Servlet HTTP status code

May 14, 2021 Servlet

2. The method by which the HTTP status code is set

Servlet HTTP status code

HTTP requests and HTTP response messages are in a similar format, structured as follows:

Initial status line and carriage return line break (carriage return plus line break)
Zero or more header lines plus carriage breaks
A blank line, the carriage return line break
An optional message body, such as a file, query data, or query output

For example, the server's response header looks like this:

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

The status lines include 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	information	describe
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 is successful.
201	Created	This request is complete and creates a new resource.
202	Accepted	This request is accepted, but this processing is incomplete.
203	Non-authoritative Information
204	No Content
205	Reset Content
206	Partial Content
300	Multiple Choices	Link list.Users can choose a link to enter this location.Up to five addresses.
301	Moved Permanently	The requested page has been transferred to a new URL.
302	Found	The requested page is temporarily transferred to a new URL.
303	See Other	The requested page can be found under another different URL.
304	Not Modified
305	Use Proxy
306	Unused	Use this code in previous versions.It is no longer used now, but the code is still retained.
307	Temporary Redirect	The requested page is temporarily transferred 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 can't use this code.
403	Forbidden	It is forbidden to access 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 only generates a response that is not accepted by the client.
407	Proxy Authentication Required	Before requesting delivery, you must use the proxy server verification.
408	Request Timeout	The time requested is longer than the server waiting for the server, timeout.
409	Conflict	Requests cannot be completed because of conflict.
410	Gone	The requested page is no longer available.
411	Length Required	"Content-Length" is not defined.The server cannot process request information that does not have Content-Length.
412	Precondition Failed	The prerequisites given in the request are evaluated by the server to false.
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.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	Unfinished request.The server encountered an unexpected situation.
501	Not Implemented	Unfinished request.The server does not support the required features.
502	Bad Gateway	Unfinished request.The server receives an invalid response from the upstream server.
503	Service Unavailable	Unfinished request.The server is temporarily overloaded or dead.
504	Gateway Timeout	Gateway timeout.
505	HTTP Version Not Supported	The server does not support the "HTTP Protocol" version.

The method by which the HTTP status code is set

The following methods can be used to set the HTTP status code in a servlet program. These methods are available through the HttpServletResponse object.

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 reaction contains a special status code and document, make sure you are using PrintWriter Call SetStatus before returning anything.
2	public void sendRedirect(String url) This method generates a 302 response, along with a new document URL Location head.
3	public void sendError(int code, String message) This method sends a status code (usually 404), together with a short message to the client in the HTML document, and sends it to the client.

HTTP status code instance

The following example sends a 407 error code to the client browser, which displays a "Need !!!" message.

// 导入必需的 java 库
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

// 扩展 HttpServlet 类
public class showError extends HttpServlet {
 
  // 处理 GET 方法请求的方法
  public void doGet(HttpServletRequest request,
                    HttpServletResponse response)
            throws ServletException, IOException
  {
      // 设置错误代码和原因
      response.sendError(407, "Need authentication!!!" );
  }
  // 处理 POST 方法请求的方法
  public void doPost(HttpServletRequest request,
                     HttpServletResponse response)
      throws ServletException, IOException {
     doGet(request, response);
  }
}

The call to the servlet above now shows the following results:

HTTP Status 407 - Need authentication!!!

type Status report

message Need authentication!!!

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

Servlet HTTP status code

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