现有的答案没有详细说明使用路径参数还是查询参数是有区别的。

In case of path parameters, the parameter is part of the resource path. In case of /users/9, the response should be 404 because that resource was not found. /users/9 is the resource, and the result is unary, or an error, it doesn't exist. This is not a monad. In case of query parameters, the parameter is not part of the resource path. In case of /users?id=9, the response should be 204 because the resource /users was found but it could not return any data. The resource /users exists and the result is n-ary, it exists even if it is empty. If id is unique, this is a monad.

使用路径参数还是查询参数取决于用例。我更喜欢将路径参数用于强制的、规范的或标识参数，将查询参数用于可选的、非规范的或属性参数(如分页、排序区域设置等)。在REST API中，我会使用/users/9而不是/users?Id =9，特别是因为可能嵌套获取“子记录”，如/users/9/ SSH -keys/0获取第一个公共SSH密钥或/users/9/address/2获取第三个邮政地址。

我更喜欢使用404。原因如下:

Calls for unary (1 result) and n-ary (n results) methods should not vary for no good reason. I like to have the same response codes if possible. The number of expected results is of course a difference, say, you expect the body to be an object (unary) or an array of objects (n-ary). For n-ary, I would return an array, and in case there are not results, I would not return no set (no document), I would return an empty set (empty document, like empty array in JSON or empty element in XML). That is, it's still 200 but with zero records. There's no reason to put this information on the wire other than in the body. 204 is like a void method. I would not use it for GET, only for POST, PUT, and DELETE. I make an exception in case of GET where the identifiers are query parameters not path parameters. Not finding the record is like NoSuchElementException, ArrayIndexOutOfBoundsException or something like that, caused by the client using an id that doesn't exist, so, it's a client error. From a code perspective, getting 204 means an additional branch in the code that could be avoided. It complicates client code, and in some cases it also complicates server code (depending on whether you use entity/model monads or plain entities/models; and I strongly recommend staying away from entity/model monads, it can lead to nasty bugs where because of the monad you think an operation is successful and return 200 or 204 when you should actually have returned something else). Client code is easier to write and understand if 2xx means the server did what the client requested, and 4xx means the server didn't do what the client requested and it's the client's fault. Not giving the client the record that the client requested by id is the client's fault, because the client requested an id that doesn't exist.

最后一点:一致性

GET /用户/ 9 PUT /users/9和DELETE /users/9

PUT /users/9和DELETE /users/9已经必须在成功更新或删除的情况下返回204。如果用户9不存在，它们应该返回什么?根据所使用的HTTP方法将相同的情况显示为不同的状态代码是没有意义的。

Besides, not a normative, but a cultural reason: If 204 is used for GET /users/9 next thing that will happen in the project is that somebody thinks returning 204 is good for n-ary methods. And that complicates client code, because instead of just checking for 2xx and then decoding the body, the client now has to specifically check for 204 and in that case skip decoding the body. Bud what does the client do instead? Create an empty array? Why not have that on the wire, then? If the client creates the empty array, 204 is a form of stupid compression. If the client uses null instead, a whole different can of worms is opened.

Twitter使用404，并带有类似“找不到数据”的自定义错误消息。

裁判:https://developer.twitter.com/en/docs/basics/response-codes.html

起初，我认为204是有意义的，但经过讨论，我相信404是唯一真正正确的回答。考虑以下数据:

用户:约翰，彼得

METHOD  URL                      STATUS  RESPONSE
GET     /users                   200     [John, Peter]
GET     /users/john              200     John
GET     /unknown-url-egaer       404     Not Found
GET     /users/kyle              404     User Not found
GET     /users?name=kyle`        200     []
DELETE  /users/john              204     No Content

背景知识:

the search returns an array, it just didn't have any matches but it has content: an empty array. 404 is of course best known for url's that aren't supported by the requested server, but a missing resource is in fact the same. Even though /users/:name is matched with users/kyle, the user Kyle is not available resource so a 404 still applies. It isn't a search query, it is a direct reference by a dynamic url, so 404 it is. After suggestions in the comments, customizing the message of the 404 is another way of helping out the API consumer to even better distinguish between complete unknown routes and missing entities.

不管怎样，我的意见。

TL;DR:使用404

请看这个博客。这解释得很好。

博客对204的评论总结如下:

204 No Content作为浏览器的响应代码并不是特别有用(尽管根据HTTP规范，浏览器需要将其理解为“不要更改视图”的响应代码)。 然而，No Content对于ajax web服务非常有用，它可能想要表示成功而不需要返回任何东西。(特别是在DELETE或post这样不需要反馈的情况下)。

因此，您的问题的答案是在您的情况下使用404。204是一个专门的响应代码，您不应该经常将其返回给浏览器以响应GET。

其他响应代码甚至比204和404更不合适:

200 should be returned with the body of whatever you successfully fetched. Not appropriate when the entity you're fetching doesn't exist. 202 is used when the server has begun work on an object but the object isn't fully ready yet. Certainly not the case here. You haven't begun, nor will you begin, construction of user 9 in response to a GET request. That breaks all sorts of rules. 400 is used in response to a poorly formatted HTTP request (for instance malformed http headers, incorrectly ordered segments, etc). This will almost certainly be handled by whatever framework you're using. You shouldn't have to deal with this unless you're writing your own server from scratch. Edit: Newer RFCs now allow for 400 to be used for semantically invalid requests.

维基百科对HTTP状态码的描述尤其有用。 您也可以在www.w3.org上看到HTTP/1.1 RFC2616文档中的定义

如果期望资源存在，但它可能是空的，我认为它可能更容易得到一个200 OK的表示，表明这个东西是空的。

因此，我宁愿让/things返回一个带有{"Items":[]}的200 OK，而不是一个没有任何内容的204，因为这样，一个包含0项的集合可以被视为一个包含一个或多个项目的集合。

我将把204 No Content留给put和delete，在这种情况下，可能真的没有有用的表示。

在/thing/9不存在的情况下，404是合适的。

为什么不用410呢?它表示所请求的资源不再存在，客户端希望永远不会对该资源发出请求，在您的例子中是users/9。

你可以在这里找到更多关于410的详细信息:https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html