In this chapter, we will discuss the Http Status Codes in JSP. The format of the HTTP request and the HTTP response messages are similar and will have the following structure −
An initial status line + CRLF (Carriage Return + Line Feed ie. New Line)
Zero or more header lines + CRLF
A blank line ie. a CRLF
An optional message body like file, query data or query output.
For example, a server response header looks like the following −
HTTP/1.1 200 OK Content-Type: text/html Header2: ... ... HeaderN: ... (Blank Line) <!doctype ...> <html> <head>...</head> <body> ... </body> </html>
The status line consists of the HTTP version (HTTP/1.1 in the example), a status code (200 in the example), and a very short message corresponding to the status code (OK in the example).
Following table lists out the HTTP status codes and associated messages that might be returned from the Web Server −
|100||Continue||Only a part of the request has been received by the server, but as long as it has not been rejected, the client should continue with the request|
|101||Switching Protocols||The server switches protocol.|
|200||OK||The request is OK|
|201||Created||The request is complete, and a new resource is created|
|202||Accepted||The request is accepted for processing, but the processing is not complete.|
|300||Multiple Choices||A link list; the user can select a link and go to that location. Maximum five addresses.|
|301||Moved Permanently||The requested page has moved to a new url.|
|302||Found||The requested page has moved temporarily to a new url.|
|303||See Other||The requested page can be found under a different url.|
|306||Unused||This code was used in a previous version. It is no longer used, but the code is reserved.|
|307||Temporary Redirect||The requested page has moved temporarily to a new url.|
|400||Bad Request||The server did not understand the request.|
|401||Unauthorized||The requested page needs a username and a password.|
|402||Payment Required||You can not use this code yet.|
|403||Forbidden||Access is forbidden to the requested page|
|404||Not Found||The server can not 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 is not accepted by the client.|
|407||Proxy Authentication Required||You must authenticate with a proxy server before this request can be served.|
|408||Request Timeout||The request took longer than the server was prepared to wait.|
|409||Conflict||The request could not be completed because of a conflict.|
|410||Gone||The requested page is no longer available.|
|411||Length Required||The "Content-Length" is not defined. The server will not accept the request without it.|
|412||Precondition Failed||The precondition given in the request evaluated to false by the server.|
|413||Request Entity Too Large||The server will not accept the request, because the request entity is too large.|
|414||Request-url Too Long||The server will not accept the request, because the url is too long. This occurs when you convert a "post" request to a "get" request with a long query information.|
|415||Unsupported Media Type||The server will not accept the request, because the media type is not supported.|
|500||Internal Server Error||The request was not completed. The server met an unexpected condition.|
|501||Not Implemented||The request was not completed. The server did not support the functionality required.|
|502||Bad Gateway||The request was not completed. The server received an invalid response from the upstream server.|
|503||Service Unavailable||The request was not completed. The server is temporarily overloading or down.|
|504||Gateway Timeout||The gateway has timed out.|
|505||HTTP Version Not Supported||The server does not support the "http protocol" version.|
Following methods can be used to set the HTTP Status Code in your servlet program. These methods are available with the HttpServletResponse object.
|S.No.||Method & Description|
public void setStatus ( int statusCode )
This method sets an arbitrary status code. The setStatus method takes an int (the status code) as an argument. If your response includes a special status code and a document, be sure to call setStatus before actually returning any of the content with the PrintWriter.
public void sendRedirect(String url)
This method generates a 302 response along with a Location header giving the URL of the new document.
public void sendError(int code, String message)
This method sends a status code (usually 404) along with a short message that is automatically formatted inside an HTML document and sent to the client.
Following example shows how a 407 error code is sent to the client browser. After this, the browser would show you "Need authentication!!!" message.
<html> <head> <title>Setting HTTP Status Code</title> </head> <body> <% // Set error code and reason. response.sendError(407, "Need authentication!!!" ); %> </body> </html>
You will receive the following output −
HTTP Status 407 - Need authentication!!!
type Status report
message Need authentication!!!
description The client must first authenticate itself with the proxy (Need authentication!!!).
To become more comfortable with HTTP status codes, try to set different status codes and their description.