In the HTTP response message, in addition to the message body is what we need to focus on, but also need to focus on a very important field, which is the status field, also known as the status code.
HTTP status response status code is divided into five categories:
1xx: Informational status code
2xx: Success status code
200：OK
201：created
3xx: Redirection status code
301: Permanently Moved (permanent transfer); the use of headers in the response message "Location: URL"; specify the location where the resources are now
302: Fonud (temporary redirect); the use of headers in the response message "Location: URL"; specify a temporary resource position
304: Not Modified (you can use the cache); tell the client does not change the resource; conditional expressions used in the request
4xx: Client Error message
403: Forbidden; server request is denied
404: Not Found; server can not find the requested URL
405: Method Not Allowed; allowed to use this method corresponding to the request URL
5xx: server-side error message
500: Internal Server Error; internal server error
502: Bad Gateway; proxy server receives a response from the upper dummy
503: Service Unavailable; server at this time can not provide services; but in the future may be available
Reproduced in: https: //www.jianshu.com/p/dd157855cd76