”;
The format of the HTTP request and HTTP response messages are similar and will have following structure −
-
An initial status line + CRLF ( Carriage Return + Line Feed i.e. New Line )
-
Zero or more header lines + CRLF
-
A blank line, i.e., a CRLF
-
An optional message body like file, query data or query output.
For example, a server response header looks as follows −
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 is a list of HTTP status codes and associated messages that might be returned from the Web Server −
| Code | Message | Description |
|---|---|---|
| 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. |
| 203 | Non-authoritative Information | |
| 204 | No Content | |
| 205 | Reset Content | |
| 206 | Partial Content | |
| 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 |
| 304 | Not Modified | |
| 305 | Use Proxy | |
| 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 cannot use this code yet |
| 403 | Forbidden | Access is forbidden to the requested page |
| 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 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. 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. |
| 417 | Expectation Failed | |
| 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. |
Methods to Set HTTP Status Code
The following methods can be used to set HTTP Status Code in your servlet program. These methods are available with HttpServletResponse object.
| Sr.No. | Method & Description |
|---|---|
| 1 |
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. |
| 2 |
public void sendRedirect(String url) This method generates a 302 response along with a Location header giving the URL of the new document |
| 3 |
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. |
HTTP Status Code Example
Following is the example which would send a 407 error code to the client browser and browser would show you “Need authentication!!!” message.
// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
// Extend HttpServlet class
public class showError extends HttpServlet {
// Method to handle GET method request.
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// Set error code and reason.
response.sendError(407, "Need authentication!!!" );
}
// Method to handle POST method request.
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
Now calling the above servlet would display the following result −
HTTP Status 407 - Need authentication!!!
type Status report
messageNeed authentication!!!
descriptionThe client must first authenticate itself with the proxy (Need authentication!!!).
Apache Tomcat/5.5.29
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