Response codes are always three digit numbers that are divided into groups. Each group has a meaning as shown below:
lxx: Informational: Request received, continuing process.
2xx: Success: The action was successfully received, understood, and accepted.
3xx: Redirection: Further action must be taken in order to complete the request.
4xx: User—Agent Error: The request contains bad syntax or cannot be fulﬁlled.
5XX: Server Error: The server failed to fulﬁll an apparently valid request.
Each Status: Code has an associated string (reason phrase).
The status code you’ll see most often is 200. This means that everything has succeeded and you have a valid response. The others you are likely to see are:
401: you are not authorized to make this request
404: cannot ﬁnd the requested URI
405: the HTTP method you have tried to execute is not sup» ported by this URL (e.g., you have sent a POST and the URL will only accept GET)
500: Internal Server Error. You are likely to see this if there source to where you are browsing (such as a Servlet) throws
Suppose as a developer you get error code of 500, to discover the root cause of this exception you should check the application output log