根据RFC7231 -第59页(https://www.rfc-editor.org/rfc/rfc7231#page-59) 404状态码响应的定义是:

6.5.4. 404 Not Found The 404 (Not Found) status code indicates that the origin server did not find a current representation for the target resource or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is temporary or permanent; the 410 (Gone) status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent. A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [RFC7234]).

而引起质疑的主要是上述语境中对资源的定义。 根据同一个RFC(7231)， resource的定义是:

Resources: The target of an HTTP request is called a "resource". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described in Section 2.7 of [RFC7230]. When a client constructs an HTTP/1.1 request message, it sends the target URI in one of various forms, as defined in (Section 5.3 of [RFC7230]). When a request is received, the server reconstructs an effective request URI for the target resource (Section 5.5 of [RFC7230]). One design goal of HTTP is to separate resource identification from request semantics, which is made possible by vesting the request semantics in the request method (Section 4) and a few request-modifying header fields (Section 5). If there is a conflict between the method semantics and any semantic implied by the URI itself, as described in Section 4.2.1, the method semantics take precedence.

所以在我的理解中，404状态代码不应该用于成功的GET请求，结果为空。(例如:一个没有特定过滤器结果的列表)

使用公共枚举对响应内容进行编码，以允许客户端打开它并相应地派生逻辑。我不知道你的客户如何区分“数据未找到”404和“网络资源未找到”404之间的区别?您不希望有人浏览到userZ/9，并让客户端怀疑请求是否有效，但没有返回数据。

在这个场景中，Ruby on Rails响应404 Not Found。

客户端请求不存在的资源。因此，404 Not Found更合适。

Edit

我发现，在这种情况下，许多开发人员不喜欢找不到404。

如果您不想使用404，我认为，您可以使用以下两个响应代码中的任何一个:

200好了 204无内容

如果你使用200 OK:响应体应该是空json:[]或{}

如果你使用204 OK:响应体应该为空。

为了总结或简化，

2xx:可选数据:格式良好的URI: Criteria不是URI的一部分:如果Criteria是可选的，可以在@RequestBody和@RequestParam中指定，应该导致2xx。例如:按名称/状态过滤

标准是URI的一部分:如果标准是强制性的，只能在@PathVariable中指定，那么它应该导致4xx。例如:按唯一id查找。

对于所问的情况: "users/9"将是4xx(可能是404) 但是对于“用户”呢?Name =superman”应该是2xx(可能是204)

根据RFC7231 -第59页(https://www.rfc-editor.org/rfc/rfc7231#page-59) 404状态码响应的定义是:

6.5.4. 404 Not Found The 404 (Not Found) status code indicates that the origin server did not find a current representation for the target resource or is not willing to disclose that one exists. A 404 status code does not indicate whether this lack of representation is temporary or permanent; the 410 (Gone) status code is preferred over 404 if the origin server knows, presumably through some configurable means, that the condition is likely to be permanent. A 404 response is cacheable by default; i.e., unless otherwise indicated by the method definition or explicit cache controls (see Section 4.2.2 of [RFC7234]).

而引起质疑的主要是上述语境中对资源的定义。 根据同一个RFC(7231)， resource的定义是:

Resources: The target of an HTTP request is called a "resource". HTTP does not limit the nature of a resource; it merely defines an interface that might be used to interact with resources. Each resource is identified by a Uniform Resource Identifier (URI), as described in Section 2.7 of [RFC7230]. When a client constructs an HTTP/1.1 request message, it sends the target URI in one of various forms, as defined in (Section 5.3 of [RFC7230]). When a request is received, the server reconstructs an effective request URI for the target resource (Section 5.5 of [RFC7230]). One design goal of HTTP is to separate resource identification from request semantics, which is made possible by vesting the request semantics in the request method (Section 4) and a few request-modifying header fields (Section 5). If there is a conflict between the method semantics and any semantic implied by the URI itself, as described in Section 4.2.1, the method semantics take precedence.

所以在我的理解中，404状态代码不应该用于成功的GET请求，结果为空。(例如:一个没有特定过滤器结果的列表)

这里有两个问题。一个在标题中，一个在例子中。我认为，这在一定程度上导致了关于哪种反应是合适的争议。

问题标题询问空数据。空数据仍然是数据，但不等于没有数据。因此，这意味着请求一个结果集，即一个列表，可能来自/users。如果一个列表是空的，它仍然是一个列表，因此204(无内容)是最合适的。您刚刚请求了一个用户列表，并得到了一个列表，它只是碰巧没有内容。

相反，所提供的示例询问了一个特定的对象，一个用户/users/9。如果没有找到用户#9，则不返回任何用户对象。您请求一个特定的资源(一个用户对象)，但由于没有找到而没有得到它，因此404是合适的。

我认为解决这个问题的方法是，如果您可以在不添加任何条件语句的情况下使用响应，那么使用204，否则使用404。

在我的例子中，我可以迭代一个空列表而不检查它是否有内容，但是我不能在一个空对象上显示用户对象数据而不破坏一些东西或添加一个检查来查看它是否为空。

当然，如果适合您的需要，您可以使用空对象模式返回一个对象，但这是另一个线程的讨论。