Asp.net core 如何从控制器返回JSON null

我有以下行动：

    [Route("GetNull")]
    [HttpGet]
    public IActionResult GetNull()
    {
        object value = new { Name = "John" };
        return Ok(value);
    }

它返回序列化对象：

HTTP/1.1 200 OK
Date: Tue, 12 Jun 2018 06:13:05 GMT
Content-Type: application/json; charset=utf-8
Server: Kestrel
Content-Length: 22

{
  "name": "John"
}

如果对象设置为空，如下所示：

    [Route("GetNull")]
    [HttpGet]
    public IActionResult GetNull()
    {
        object value = null;
        return Ok(value);
    }

HTTP/1.1 204 No Content
Date: Tue, 12 Jun 2018 06:17:37 GMT
Server: Kestrel
Content-Length: 0

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Server: Kestrel
Date: Tue, 12 Jun 2018 12:36:33 GMT

我希望JSON中返回null。但是，我得到的是这样的空内容：

    [Route("GetNull")]
    [HttpGet]
    public IActionResult GetNull()
    {
        object value = null;
        return Ok(value);
    }

HTTP/1.1 204 No Content
Date: Tue, 12 Jun 2018 06:17:37 GMT
Server: Kestrel
Content-Length: 0

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Server: Kestrel
Date: Tue, 12 Jun 2018 12:36:33 GMT

我需要让控制器将null序列化为json并返回：

HTTP/1.1 200 OK
Date: Tue, 12 Jun 2018 06:13:05 GMT
Content-Type: application/json; charset=utf-8
Server: Kestrel
Content-Length: 4

null

---

ASP.NET Core有一个特定的输出格式化程序，当您尝试返回null时，它将返回

204-NoContent

响应。要允许您返回null并获得200响应，您可以删除NoContent的默认格式化程序

在

startup.cs

中：

services.AddMvc(options =>
{
    options.OutputFormatters.RemoveType<HttpNoContentOutputFormatter>();
});

您必须注意，ASP.NET将始终尝试将响应格式化为JSON，因为这是默认的响应格式。因此，响应头将如下所示：

    [Route("GetNull")]
    [HttpGet]
    public IActionResult GetNull()
    {
        object value = null;
        return Ok(value);
    }

HTTP/1.1 204 No Content
Date: Tue, 12 Jun 2018 06:17:37 GMT
Server: Kestrel
Content-Length: 0

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Server: Kestrel
Date: Tue, 12 Jun 2018 12:36:33 GMT

重要的是状态代码现在是

200

---

Microsoft文档是

为什么希望此

返回Json（null）

返回Json（值？？“null”）<代码>返回Json（空）