引用
1.1 消息1xx（Informational 1xx）
该类状态代码用于表示临时回应。临时回应由状态行（Status-Line）及可选标题组成， 由空行终止。HTTP/1.0中没有定义任何1xx的状态代码，所以它们不是对HTTP/1.0请求的 合法回应。实际上，它们主要用于实验用途，这已经超出本文档的范围。
1.2 成功2xx（Successful 2xx）
表示客户端请求被成功接收、理解、接受。
200 OK
请求成功。回应的信息依赖于请求所使用的方法，如下：
GET 要请求的资源已经放在回应的实体中了。
HEAD 没有实体主体，回应中只包括标题信息。
POST 实体（描述或包含操作的结果）。
201 Created
请求完成，结果是创建了新资源。新创建资源的URI可在回应的实体中得到。原始服务器应在发出该状态代码前创建该资源。如果该操作不能立即完成，服务器必须在该资源可用时在回应主体中给出提示，否则，服务器端应回应202（可被接受）。
在本文定义的方法，只有POST可以创建资源。
202 Accepted
请求被接受，但处理尚未完成。请求可能不一定会最终完成，有可能被处理过程随时中断，在这种情况下，没有办法在异步操作中重新发送状态代码。
202回应是没有义务的，这样做的目的是允许服务器不必等到用户代理和服务器间的连接结束，就可以响应其它过程的请求（象每天运行一次的，基于批处理的过程）。
在某些回应中返回的实体中包括当前请求的状态指示、状态监视器指针或用户对请求能否实现的评估信息。
204 No Content
服务器端已经实现了请求，但是没有返回新的信息。如果客户是用户代理，则勿需为此更新自身的文档视图。该回应主要是为了在不影响用户代理激活文档视图的前提下，进行script语句的输入及其它操作。该回应还可能包括新的、以实体标题形式表示的元信息，它可被当前用户代理激活视图中的文档所使用。
1.3 重定向（Redirection 3xx）
该类状态码表示用户代理要想完成请求，还需要发出进一步的操作。这些操作只有当后跟的请求是GET或HEAD时，才可由用户代理来实现，而不用与用户进行交互。用户代理永远也不要对请求进行5次以上的重定向操作，这样可能导致无限循环。
300 Multiple Choices
该状态码不被HTTP/1.0的应用程序直接使用，只是做为3xx类型回应的缺省解释。存在多个可用的被请求资源。
除非是HEAD请求，否则回应的实体中必须包括这些资源的字符列表及位置信息，由用户或用户代理来决定哪个是最适合的。
如果服务器有首选，它应将对应的URL信息存放在位置域（Location field）处，用户代理会根据此域的值来实现自动的重定向。
301 Moved Permanently
请求到的资源都会分配一个永久的URL，这样就可以在将来通过该URL来访问此资源。有编辑链接功能的客户端会尽可能地根据服务器端传回的新链接而自动更新请求URI。 新的URL必须由回应中的位置域指定。除非是HEAD请求，否则回应的实体主体 （Entity-Body）必须包括对新URL超链接的简要描述。
如果用POST方法发出请求，而接收到301回应状态码。在这种情况下，除非用户确认，否则用户代理不必自动重定向请求，因为这将导致改变已发出请求的环境。
注意：当在接收到301状态码后而自动重定向POST请求时，一些现存的用户代理会错误地将其改为GET请求。
302 Moved Temporarily
请求到的资源在一个不同的URL处临时保存。因为重定向有时会被更改，客户端应继续用请求URI来发出以后的请求。新的URL必须由回应中的位置域指定。除非是HEAD请求，否则回应的实体主体 （Entity-Body）必须包括对新URL超链接的简要描述。
如果用POST方法发出请求，而接收到302回应状态码。在这种情况下，除非用户确认，否则用户代理不必自动重定向请求，因为这将导致改变已发出请求的环境。
注意：当在接收到302状态码后而自动重定向POST请求时，一些现存的用户代理会错误地将其改为GET请求。
304 Not Modified
如果客户端成功执行了条件GET请求，而对应文件自If-Modified-Since域所指定的日期以来就没有更新过，服务器应当回应此状态码，而不是将实体主体发送给客户端。回应标题域中只应包括一些相关信息，比如缓存管理器、与实体最近更新（entity's Last-Modified）日期无关的修改。相关标题域的例子有：日期、服务器、过期时间。每当304回应中给出的域值发生变化，缓存都应当对缓存的实体进行更新。
1.4 客户端错误（Client Error ）4xx
4xx类的状态码表示客户端发生错误。如果客户端在收到4xx代码时请求还没有完成，它应当立即终止向服务器发送数据。除了回应HEAD请求外，不论错误是临时的还是永久的，服务器端都必须在回应的实体中包含错误状态的解释。这些状态码适用于任何请求方法。
注意：如果客户端正在发送数据，服务器端的TCP实现应当小心，以确保客户端在关闭输入连接之前收到回应包。如果客户端在关闭后仍旧向服务器发送数据，服务器会给客户 端发送一个复位包，清空客户端尚未处理的输入缓冲区，以终止HTTP应用程序的读取、解释活动。
400 非法请求（Bad Request）
如果请求的语法不对，服务器将无法理解。客户端在对该请求做出更改之前，不应再次向服务器重复发送该请求。
401 未授权（Unauthorized）
请求需要用户授权。回应中的WWW-Authenticate标题域（10.16节）应提示用户以授权方式请求资源。客户端应使用合适的授权标题域（10.2节）来重复该请求。如果请求中已经包括了授权信任信息，那回应的401表示此授权被拒绝。如果用户代理在多次尝试之后，回应一样还是返回401状态代码，用户应当察看一下回应的实体，因为在实体中会包括一些相关的动态信息。HTTP访问授权会在11节中解释。
403 禁止（Forbidden）
服务器理解请求，但是拒绝实现该请求。授权对此没有帮助，客户端应当停止重复发送此请求。如果不是用HEAD请求方法，而且服务器端愿意公布请求未被实现原因的前提下，服务器会将拒绝原因写在回应实体中。该状态码一般用于服务器端不想公布请求被拒绝的细节或没有其它的回应可用。
404 没有找到（Not Found）
服务器没有找到与请求URI相符的资源。404状态码并不指明状况是临时性的还是永久性的。如果服务器不希望为客户端提供这方面的信息，还回应403（禁止）状态码。
1.5 服务器错误（Server Error ）5xx
回应代码以‘5’开头的状态码表示服务器端发现自己出现错误，不能继续执行请求。如果客户端在收到5xx状态码时，请求尚未完成，它应当立即停止向服务器发送数据。除了回应HEAD请求外，服务器应当在其回应实体中包括对错误情况的解释、并指明是临时性的还永久性的。
这类回应代码没有标题域，可适用于任何请求方法。
500 服务器内部错误（Internal Server Error）
服务器碰到了意外情况，使其无法继续回应请求。
501 未实现（Not Implemented）
服务器无法提供对请求中所要求功能的支持。如果服务器无法识别请求方法就会回应此状态代码，这意味着不能回应请求所要求的任何资源。
502 非法网关（Bad Gateway）
充当网关或代理的服务器从要发送请求的上游（upstream）服务器收到非法的回应。
503 服务不可用（Service Unavailable）
服务器当前无法处理请求。这一般是由于服务器临时性超载或维护引起的。该状态码暗示情况是暂时性的，要产生一些延迟。
注意：503状态码并没有暗示服务器在超载时一定要返回此状态码。一些服务器可能希望在超载时采用简单处理，即断掉连接。
----------------------------英文原文-----------------------
Each Status-Code is described below, including a description of which method(s) it can follow and any metainformation required in the response.
