[Route("api/people")]
public class PeopleController : Controller
{
 [HttpPost]
 [Route("")]
 public List<Person> Add([FromBody]List<Person> people)
 {
 return people;
 }
}

[{
 firstName: 'Mike',
 lastName: 'Li'
}, {
 firstName: 'Stephie',
 lastName: 'Wang',
 schoolName: 'No.15 Middle School'
}, {
 firstName: 'Jacky',
 lastName: 'Chen',
 hospitalName: 'Center Hospital'
}]

[
 {
 "FirstName": "Mike",
 "LastName": "Li"
 },
 {
 "FirstName": "Stephie",
 "LastName": "Wang"
 },
 {
 "FirstName": "Jacky",
 "LastName": "Chen"
 }
]

public abstract class JsonCreationConverter<T> : JsonConverter
{
 public override bool CanWrite
 {
 get
 {
  return false;
 }
 }

 protected abstract T Create(Type objectType, JObject jObject);

 public override bool CanConvert(Type objectType)
 {
 return typeof(T).IsAssignableFrom(objectType);
 }


 public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
 {
 if (reader == null) throw new ArgumentNullException("reader");
 if (serializer == null) throw new ArgumentNullException("serializer");
 if (reader.TokenType == JsonToken.Null)
  return null;

 JObject jObject = JObject.Load(reader);
 T target = Create(objectType, jObject);
 serializer.Populate(jObject.CreateReader(), target);
 return target;
 }

 public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
 {
 throw new NotImplementedException();
 }
}

public class PersonJsonConverter : JsonCreationConverter<Person>
{
 protected override Person Create(Type objectType, JObject jObject)
 {
 if (jObject == null) throw new ArgumentNullException("jObject");

 if (jObject["schoolName"] != null)
 {
  return new Student();
 }
 else if (jObject["hospitalName"] != null)
 {
  return new Doctor();
 }
 else
 {
  return new Person();
 }
 }
}

[JsonConverter(typeof(PersonJsonConverter))]
public class Person
{
 public string FirstName { get; set; }

 public string LastName { get; set; }
}

[
 {
  "FirstName": "Mike",
  "LastName": "Li"
 },
 {
  "SchoolName": "No.15 Middle School",
  "FirstName": "Stephie",
  "LastName": "Wang"
 },
 {
  "HospitalName": "Center Hospital",
  "FirstName": "Jacky",
  "LastName": "Chen"
 }
]

public class MvcCoreMvcOptionsSetup : IConfigureOptions<MvcOptions>
{
 private readonly IHttpRequestStreamReaderFactory _readerFactory;
 private readonly ILoggerFactory _loggerFactory;

 ......
  
 public void Configure(MvcOptions options)
 {
  options.ModelBinderProviders.Add(new BinderTypeModelBinderProvider());
  options.ModelBinderProviders.Add(new ServicesModelBinderProvider());
  options.ModelBinderProviders.Add(new BodyModelBinderProvider(options.InputFormatters, _readerFactory, _loggerFactory, options));
  ......
 }

 ......
 
}

public async Task BindModelAsync(ModelBindingContext bindingContext)
{
 if (bindingContext == null)
 {
  throw new ArgumentNullException(nameof(bindingContext));
 }

  ….

 var formatter = (IInputFormatter)null;
 for (var i = 0; i < _formatters.Count; i++)
 {
   if (_formatters[i].CanRead(formatterContext))
  {
   formatter = _formatters[i];
   _logger"htmlcode">

public override async Task<InputFormatterResult> ReadRequestBodyAsync(
   InputFormatterContext context,
   Encoding encoding)
{
 ......

 using (var streamReader = context.ReaderFactory(request.Body, encoding))
 {
  using (var jsonReader = new JsonTextReader(streamReader))
  {
   …

   object model;
   try
   {
    model = jsonSerializer.Deserialize(jsonReader, type);
   }
   finally
   {
    jsonSerializer.Error -= ErrorHandler;
    ReleaseJsonSerializer(jsonSerializer);
   }

   …
  }
 }
}


JsonInputFormatter类中的ReadRequestBodyAsync方法负责数据绑定, 在该方法中使用了Json.NET的JsonSerializer类的Deserialize方法来进行反序列化， 这说明Mvc Core的底层是直接使用Json.NET来操作Json的。
JsonSerializer类的部分关键代码


public object Deserialize(JsonReader reader, Type objectType)
{
 return DeserializeInternal(reader, objectType);
}

internal virtual object DeserializeInternal(JsonReader reader, Type objectType)
{
 ……

 JsonSerializerInternalReader serializerReader = new JsonSerializerInternalReader(this);
 object value = serializerReader.Deserialize(traceJsonReader "htmlcode">

public object Deserialize(JsonReader reader, Type objectType, bool checkAdditionalContent)
{
 …

 JsonConverter converter = GetConverter(contract, null, null, null);

 if (reader.TokenType == JsonToken.None && !reader.ReadForType(contract, converter != null))
 {
  ......

  object deserializedValue;

  if (converter != null && converter.CanRead)
  {
   deserializedValue = DeserializeConvertable(converter, reader, objectType, null);
  }
  else
  {
   deserializedValue = CreateValueInternal(reader, objectType, contract, null, null, null, null);
  }
  }
}


JsonSerializerInternalReader类里面的Deserialize方法会尝试根据当前请求参数的类型，去查找并实例化一个合适的JsonConverter。 如果查找到匹配的Converter, 就使用该Converter进行实际的反序列化数据绑定操作。在当前例子中由于api的参数类型是Person，所以它会匹配到PersonJsonConverter, 这就是为什么我们通过添加PersonJsonConverter就完成了多态数据绑定的功能。
附源代码
总结
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