToList();
  }
}

public class NullToEmptyStringValueProvider : IValueProvider
{
  private readonly PropertyInfo _memberInfo;
  /// <summary>
  /// 构造函数
  /// </summary>
  /// <param name="memberInfo"></param>
  public NullToEmptyStringValueProvider(PropertyInfo memberInfo)
  {
    _memberInfo = memberInfo;
  }

  /// <summary>
  /// 获取Value
  /// </summary>
  /// <param name="target"></param>
  /// <returns></returns>
  public object GetValue(object target)
  {
    var result = _memberInfo.GetValue(target);
    if (_memberInfo.PropertyType == typeof(string) && result == null)
      result = string.Empty;
    return result;
  }

  /// <summary>
  /// 设置Value
  /// </summary>
  /// <param name="target"></param>
  /// <param name="value"></param>
  public void SetValue(object target, object value)
  {
    _memberInfo.SetValue(target, value);
  }
}

//配置MVC+JSON序列化
services
  .AddMvc(options =>{options.EnableEndpointRouting = false;})
  .AddNewtonsoftJson(options =>
  {
    //使用默认方式，不更改元数据的key的大小写
    //options.SerializerSettings.ContractResolver = new DefaultContractResolver();
    //数据格式首字母小写 不使用驼峰  小驼峰firstName 大驼峰 FirstName
    //options.SerializerSettings.ContractResolver = new CamelCasePropertyNamesContractResolver();
    options.SerializerSettings.ContractResolver = new NullToEmptyStringResolver();
    // 忽略循环引用
    options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
    // 设置时间格式
    options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
    //忽略空值 不包含属性的null序列化
    //options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;
    //忽略默认值和null 1、不包含属性默认值和null
    //options.SerializerSettings.DefaultValueHandling = DefaultValueHandling.Igno
  })

{
 "code": 0,
 "msg": "查询成功！",
 "data": {
  "id": 1,
  "title": "炎炎夏日暖暖肚",
  "describe": "",
  "author": "",
  "authorId": "",
  "linkSource": "",
  "author_Picture": "",
  "source": 0,
  "content": "炎炎夏日，很多人喜欢吃些寒凉的食物解暑，可这种做法非常伤身。"
 }
}