10.1 Informational 1xx
This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any 1xx status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client except under experimental conditions.
A client MUST be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100 (Continue) status message. Unexpected 1xx status responses MAY be ignored by a user agent.
Proxies MUST forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself requested the generation of the 1xx response. (For example, if a
proxy adds a "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding 100 (Continue) response(s).)
10.1.1 100 Continue
The client SHOULD continue with its request. This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed. See section 8.2.3 for detailed discussion of the use and handling of this status code.
10.1.2 101 Switching Protocols
The server understands and is willing to comply with the client's request, via the Upgrade message header field (section 14.42), for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response's Upgrade header field immediately after the empty line which terminates the 101 response.
The protocol SHOULD be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features.
10.2 Successful 2xx
This class of status code indicates that the client's request was successfully received, understood, and accepted.
10.2.1 200 OK
The request has succeeded. The information returned with the response is dependent on the method used in the request, for example:
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.
10.2.2 201 Created
The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field. The response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. The origin server MUST create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server SHOULD respond with 202 (Accepted) response instead.
A 201 response MAY contain an ETag response header field indicating the current value of the entity tag for the requested variant just created, see section 14.19.
10.2.3 202 Accepted
The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status code from an asynchronous operation such as this.
The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the server persist until the process is completed. The entity returned with this response SHOULD include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the user can expect the request to be fulfilled.
10.2.4 203 Non-Authoritative Information
The returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered from a local or a third-party copy. The set presented MAY be a subset or superset of the original version. For example, including local annotation information about the resource might result in a superset of the metainformation known by the origin server. Use of this response code is not required and is only appropriate when the response would otherwise be 200 (OK).
10.2.5 204 No Content
The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.
If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent's active view.
The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.
10.2.6 205 Reset Content
The server has fulfilled the request and the user agent SHOULD reset the document view which caused the request to be sent. This response is primarily intended to allow input for actions to take place via user input, followed by a clearing of the form in which the input is given so that the user can easily initiate another input action. The response MUST NOT include an entity.
10.2.7 206 Partial Content
The server has fulfilled the partial GET request for the resource. The request MUST have included a Range header field (section 14.35) indicating the desired range, and MAY have included an If-Range header field (section 14.27) to make the request conditional.
The response MUST include the following header fields:
- Either a Content-Range header field (section 14.16) indicating
the range included with this response, or a multipart/byteranges
Content-Type including Content-Range fields for each part. If a
Content-Length header field is present in the response, its
value MUST match the actual number of OCTETs transmitted in the
message-body.
- Date
- ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
- Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant
If the 206 response is the result of an If-Range request that used a strong cache validator (see section 13.3.3), the response SHOULD NOT include other entity-headers. If the response is the result of an If-Range request that used a weak validator, the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. Otherwise, the response MUST include all of the entity-headers that would have been returned with a 200 (OK) response to the same request.
A cache MUST NOT combine a 206 response with other previously cached content if the ETag or Last-Modified headers do not match exactly, see 13.5.4.
A cache that does not support the Range and Content-Range headers MUST NOT cache 206 (Partial) responses.
10.3 Redirection 3xx
This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. The action required MAY be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD. A client SHOULD detect infinite redirection loops, since such loops generate network traffic for each redirection.
Note: previous versions of this specification recommended a
maximum of five redirections. Content developers should be aware
that there might be clients that implement such a fixed
limitation.
10.3.1 300 Multiple Choices
The requested resource corresponds to any one of a set of representations, each with its own specific location, and agent- driven negotiation information (section 12) is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that location.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content- Type header field. Depending upon the format and the capabilities of
the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
If the server has a preferred choice of representation, it SHOULD include the specific URI for that representation in the Location field; user agents MAY use the Location field value for automatic redirection. This response is cacheable unless indicated otherwise.
10.3.2 301 Moved Permanently
The requested resource has been assigned a new permanent URI and any future references to this resource SHOULD use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.
The new permanent URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
10.3.3 302 Found
The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 302 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: RFC 1945 and RFC 2068 specify that the client is not allowed
to change the method on the redirected request. However, most
existing user agent implementations treat 302 as if it were a 303
response, performing a GET on the Location field-value regardless
of the original request method. The status codes 303 and 307 have
been added for servers that wish to make unambiguously clear which
kind of reaction is expected of the client.
10.3.4 303 See Other
The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre-HTTP/1.1 user agents do not understand the 303
status. When interoperability with such clients is a concern, the
302 status code may be used instead, since most user agents react
to a 302 response as described here for 303.
