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The format of HTTP requests and HTTP responses is similar, with the following structure:
Followed by the status line+Starts with CRLF (carriage return line feed)
Zero or more lines of header modules+CRLF
A blank line, such as CRLF
Optional message bodies such as files, query data, and query output
For example, a server response header looks like the following:
HTTP/1.1 200 OK Content-Type: .../html Header2: ... ... HeaderN: ... (Blank Line) <!doctype ...> <html> <head>.../head> <body> ... </body> </html>
The status line contains the HTTP version, a status code, and a short message corresponding to the status code.
The following table lists the HTTP status codes that may be returned by the server and the associated messages:
| Status 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 by the server, the client will continue this request |
| 101 | Switching Protocols | Server Switching Protocol |
| 200 | OK | The request has been confirmed |
| 201 | Created | The request was complete, and a new resource was created |
| 202 | Accepted | The request has been accepted but not yet processed |
| 203 | Non-authoritative Information | |
| 204 | No Content | |
| 205 | Reset Content | |
| 206 | Partial Content | |
| 300 | Multiple Choices | A hyperlinks table, where users can select a hyperlinks and access, with a maximum support of5hyperlinks |
| 301 | Moved Permanently | The requested page has been moved to a new URL |
| 302 | Found | The requested page has temporarily moved to a new URL |
| 303 | See Other | The requested page can be found at a different URL |
| 304 | Not Modified | |
| 305 | Use Proxy | |
| 306 | Unused | This status code is no longer in use, but the status code is retained |
| 307 | Temporary Redirect | The requested page has temporarily moved to a new URL |
| 400 | Bad Request | The server cannot recognize the request |
| 401 | Unauthorized | The requested page requires a username and password |
| 402 | Payment Required | This status code cannot be used at present |
| 403 | Forbidden | Access to the requested page is prohibited |
| 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 can only create a response that the client cannot accept |
| 407 | Proxy Authentication Required | A proxy server must be authenticated before the request is served |
| 408 | Request Timeout | The request time exceeded the time the server can wait, and the connection was disconnected |
| 409 | Conflict | The request has contradictions |
| 410 | Gone | The requested page is no longer available |
| 411 | Length Required | "Content-Length" is not defined, the server refuses to accept the request |
| 412 | Precondition Failed | The request's preconditions were evaluated as false by the server |
| 413 | Request Entity Too Large | The server refuses to accept the request because the request entity is too large |
| 414 | Request-url Too Long | The server refuses to accept the request because the URL is too long. It often appears when a large amount of query information is attached to the 'POST' request converted to a 'GET' request |
| 415 | Unsupported Media Type | The server refuses to accept the request because the media type is not supported |
| 417 | Expectation Failed | |
| 500 | Internal Server Error | The request is incomplete, the server encountered an unexpected situation |
| 501 | Not Implemented | The request is incomplete, the server does not provide the required functionality |
| 502 | Bad Gateway | The request is incomplete, the server received an invalid response from the upstream server |
| 503 | Service Unavailable | The request is incomplete, the server is temporarily restarting or shutting down |
| 504 | Gateway Timeout | Gateway Timeout |
| 505 | HTTP Version Not Supported | The server does not support the specified HTTP version |
The following table lists the methods used in HttpServletResponse class to set status codes:
| S.N. | Method & Description |
|---|---|
| 1 | public void setStatus ( int statusCode ) This method can set any status code. If your response contains a special status code and a document, make sure to call the setStatus method before returning any content with PrintWriter |
| 2 | public void sendRedirect(String url) This method produces302response, and at the same time produces a Location header tells the URL a new document |
| 3 | public void sendError(int code, String message) This method takes a status code (usually 404) and a short message, automatically inserted into the HTML document and sent back to the client |
The following example will send407Error code to the browser, and then the browser will tell you "Need authentication!!!".
<html> <head> <title>Setting HTTP Status Code</title> </head> <body> <% // Set the error code and explain the reason response.sendError(407, "Need authentication!!!"); %> </body> </html>
Accessing the above JSP page will result in the following:
You can also try using other status codes to see if you get any unexpected results.