Servlet HTTP status code

The format of the HTTP request and HTTP response message is similar, and thestructure is as follows:

Initial status line + carriage return newline character (carriage return + line feed)
Zero or more header lines + carriage return newline character
A blank line, that is, the enter newline character
An optional message body, such as a file, query data, or query output

For example, the response header for the server is 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 includes the HTTP version (HTTP/1.1 in this case), a status code (200 in this case), and a short message corresponding to the status code (OK in this case).

The following is a list of HTTP status codes and related information that may be returned from the Web server:

Code	Message	Description
100	`Continue`	Only part of the request has been received by the server, but as long as it is not rejected, the client should continue the request.
101	`Switching Protocols`	Server switching protocol.
200	`OK`	The request was successful.
201	`Created`	The request is complete and a new resource is created.
202	`Accepted`	The request is accepted, but the processing is incomplete.
203	`Non-authoritative Information`
204	`No Content`
205	`Reset Content`
206	`Partial Content`
300	`Multiple Choices`	Link list. The user can select a link to go to that location. Five addressesat the most.
301	`Moved Permanently`	The requested page has been transferred to a new URL.
302	`Found`	The requested page has been temporarily transferred 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 previous versions. It is no longer used, but the code is still retained.
307	`Temporary Redirect`	The requested page has been temporarily transferred to a new URL.
400	`Bad Request`	The server does not understand the request.
401	`Unauthorized`	The requested page requires a user name and password.
402	`Payment Required`	You cannot use this code yet.
403	`Forbidden`	Access to the requested page is prohibited.
404	`Not Found`	The server could not find the requested page. .
405	`Method Not Allowed`	The method specified in the request is not allowed.
406	`Not Acceptable`	The server generates only one response that is not accepted by the client.
407	`Proxy Authentication Required`	You must use the authentication of the proxy server before the request can be delivered.
408	`Request Timeout`	The request takes longer than the server can wait and times out.
409	`Conflict`	The request could not be completed because of a conflict.
410	`Gone`	The requested page is no longer available.
411	`Length Required`	“Content-Length” is not defined. The server cannot process the request information sent by the client without Content-Length.
412	`Precondition Failed`	The prerequisites given in the request are evaluated as false by the server.
413	`Request Entity Too Large`	The server does not accept the request because the request entity is too large.
414	`Request-url Too Long`	The server does not accept the request because the URL is too long. Occurs when you convert a “post” request to a “get” request with long query information.
415	`Unsupported Media Type`	The server does not accept the request because the media type is not supported.
417	`Expectation Failed`
500	`Internal Server Error`	Outstanding request. The server encountered an unexpected condition.
501	`Not Implemented`	Outstanding request. The server does not support the required functionality.
502	`Bad Gateway`	Outstanding request. The server received an invalid response from the upstream server.
503	`Service Unavailable`	Outstanding request. The server is temporarily overloaded or crashed.
504	`Gateway Timeout`	The gateway timed out.
505	`HTTP Version Not Supported`	The server does not support the HTTP Protocol version.

The method of setting HTTP status code

The following method can be used to set the HTTP status code in a Servlet program. These methods are passed through HttpServletResponse Object isavailable.

Serial number	Method & description
1	`public void setStatus ( int statusCode )` this method sets an arbitrary status code. The setStatus method takes an int (status code) as a parameter.If your response contains a special status code and documentation, be sure to call setStatus before using PrintWriter to actually return anything.
2	`public void sendRedirect(String url)` this method generates a 302 response, along with a Location header with the new document URL.
3	`public void sendError(int code, String message)` this method sends a status code (usually 404), together with a short message that is automatically formatted within the HTML document and sent to the client.

HTTP status code example

The following example sends the 407 error code to the client browser, which displays “Need authenticating error codes!” News.

// Import necessary Java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import javax.servlet.annotation.WebServlet;

@WebServlet("/showError")
// Extend HttpServlet Class
public class showError extends HttpServlet {

  // Method for handling GET method requests
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // Set error codes and reasons
      response.sendError(407, "Need authentication!!!" );
  }
  // Method for handling POST method requests
  public void doPost(HttpServletRequest request,
                     HttpServletResponse response)
      throws ServletException, IOException {
     doGet(request, response);
  }
}

Now, calling the above Servlet will display the following result:

HTTP Status 407 - Need authentication!!!
type Status report

message Need authentication!!!

description The client must first authenticate itself with the proxy (Need authentication!!!).

Apache Tomcat/5.5.29

The method of setting HTTP status code
HTTP status code example