10.3.5 304 Not Modified
If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields.
The response MUST include the following header fields:
- Date, unless its omission is required by section 14.18.1
If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without one (as already specified by [RFC 2068], section 14.19), caches will operate correctly.
- ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
- Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant
If the conditional GET used a strong cache validator (see section 13.3.3), the response SHOULD NOT include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
If a 304 response indicates an entity not currently cached, then the cache MUST disregard the response and repeat the request without the conditional.
If a cache uses a received 304 response to update a cache entry, the cache MUST update the entry to reflect any new field values given in the response.
10.3.6 305 Use Proxy
The requested resource MUST be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses MUST only be generated by origin servers.
Note: RFC 2068 was not clear that 305 was intended to redirect a
single request, and to be generated by origin servers only. Not
observing these limitations has significant security consequences.
10.3.7 306 (Unused)
The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.
10.3.8 307 Temporary Redirect
The requested resource resides temporarily under a different URI. Since the redirection MAY be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s) , since many pre-HTTP/1.1 user agents do not understand the 307 status. Therefore, the note SHOULD contain the information necessary for a user to repeat the original request on the new URI.
If the 307 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
10.4 Client Error 4xx
The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents SHOULD display any included entity to the user.
If the client is sending data, a server implementation using TCP SHOULD be careful to ensure that the client acknowledges receipt of the packet(s) containing the response, before the server closes the input connection. If the client continues sending data to the server after the close, the server's TCP stack will send a reset packet to the client, which may erase the client's unacknowledged input buffers before they can be read and interpreted by the HTTP application.
10.4.1 400 Bad Request
The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
10.4.2 401 Unauthorized
The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (section 14.8). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
10.4.3 402 Payment Required
This code is reserved for future use.
10.4.4 403 Forbidden
The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it SHOULD describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not Found) can be used instead.
10.4.5 404 Not Found
The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.
10.4.6 405 Method Not Allowed
The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
10.4.7 406 Not Acceptable
The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of available entity characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept headers sent in the
request. In some cases, this may even be preferable to sending a
406 response. User agents are encouraged to inspect the headers of
an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.
10.4.8 407 Proxy Authentication Required
This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy MUST return a Proxy-Authenticate header field (section 14.33) containing a challenge applicable to the proxy for the requested resource. The client MAY repeat the request with a suitable Proxy-Authorization header field (section 14.34). HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
10.4.9 408 Request Timeout
The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.
10.4.10 409 Conflict
The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body SHOULD include enough
information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.
10.4.11 410 Gone
The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent. Clients with link editing capabilities SHOULD delete references to the Request-URI after user approval. If the server does not know, or has no facility to determine, whether or not the condition is permanent, the status code 404 (Not Found) SHOULD be used instead. This response is cacheable unless indicated otherwise.
The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time -- that is left to the discretion of the server owner.
10.4.12 411 Length Required
The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request message.
10.4.13 412 Precondition Failed
The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.
10.4.14 413 Request Entity Too Large
The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server MAY close the connection to prevent the client from continuing the request.
If the condition is temporary, the server SHOULD include a Retry- After header field to indicate that it is temporary and after what time the client MAY try again.
10.4.15 414 Request-URI Too Long
The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some servers using fixed-length buffers for reading or manipulating the Request-URI.
10.4.16 415 Unsupported Media Type
The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
10.4.17 416 Requested Range Not Satisfiable
A server SHOULD return a response with this status code if a request included a Range request-header field (section 14.35), and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field. (For byte-ranges, this means that the first- byte-pos of all of the byte-range-spec values were greater than the current length of the selected resource.)
When this status code is returned for a byte-range request, the response SHOULD include a Content-Range entity-header field specifying the current length of the selected resource (see section 14.16). This response MUST NOT use the multipart/byteranges content- type.
10.4.18 417 Expectation Failed
The expectation given in an Expect request-header field (see section 14.20) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.
10.5 Server Error 5xx
Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable of performing the request. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. User agents SHOULD display any included entity to the user. These response codes are applicable to any request method.
10.5.1 500 Internal Server Error
The server encountered an unexpected condition which prevented it from fulfilling the request.
10.5.2 501 Not Implemented
The server does not support the functionality required to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.
10.5.3 502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request.
10.5.4 503 Service Unavailable
The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay MAY be indicated in a Retry-After header. If no Retry-After is given, the client SHOULD handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may wish
to simply refuse the connection.
10.5.5 504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
Note: Note to implementors: some deployed proxies are known to
return 400 or 500 when DNS lookups time out.
10.5.6 505 HTTP Version Not Supported
The server does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described in section 3.1, other than with this error message. The response SHOULD contain an entity describing why that version is not supported and what other protocols are supported by that server.
