2.9. 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)   ...  ...   

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.

2.9.1. 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.

2.9.2. 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 