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The format of an HTTP request and HTTP response is similar, both having the following structure: * Starts with a status line + CRLF (Carriage Return Line Feed) * Zero or more header lines + CRLF * A blank line, i.e., CRLF * An optional message body, such as a file, query data, or query output For example, a server response header looks like this: HTTP/1.1 200 OK Content-Type: text/html Header2: ......HeaderN: ... (Blank Line)...... The status line contains the HTTP version, a status code, and a short message corresponding to the status code. The following table lists the HTTP status codes that may be returned from the server and their associated messages: | **Status Code** | **Message** | **Description** | | --- | --- | --- | | 100 | Continue | Only part of the request has been received by the server, but the client should continue with the request as long as it hasn't been rejected by the server. | | 101 | Switching Protocols | The server is switching protocols. | | 200 | OK | The request is confirmed. | | 201 | Created | The request is complete, and a new resource is created. | | 202 | Accepted | The request has been accepted for processing, but the processing has not been completed. | | 203 | Non-authoritative Information | | | 204 | No Content | | | 205 | Reset Content | | | 206 | Partial Content | | | 300 | Multiple Choices | A list of hyperlinks, the user can select one hyperlink to visit. Supports up to 5 hyperlinks. | | 301 | Moved Permanently | The requested page has been moved to a new URL. | | 302 | Found | The requested page has been temporarily moved to a new URL. | | 303 | See Other | The requested page can be found under a different URL. | | 304 | Not Modified | | | 305 | Use Proxy | | | 306 | _Unused_ | This status code is no longer used, but it is reserved. | | 307 | Temporary Redirect | The requested page has been temporarily moved to a new URL. | | 400 | Bad Request | The server cannot understand the request. | | 401 | Unauthorized | The requested page requires a username and password. | | 402 | Payment Required | _This status code is not yet in use._ | | 403 | Forbidden | Access to the requested page is forbidden. | | 404 | Not Found | The server cannot find the requested page. | | 405 | Method Not Allowed | The method specified in the request is not allowed. | | 406 | Not Acceptable | The server can only generate a response that the client cannot accept. | | 407 | Proxy Authentication Required | Authentication with a proxy server is required before the request can be served. | | 408 | Request Timeout | The request took longer than the server was prepared to wait, and the connection was closed. | | 409 | Conflict | The request could not be completed due to a conflict. | | 410 | Gone | The requested page is no longer available. | | 411 | Length Required | "Content-Length" is not defined, and the server refuses to accept the request. | | 412 | Precondition Failed | The precondition given in the request evaluated to false by the server. | | 413 | Request Entity Too Large | The server refuses to accept the request because the request entity is too large. | | 414 | Request-url Too Long | The server refuses to accept the request because the URL is too long. This often occurs when a "POST" request is converted to a "GET" request with a long query information. | | 415 | Unsupported Media Type | The server refuses to accept the request because the media type is not supported. | | 417 | Expectation Failed | | | 500 | Internal Server Error | The request was incomplete, and the server encountered an unexpected condition. | | 501 | Not Implemented | The request was incomplete, and the server does not support the functionality required to fulfill the request. | | 502 | Bad Gateway | The request was incomplete, and the server received an invalid response from the upstream server. | | 503 | Service Unavailable | The request was incomplete, and the server is temporarily restarting or shutting down. | | 504 | Gateway Timeout | The gateway timed out. | | 505 | HTTP Version Not Supported | The server does not support the HTTP version specified in the request. | * * * ## Methods for Setting HTTP Status Codes The following table lists the methods in the HttpServletResponse class used to set status codes: | **S.N.** | **Method & Description** | | --- | --- | | 1 | **public void setStatus ( int statusCode )** This method can set any status code. If your response contains a specific status code and a document, make sure to call the setStatus method before returning any content with PrintWriter. | | 2 | **public void sendRedirect(String url)** This method generates a 302 response along with a _Location_ header telling the URL of a new document. | | 3 | **public void sendError(int code, String message)** This method sends a status code (usually 404) and a short message, automatically inserting them into an HTML document and sending it back to the client. | * * * ## HTTP Status Code Program Example The following example will send a 407 error code to the browser, and the browser will tell you "Need authentication!!!". Accessing the above JSP page will yield the following result:  You can also try using other status codes to see if you get any unexpected results.