该类状态代码用于表示临时回应。临时回应由状态行（Status-Line）及可选标题组成， 由空行终止。HTTP/1.0中没有定义任何1xx的状态代码，所以它们不是对HTTP/1.0请求的 合法回应。实际上，它们主要用于实验用途，这已经超出本文档的范围。
1.2 成功2xx（Successful 2xx）
表示客户端请求被成功接收、理解、接受。
200 OK
请求成功。回应的信息依赖于请求所使用的方法，如下：
GET 要请求的资源已经放在回应的实体中了。
HEAD 没有实体主体，回应中只包括标题信息。
POST 实体（描述或包含操作的结果）。
201 Created
请求完成，结果是创建了新资源。新创建资源的URI可在回应的实体中得到。原始服务器应在发出该状态代码前创建该资源。如果该操作不能立即完成，服务器必须在该资源可用时在回应主体中给出提示，否则，服务器端应回应202（可被接受）。
在本文定义的方法，只有POST可以创建资源。
202 Accepted
请求被接受，但处理尚未完成。请求可能不一定会最终完成，有可能被处理过程随时中断，在这种情况下，没有办法在异步操作中重新发送状态代码。
202回应是没有义务的，这样做的目的是允许服务器不必等到用户代理和服务器间的连接结束，就可以响应其它过程的请求（象每天运行一次的，基于批处理的过程）。
在某些回应中返回的实体中包括当前请求的状态指示、状态监视器指针或用户对请求能否实现的评估信息。
204 No Content
服务器端已经实现了请求，但是没有返回新的信息。如果客户是用户代理，则勿需为此更新自身的文档视图。该回应主要是为了在不影响用户代理激活文档视图的前提下，进行script语句的输入及其它操作。该回应还可能包括新的、以实体标题形式表示的元信息，它可被当前用户代理激活视图中的文档所使用。
1.3 重定向（Redirection 3xx）
该类状态码表示用户代理要想完成请求，还需要发出进一步的操作。这些操作只有当后跟的请求是GET或HEAD时，才可由用户代理来实现，而不用与用户进行交互。用户代理永远也不要对请求进行5次以上的重定向操作，这样可能导致无限循环。
300 Multiple Choices
该状态码不被HTTP/1.0的应用程序直接使用，只是做为3xx类型回应的缺省解释。存在多个可用的被请求资源。
除非是HEAD请求，否则回应的实体中必须包括这些资源的字符列表及位置信息，由用户或用户代理来决定哪个是最适合的。
如果服务器有首选，它应将对应的URL信息存放在位置域（Location field）处，用户代理会根据此域的值来实现自动的重定向。
301 Moved Permanently
请求到的资源都会分配一个永久的URL，这样就可以在将来通过该URL来访问此资源。有编辑链接功能的客户端会尽可能地根据服务器端传回的新链接而自动更新请求URI。 新的URL必须由回应中的位置域指定。除非是HEAD请求，否则回应的实体主体 （Entity-Body）必须包括对新URL超链接的简要描述。
如果用POST方法发出请求，而接收到301回应状态码。在这种情况下，除非用户确认，否则用户代理不必自动重定向请求，因为这将导致改变已发出请求的环境。
注意：当在接收到301状态码后而自动重定向POST请求时，一些现存的用户代理会错误地将其改为GET请求。
302 Moved Temporarily
请求到的资源在一个不同的URL处临时保存。因为重定向有时会被更改，客户端应继续用请求URI来发出以后的请求。新的URL必须由回应中的位置域指定。除非是HEAD请求，否则回应的实体主体 （Entity-Body）必须包括对新URL超链接的简要描述。
如果用POST方法发出请求，而接收到302回应状态码。在这种情况下，除非用户确认，否则用户代理不必自动重定向请求，因为这将导致改变已发出请求的环境。
注意：当在接收到302状态码后而自动重定向POST请求时，一些现存的用户代理会错误地将其改为GET请求。
304 Not Modified
如果客户端成功执行了条件GET请求，而对应文件自If-Modified-Since域所指定的日期以来就没有更新过，服务器应当回应此状态码，而不是将实体主体发送给客户端。回应标题域中只应包括一些相关信息，比如缓存管理器、与实体最近更新（entity's Last-Modified）日期无关的修改。相关标题域的例子有：日期、服务器、过期时间。每当304回应中给出的域值发生变化，缓存都应当对缓存的实体进行更新。
1.4 客户端错误（Client Error ）4xx
4xx类的状态码表示客户端发生错误。如果客户端在收到4xx代码时请求还没有完成，它应当立即终止向服务器发送数据。除了回应HEAD请求外，不论错误是临时的还是永久的，服务器端都必须在回应的实体中包含错误状态的解释。这些状态码适用于任何请求方法。
注意：如果客户端正在发送数据，服务器端的TCP实现应当小心，以确保客户端在关闭输入连接之前收到回应包。如果客户端在关闭后仍旧向服务器发送数据，服务器会给客户 端发送一个复位包，清空客户端尚未处理的输入缓冲区，以终止HTTP应用程序的读取、解释活动。
400 非法请求（Bad Request）
如果请求的语法不对，服务器将无法理解。客户端在对该请求做出更改之前，不应再次向服务器重复发送该请求。
401 未授权（Unauthorized）
请求需要用户授权。回应中的WWW-Authenticate标题域（10.16节）应提示用户以授权方式请求资源。客户端应使用合适的授权标题域（10.2节）来重复该请求。如果请求中已经包括了授权信任信息，那回应的401表示此授权被拒绝。如果用户代理在多次尝试之后，回应一样还是返回401状态代码，用户应当察看一下回应的实体，因为在实体中会包括一些相关的动态信息。HTTP访问授权会在11节中解释。
403 禁止（Forbidden）
服务器理解请求，但是拒绝实现该请求。授权对此没有帮助，客户端应当停止重复发送此请求。如果不是用HEAD请求方法，而且服务器端愿意公布请求未被实现原因的前提下，服务器会将拒绝原因写在回应实体中。该状态码一般用于服务器端不想公布请求被拒绝的细节或没有其它的回应可用。
404 没有找到（Not Found）
服务器没有找到与请求URI相符的资源。404状态码并不指明状况是临时性的还是永久性的。如果服务器不希望为客户端提供这方面的信息，还回应403（禁止）状态码。
1.5 服务器错误（Server Error ）5xx
回应代码以‘5’开头的状态码表示服务器端发现自己出现错误，不能继续执行请求。如果客户端在收到5xx状态码时，请求尚未完成，它应当立即停止向服务器发送数据。除了回应HEAD请求外，服务器应当在其回应实体中包括对错误情况的解释、并指明是临时性的还永久性的。
这类回应代码没有标题域，可适用于任何请求方法。
500 服务器内部错误（Internal Server Error）
服务器碰到了意外情况，使其无法继续回应请求。
501 未实现（Not Implemented）
服务器无法提供对请求中所要求功能的支持。如果服务器无法识别请求方法就会回应此状态代码，这意味着不能回应请求所要求的任何资源。
502 非法网关（Bad Gateway）
充当网关或代理的服务器从要发送请求的上游（upstream）服务器收到非法的回应。
503 服务不可用（Service Unavailable）
服务器当前无法处理请求。这一般是由于服务器临时性超载或维护引起的。该状态码暗示情况是暂时性的，要产生一些延迟。
注意：503状态码并没有暗示服务器在超载时一定要返回此状态码。一些服务器可能希望在超载时采用简单处理，即断掉连接。
----------------------------英文原文-----------------------
Each Status-Code is described below, including a description of which method(s) it can follow and any metainformation required in the response.
