Servlet Writing Filters Servlet Server HTTP Response

Servlet HTTP Status Codes

The format of HTTP request and HTTP response messages is similar, with the following structure:

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

For example, the server response headers are as follows:

HTTP/1.1　200 OK
Content-Type: .../html
Header2: ...
...
HeaderN: ...
　　(Blank Line)
<!doctype ...>
<html>
<head>.../head>
<body>
...
</body>
</html>

The status line includes the HTTP version (in this example, HTTP/1.1), a status code (in this example, 200) and a short message corresponding to the status code (in this example, OK).

The following is a list of possible HTTP status codes returned by web servers and the related information:

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 protocols.
200	OK	Request successful.
201	Created	This request is complete and creates a new resource.
202	Accepted	The request is accepted and processed, but the processing is incomplete.
203	Non-authoritative Information
204	No Content
205	Reset Content
206	Partial Content
300	Multiple Choices	List of links. The user can choose a link to enter the location. Up to five addresses.
301	Moved Permanently	The requested page has been moved to a new URL.
302	Found	The requested page has been temporarily redirected to a new URL.
303	See Other	The requested page can be found at another different URL.
304	Not Modified
305	Use Proxy
306	Unused	This code was used in previous versions. It is no longer used now, but the code is still retained.
307	Temporary Redirect	The requested page has been temporarily redirected to a new URL.
400	Bad Request	The server does not understand the request.
401	Unauthorized	The requested page requires a username and password.
402	Payment Required	You are not yet able to use this code.
403	Forbidden	Access to the requested page is forbidden.
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 only generates a response that is not accepted by the client.
407	Proxy Authentication Required	You must use the proxy server's authentication before the request is delivered.
408	Request Timeout	The request needs more time than the server can wait, resulting in a timeout.
409	Conflict	The request could not be completed due to a conflict.
410	Gone	The requested page is no longer available.
411	Length Required	"Content"-"Length" is undefined. The server cannot process the client's request without Content.-Length of the request information.
412	Precondition Failed	The prerequisite provided in the request is 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. This 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	Incomplete request. The server encountered an unexpected situation.
501	Not Implemented	Incomplete request. The server does not support the required function.
502	Bad Gateway	Incomplete request. The server received an invalid response from the upstream server.
503	Service Unavailable	Incomplete request. The server is temporarily overloaded or has crashed.
504	Service Unavailable	Gateway Timeout
505	HTTP Version Not Supported	The server does not support the "HTTP protocol" version.

Methods to set HTTP status codes

The following methods can be used to set HTTP status codes in servlet programs. These methods are set through HttpServletResponse Object available.

Serial number	Method & Description
1	public void setStatus ( int statusCode ) This method sets an arbitrary status code. The setStatus method accepts an int (status code) as a parameter. If your response contains a special status code and document, make sure to use PrintWriter call setStatus before returning any content actually.
2	public void sendRedirect(String url) This method generates a 302 response, along with a new document URL Location header.
3	public void sendError(int code, String message) This method sends a status code (usually 404），along with a short message formatted and sent to the client automatically within the HTML document.

HTTP status code examples

The following example takes 407 Error codes are sent to the client browser, and the browser will display the message "Need authentication!!!".

//　Import the necessary java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
import javax.servlet.annotation.WebServlet;
@WebServlet("/showError())
//　Extend the HttpServlet class
public class showError extends HttpServlet {}}
　
　　//　Method to handle GET method requests
　　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 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

Servlet Writing Filters Servlet Server HTTP Response

Servlet Tutorial

Servlet HTTP Status Codes

Methods to set HTTP status codes

HTTP status code examples

HTTP Status 407 - Need authentication!!!

Apache Tomcat/5.5.29