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Monday, January 23, 2017

Servlets - Http Status Codes

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 ie. New Line )
  • Zero or more header lines + CRLF
  • A blank line ie. a CRLF
  • An optioanl 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.
400Bad 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. 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  
500Internal 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:

There are following methods which can be used to set HTTP Status Code in your servlet program. These methods are available with HttpServletResponse object.
S.N.Method & Description
1public 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.
2public void sendRedirect(String url)
This method generates a 302 response along with a Location header giving the URL of the new document.
3public 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 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 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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