10.1 Informational 1xx
This class of status code indicates a provisional response, consisting only of the Status-Line and optional headers, and is terminated by an empty line. There are no required headers for this class of status code. Since HTTP/1.0 did not define any 1xx status codes, servers MUST NOT send a 1xx response to an HTTP/1.0 client except under experimental conditions.
A client MUST be prepared to accept one or more 1xx status responses prior to a regular response, even if the client does not expect a 100 (Continue) status message. Unexpected 1xx status responses MAY be ignored by a user agent.
Proxies MUST forward 1xx responses, unless the connection between the proxy and its client has been closed, or unless the proxy itself requested the generation of the 1xx response. (For example, if a
proxy adds a "Expect: 100-continue" field when it forwards a request, then it need not forward the corresponding 100 (Continue) response(s).)
10.1.1 100 Continue
The client SHOULD continue with its request. This interim response is used to inform the client that the initial part of the request has been received and has not yet been rejected by the server. The client SHOULD continue by sending the remainder of the request or, if the request has already been completed, ignore this response. The server MUST send a final response after the request has been completed. See section 8.2.3 for detailed discussion of the use and handling of this status code.
10.1.2 101 Switching Protocols
The server understands and is willing to comply with the client's request, via the Upgrade message header field (section 14.42), for a change in the application protocol being used on this connection. The server will switch protocols to those defined by the response's Upgrade header field immediately after the empty line which terminates the 101 response.
The protocol SHOULD be switched only when it is advantageous to do so. For example, switching to a newer version of HTTP is advantageous over older versions, and switching to a real-time, synchronous protocol might be advantageous when delivering resources that use such features.
10.2 Successful 2xx
This class of status code indicates that the client's request was successfully received, understood, and accepted.
10.2.1 200 OK
The request has succeeded. The information returned with the response is dependent on the method used in the request, for example:
GET an entity corresponding to the requested resource is sent in the response;
HEAD the entity-header fields corresponding to the requested resource are sent in the response without any message-body;
POST an entity describing or containing the result of the action;
TRACE an entity containing the request message as received by the end server.
10.2.2 201 Created
The request has been fulfilled and resulted in a new resource being created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific URI for the resource given by a Location header field. The response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. The origin server MUST create the resource before returning the 201 status code. If the action cannot be carried out immediately, the server SHOULD respond with 202 (Accepted) response instead.
A 201 response MAY contain an ETag response header field indicating the current value of the entity tag for the requested variant just created, see section 14.19.
10.2.3 202 Accepted
The request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place. There is no facility for re-sending a status code from an asynchronous operation such as this.
The 202 response is intentionally non-committal. Its purpose is to allow a server to accept a request for some other process (perhaps a batch-oriented process that is only run once per day) without requiring that the user agent's connection to the server persist until the process is completed. The entity returned with this response SHOULD include an indication of the request's current status and either a pointer to a status monitor or some estimate of when the user can expect the request to be fulfilled.
10.2.4 203 Non-Authoritative Information
The returned metainformation in the entity-header is not the definitive set as available from the origin server, but is gathered from a local or a third-party copy. The set presented MAY be a subset or superset of the original version. For example, including local annotation information about the resource might result in a superset of the metainformation known by the origin server. Use of this response code is not required and is only appropriate when the response would otherwise be 200 (OK).
10.2.5 204 No Content
The server has fulfilled the request but does not need to return an entity-body, and might want to return updated metainformation. The response MAY include new or updated metainformation in the form of entity-headers, which if present SHOULD be associated with the requested variant.
If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This response is primarily intended to allow input for actions to take place without causing a change to the user agent's active document view, although any new or updated metainformation SHOULD be applied to the document currently in the user agent's active view.
The 204 response MUST NOT include a message-body, and thus is always terminated by the first empty line after the header fields.
10.2.6 205 Reset Content
The server has fulfilled the request and the user agent SHOULD reset the document view which caused the request to be sent. This response is primarily intended to allow input for actions to take place via user input, followed by a clearing of the form in which the input is given so that the user can easily initiate another input action. The response MUST NOT include an entity.
10.2.7 206 Partial Content
The server has fulfilled the partial GET request for the resource. The request MUST have included a Range header field (section 14.35) indicating the desired range, and MAY have included an If-Range header field (section 14.27) to make the request conditional.
The response MUST include the following header fields:
- Either a Content-Range header field (section 14.16) indicating
the range included with this response, or a multipart/byteranges
Content-Type including Content-Range fields for each part. If a
Content-Length header field is present in the response, its
value MUST match the actual number of OCTETs transmitted in the
message-body.
- Date
- ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
- Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant
If the 206 response is the result of an If-Range request that used a strong cache validator (see section 13.3.3), the response SHOULD NOT include other entity-headers. If the response is the result of an If-Range request that used a weak validator, the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers. Otherwise, the response MUST include all of the entity-headers that would have been returned with a 200 (OK) response to the same request.
A cache MUST NOT combine a 206 response with other previously cached content if the ETag or Last-Modified headers do not match exactly, see 13.5.4.
A cache that does not support the Range and Content-Range headers MUST NOT cache 206 (Partial) responses.
10.3 Redirection 3xx
This class of status code indicates that further action needs to be taken by the user agent in order to fulfill the request. The action required MAY be carried out by the user agent without interaction with the user if and only if the method used in the second request is GET or HEAD. A client SHOULD detect infinite redirection loops, since such loops generate network traffic for each redirection.
Note: previous versions of this specification recommended a
maximum of five redirections. Content developers should be aware
that there might be clients that implement such a fixed
limitation.
10.3.1 300 Multiple Choices
The requested resource corresponds to any one of a set of representations, each with its own specific location, and agent- driven negotiation information (section 12) is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that location.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of resource characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content- Type header field. Depending upon the format and the capabilities of
the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
If the server has a preferred choice of representation, it SHOULD include the specific URI for that representation in the Location field; user agents MAY use the Location field value for automatic redirection. This response is cacheable unless indicated otherwise.
10.3.2 301 Moved Permanently
The requested resource has been assigned a new permanent URI and any future references to this resource SHOULD use one of the returned URIs. Clients with link editing capabilities ought to automatically re-link references to the Request-URI to one or more of the new references returned by the server, where possible. This response is cacheable unless indicated otherwise.
The new permanent URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 301 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
10.3.3 302 Found
The requested resource resides temporarily under a different URI. Since the redirection might be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
If the 302 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
Note: RFC 1945 and RFC 2068 specify that the client is not allowed
to change the method on the redirected request. However, most
existing user agent implementations treat 302 as if it were a 303
response, performing a GET on the Location field-value regardless
of the original request method. The status codes 303 and 307 have
been added for servers that wish to make unambiguously clear which
kind of reaction is expected of the client.
10.3.4 303 See Other
The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource. This method exists primarily to allow the output of a POST-activated script to redirect the user agent to a selected resource. The new URI is not a substitute reference for the originally requested resource. The 303 response MUST NOT be cached, but the response to the second (redirected) request might be cacheable.
The different URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s).
Note: Many pre-HTTP/1.1 user agents do not understand the 303
status. When interoperability with such clients is a concern, the
302 status code may be used instead, since most user agents react
to a 302 response as described here for 303.
10.3.5 304 Not Modified
If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code. The 304 response MUST NOT contain a message-body, and thus is always terminated by the first empty line after the header fields.
The response MUST include the following header fields:
- Date, unless its omission is required by section 14.18.1
If a clockless origin server obeys these rules, and proxies and clients add their own Date to any response received without one (as already specified by [RFC 2068], section 14.19), caches will operate correctly.
- ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
- Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same
variant
If the conditional GET used a strong cache validator (see section 13.3.3), the response SHOULD NOT include other entity-headers. Otherwise (i.e., the conditional GET used a weak validator), the response MUST NOT include other entity-headers; this prevents inconsistencies between cached entity-bodies and updated headers.
If a 304 response indicates an entity not currently cached, then the cache MUST disregard the response and repeat the request without the conditional.
If a cache uses a received 304 response to update a cache entry, the cache MUST update the entry to reflect any new field values given in the response.
10.3.6 305 Use Proxy
The requested resource MUST be accessed through the proxy given by the Location field. The Location field gives the URI of the proxy. The recipient is expected to repeat this single request via the proxy. 305 responses MUST only be generated by origin servers.
Note: RFC 2068 was not clear that 305 was intended to redirect a
single request, and to be generated by origin servers only. Not
observing these limitations has significant security consequences.
10.3.7 306 (Unused)
The 306 status code was used in a previous version of the specification, is no longer used, and the code is reserved.
10.3.8 307 Temporary Redirect
The requested resource resides temporarily under a different URI. Since the redirection MAY be altered on occasion, the client SHOULD continue to use the Request-URI for future requests. This response is only cacheable if indicated by a Cache-Control or Expires header field.
The temporary URI SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the response SHOULD contain a short hypertext note with a hyperlink to the new URI(s) , since many pre-HTTP/1.1 user agents do not understand the 307 status. Therefore, the note SHOULD contain the information necessary for a user to repeat the original request on the new URI.
If the 307 status code is received in response to a request other than GET or HEAD, the user agent MUST NOT automatically redirect the request unless it can be confirmed by the user, since this might change the conditions under which the request was issued.
10.4 Client Error 4xx
The 4xx class of status code is intended for cases in which the client seems to have erred. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. These status codes are applicable to any request method. User agents SHOULD display any included entity to the user.
If the client is sending data, a server implementation using TCP SHOULD be careful to ensure that the client acknowledges receipt of the packet(s) containing the response, before the server closes the input connection. If the client continues sending data to the server after the close, the server's TCP stack will send a reset packet to the client, which may erase the client's unacknowledged input buffers before they can be read and interpreted by the HTTP application.
10.4.1 400 Bad Request
The request could not be understood by the server due to malformed syntax. The client SHOULD NOT repeat the request without modifications.
10.4.2 401 Unauthorized
The request requires user authentication. The response MUST include a WWW-Authenticate header field (section 14.47) containing a challenge applicable to the requested resource. The client MAY repeat the request with a suitable Authorization header field (section 14.8). If the request already included Authorization credentials, then the 401 response indicates that authorization has been refused for those credentials. If the 401 response contains the same challenge as the prior response, and the user agent has already attempted authentication at least once, then the user SHOULD be presented the entity that was given in the response, since that entity might include relevant diagnostic information. HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
10.4.3 402 Payment Required
This code is reserved for future use.
10.4.4 403 Forbidden
The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated. If the request method was not HEAD and the server wishes to make public why the request has not been fulfilled, it SHOULD describe the reason for the refusal in the entity. If the server does not wish to make this information available to the client, the status code 404 (Not Found) can be used instead.
10.4.5 404 Not Found
The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address. This status code is commonly used when the server does not wish to reveal exactly why the request has been refused, or when no other response is applicable.
10.4.6 405 Method Not Allowed
The method specified in the Request-Line is not allowed for the resource identified by the Request-URI. The response MUST include an Allow header containing a list of valid methods for the requested resource.
10.4.7 406 Not Acceptable
The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
Unless it was a HEAD request, the response SHOULD include an entity containing a list of available entity characteristics and location(s) from which the user or user agent can choose the one most appropriate. The entity format is specified by the media type given in the Content-Type header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice MAY be performed automatically. However, this specification does not define any standard for such automatic selection.
Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept headers sent in the
request. In some cases, this may even be preferable to sending a
406 response. User agents are encouraged to inspect the headers of
an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD temporarily stop receipt of more data and query the user for a decision on further actions.
10.4.8 407 Proxy Authentication Required
This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy. The proxy MUST return a Proxy-Authenticate header field (section 14.33) containing a challenge applicable to the proxy for the requested resource. The client MAY repeat the request with a suitable Proxy-Authorization header field (section 14.34). HTTP access authentication is explained in "HTTP Authentication: Basic and Digest Access Authentication" [43].
10.4.9 408 Request Timeout
The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.
10.4.10 409 Conflict
The request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. The response body SHOULD include enough
information for the user to recognize the source of the conflict. Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that might not be possible and is not required.
Conflicts are most likely to occur in response to a PUT request. For example, if versioning were being used and the entity being PUT included changes to a resource which conflict with those made by an earlier (third-party) request, the server might use the 409 response to indicate that it can't complete the request. In this case, the response entity would likely contain a list of the differences between the two versions in a format defined by the response Content-Type.
10.4.11 410 Gone
The requested resource is no longer available at the server and no forwarding address is known. This condition is expected to be considered permanent. Clients with link editing capabilities SHOULD delete references to the Request-URI after user approval. If the server does not know, or has no facility to determine, whether or not the condition is permanent, the status code 404 (Not Found) SHOULD be used instead. This response is cacheable unless indicated otherwise.
The 410 response is primarily intended to assist the task of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services and for resources belonging to individuals no longer working at the server's site. It is not necessary to mark all permanently unavailable resources as "gone" or to keep the mark for any length of time -- that is left to the discretion of the server owner.
10.4.12 411 Length Required
The server refuses to accept the request without a defined Content- Length. The client MAY repeat the request if it adds a valid Content-Length header field containing the length of the message-body in the request message.
10.4.13 412 Precondition Failed
The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server. This response code allows the client to place preconditions on the current resource metainformation (header field data) and thus prevent the requested method from being applied to a resource other than the one intended.
10.4.14 413 Request Entity Too Large
The server is refusing to process a request because the request entity is larger than the server is willing or able to process. The server MAY close the connection to prevent the client from continuing the request.
If the condition is temporary, the server SHOULD include a Retry- After header field to indicate that it is temporary and after what time the client MAY try again.
10.4.15 414 Request-URI Too Long
The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret. This rare condition is only likely to occur when a client has improperly converted a POST request to a GET request with long query information, when the client has descended into a URI "black hole" of redirection (e.g., a redirected URI prefix that points to a suffix of itself), or when the server is under attack by a client attempting to exploit security holes present in some servers using fixed-length buffers for reading or manipulating the Request-URI.
10.4.16 415 Unsupported Media Type
The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
10.4.17 416 Requested Range Not Satisfiable
A server SHOULD return a response with this status code if a request included a Range request-header field (section 14.35), and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field. (For byte-ranges, this means that the first- byte-pos of all of the byte-range-spec values were greater than the current length of the selected resource.)
When this status code is returned for a byte-range request, the response SHOULD include a Content-Range entity-header field specifying the current length of the selected resource (see section 14.16). This response MUST NOT use the multipart/byteranges content- type.
10.4.18 417 Expectation Failed
The expectation given in an Expect request-header field (see section 14.20) could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.
10.5 Server Error 5xx
Response status codes beginning with the digit "5" indicate cases in which the server is aware that it has erred or is incapable of performing the request. Except when responding to a HEAD request, the server SHOULD include an entity containing an explanation of the error situation, and whether it is a temporary or permanent condition. User agents SHOULD display any included entity to the user. These response codes are applicable to any request method.
10.5.1 500 Internal Server Error
The server encountered an unexpected condition which prevented it from fulfilling the request.
10.5.2 501 Not Implemented
The server does not support the functionality required to fulfill the request. This is the appropriate response when the server does not recognize the request method and is not capable of supporting it for any resource.
10.5.3 502 Bad Gateway
The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request.
10.5.4 503 Service Unavailable
The server is currently unable to handle the request due to a temporary overloading or maintenance of the server. The implication is that this is a temporary condition which will be alleviated after some delay. If known, the length of the delay MAY be indicated in a Retry-After header. If no Retry-After is given, the client SHOULD handle the response as it would for a 500 response.
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may wish
to simply refuse the connection.
10.5.5 504 Gateway Timeout
The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access in attempting to complete the request.
Note: Note to implementors: some deployed proxies are known to
return 400 or 500 when DNS lookups time out.
10.5.6 505 HTTP Version Not Supported
The server does not support, or refuses to support, the HTTP protocol version that was used in the request message. The server is indicating that it is unable or unwilling to complete the request using the same major version as the client, as described in section 3.1, other than with this error message. The response SHOULD contain an entity describing why that version is not supported and what other protocols are supported by that server.
==========================================================
400 Invalid syntax. 语法问题
401 Access denied. 访问拒绝
402 Payment required. 必须完整
403 Request forbidden. 请求被禁止
404 Object not found. 对象没有找到
405 Method is not allowed. 方法不允许
406 No response acceptable to client found. 客户端没有响应
407 Proxy authentication required. 代理需要验证
408 Server timed out waiting for request. 等等请求时服务器断开连接
409 User should resubmit with more info. 有冲突用户应该进行检查
410 Resource is no longer available. 资源不可用
411 Server refused to accept request without a length. 服务器拒绝接受没有长度的请求
412 Precondition given in request failed. 放弃请求失败的条件
413 Request entity was too large. 请求太大
414 Request Uniform Resource Identifier (URI) too long. 请求的URI 太长
415 Unsupported media type. 不支持MEDIA类型
449 Retry after doing the appropriate action. 在作了适当动作后重试
500 Internal server error. 服务器内部错误
501 Server does not support the functionality required to fulfill the request. 服务器不支持请求的功能
502 Error response received from gateway. 从网关收到错误应答
503 Temporarily overloaded. 过载
504 Timed out waiting for gateway. 等待网关时请求断开
505 HTTP version not supported. 不支持HTTP的版本
HTTP status codes returned by servers on the Internet.
从Internet返回的HTTP status代码(HTTP 状态字)
HTTP_STATUS_CONTINUE (100)
The request can be continued.
请求不能被继续
HTTP_STATUS_SWITCH_PROTOCOLS (101)
The server has switched protocols in an upgrade header.
通过新的header服务器的协议被转换了
HTTP_STATUS_OK (200)
The request completed successfully.
请求成功的完成
HTTP_STATUS_CREATED (201)
The request has been fulfilled and resulted in the creation of a new resource.
通过新的资源请求已经被完成
HTTP_STATUS_ACCEPTED (202)
The request has been accepted for processing, but the processing has not been completed.
请求已经被接受处理，但是处理还没有完成
HTTP_STATUS_PARTIAL (203)
The returned meta information in the entity-header is not the definitive set available from the origin server.
从服务器返回的在entity-header中的meta信息是无效的
HTTP_STATUS_NO_CONTENT (204)
The server has fulfilled the request, but there is no new information to send back.
服务器实现了请求，但是没有返回信息
HTTP_STATUS_RESET_CONTENT (205)
The request has been completed, and the client program should reset the document view that caused the request to be sent to allow the user to easily initiate another input action.
请求已经被完成，并且web程序(客户端程序浏览器程序)已经重置了文档视图目录（content），这个目录很容易允许使用者用另一个动作发送请求
HTTP_STATUS_PARTIAL_CONTENT (206)
The server has fulfilled the partial GET request for the resource.
服务器已经为资源完成了部分GET请求
HTTP_STATUS_AMBIGUOUS (300)
The server couldn't decide what to return.
服务器不能判定返回什么
HTTP_STATUS_MOVED (301)
The requested resource has been assigned to a new permanent URI (Uniform Resource Identifier), and any future references to this resource should be done using one of the returned URIs.
被请求的资源已经被分配给新的URI,并且以后引用时都使用这个URIs资源。
HTTP_STATUS_REDIRECT (302)
The requested resource resides temporarily under a different URI (Uniform Resource Identifier).
请求的资源临时在不同的uri下
HTTP_STATUS_REDIRECT_METHOD (303)
The response to the request can be found under a different URI (Uniform Resource Identifier) and should be retrieved using a GET HTTP verb on that resource.
请求的资源不能在不同的uri下找到，并且从新使用GET HTTP在服务器上从新检索
HTTP_STATUS_NOT_MODIFIED (304)
The requested resource has not been modified.
请求的资源没有被改变
HTTP_STATUS_USE_PROXY (305)
The requested resource must be accessed through the proxy given by the location field.
请求的资源必须通过特定的代理获得
HTTP_STATUS_REDIRECT_KEEP_VERB (307)
The redirected request keeps the same HTTP verb. HTTP/1.1 behavior.
从定位请求，
HTTP_STATUS_BAD_REQUEST (400)
The request could not be processed by the server due to invalid syntax.
因为语法不能被服务器处理
HTTP_STATUS_DENIED (401)
The requested resource requires user authentication.
请求资源命令必须被验证（拒绝访问）
HTTP_STATUS_PAYMENT_REQ (402)
Not currently implemented in the HTTP protocol.
没有完全实现HTTP协议
HTTP_STATUS_FORBIDDEN (403)
The server understood the request, but is refusing to fulfill it.
服务器理解了请求，但是拒绝完成他
HTTP_STATUS_NOT_FOUND (404)
The server has not found anything matching the requested URI (Uniform Resource Identifier).
没有找到任何被指定的URI
HTTP_STATUS_BAD_METHOD (405)
The HTTP verb used is not allowed.
Http动作不被允许
HTTP_STATUS_NONE_ACCEPTABLE (406)
No responses acceptable to the client were found.
应答没有被客户接受
HTTP_STATUS_PROXY_AUTH_REQ (407)
Proxy authentication required.
代理必须被验证
HTTP_STATUS_REQUEST_TIMEOUT (408)
The server timed out waiting for the request.
服务器在等待请求时中止了
HTTP_STATUS_CONFLICT (409)
The request could not be completed due to a conflict with the current state of the resource. The user should resubmit with more information.
请求不能被完成，问题是资源冲突。用户应该进行调整
HTTP_STATUS_GONE (410)
The requested resource is no longer available at the server, and no forwarding address is known.
请求的资源在服务器上不再可用，而且没有转发地址
HTTP_STATUS_LENGTH_REQUIRED (411)
The server refuses to accept the request without a defined content length.
服务器拒绝接受没有定义目录大小的请求
HTTP_STATUS_PRECOND_FAILED (412)
The precondition given in one or more of the request header fields evaluated to false when it was tested on the server.
当在服务器上测试请求头文件放弃一个或者多个请求的条件
HTTP_STATUS_REQUEST_TOO_LARGE (413)
The server is refusing to process a request because the request entity is larger than the server is willing or able to process.
服务器拒绝处理请求，原因是请求的大小超过服务器能够处理的大小
HTTP_STATUS_URI_TOO_LONG (414)
The server is refusing to service the request because the request URI (Uniform Resource Identifier) is longer than the server is willing to interpret.
服务器拒绝服务，原因是请求的URI超过了服务器能够揭示的长度
HTTP_STATUS_UNSUPPORTED_MEDIA (415)
The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
服务器拒绝服务，原因是请求格式不被支持
HTTP_STATUS_RETRY_WITH (449)
The request should be retried after doing the appropriate action.
在作了适当的动作后请求被重试
HTTP_STATUS_SERVER_ERROR (500)
The server encountered an unexpected condition that prevented it from fulfilling the request.
服务器遇到请求失败意外
HTTP_STATUS_NOT_SUPPORTED (501)
The server does not support the functionality required to fulfill the request.
服务器不支持必须完成请求的功能
HTTP_STATUS_BAD_GATEWAY (502)
The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request.
服务器当作为网关或代理时，从上行服务器接受的响应请求失败
HTTP_STATUS_SERVICE_UNAVAIL (503)
The service is temporarily overloaded.
【服务器暂时被block】
服务器负载
HTTP_STATUS_GATEWAY_TIMEOUT (504)
The request was timed out waiting for a gateway.
等待网关时请求断开，没有响应
HTTP_STATUS_VERSION_NOT_SUP (505)
The server does not support, or refuses to support, the HTTP protocol version that was used in the request message.
服务器不支持或者拒绝支持正在使用请求的HTTP协议的版本
我的异常网推荐解决方案：The server encountered an internal error () that prevented it from fulfilling this request.,http://www.myexception.cn/java-web/317.html