📅  最后修改于: 2020-11-13 05:19:43             🧑  作者: Mango
在本章中,我们将讨论JSP中的服务器响应。当Web服务器响应HTTP请求时,响应通常包括状态行,某些响应标头,空白行和文档。一个典型的响应看起来像这样-
HTTP/1.1 200 OK
Content-Type: text/html
Header2: ...
...
HeaderN: ...
(Blank Line)
..>
...
...
状态行由HTTP版本(示例中为HTTP / 1.1) ,状态代码(示例中为200)以及与状态代码相对应的非常短的消息(示例中为OK)组成。
以下是最有用的HTTP 1.1响应标头的摘要,这些标头从Web服务器返回到浏览器。这些标头经常在Web编程中使用-
S.No. | Header & Description |
---|---|
1 |
Allow This header specifies the request methods (GET, POST, etc.) that the server supports. |
2 |
Cache-Control This header specifies the circumstances in which the response document can safely be cached. It can have values public, private or no-cache etc. Public means document is cacheable, Private means document is for a single user and can only be stored in private (nonshared) caches and no-cache means document should never be cached. |
3 |
Connection This header instructs the browser whether to use persistent HTTP connections or not. A value of close instructs the browser not to use persistent HTTP connections and keep-alive means using persistent connections. |
4 |
Content-Disposition This header lets you request that the browser ask the user to save the response to disk in a file of the given name. |
5 |
Content-Encoding This header specifies the way in which the page was encoded during transmission. |
6 |
Content-Language This header signifies the language in which the document is written. For example, en, en-us, ru, etc. |
7 |
Content-Length This header indicates the number of bytes in the response. This information is needed only if the browser is using a persistent (keep-alive) HTTP connection. |
8 |
Content-Type This header gives the MIME (Multipurpose Internet Mail Extension) type of the response document. |
9 |
Expires This header specifies the time at which the content should be considered out-of-date and thus no longer be cached. |
10 |
Last-Modified This header indicates when the document was last changed. The client can then cache the document and supply a date by an If-Modified-Since request header in later requests. |
11 |
Location This header should be included with all responses that have a status code in the 300s. This notifies the browser of the document address. The browser automatically reconnects to this location and retrieves the new document. |
12 |
Refresh This header specifies how soon the browser should ask for an updated page. You can specify time in number of seconds after which a page would be refreshed. |
13 |
Retry-After This header can be used in conjunction with a 503 (Service Unavailable) response to tell the client how soon it can repeat its request. |
14 |
Set-Cookie This header specifies a cookie associated with the page. |
响应对象是javax.servlet.http.HttpServletResponse对象的实例。正如服务器创建请求对象一样,它也创建一个对象来表示对客户端的响应。
响应对象还定义了用于处理创建新HTTP标头的接口。通过此对象,JSP程序员可以添加新的cookie或日期戳,HTTP状态代码等。
可以使用以下方法在servlet程序中设置HTTP响应标头。这些方法可用于HttpServletResponse对象。该对象代表服务器响应。
S.No. | Method & Description |
---|---|
1 |
String encodeRedirectURL(String url) Encodes the specified URL for use in the sendRedirect method or, if encoding is not needed, returns the URL unchanged. |
2 |
String encodeURL(String url) Encodes the specified URL by including the session ID in it, or, if encoding is not needed, returns the URL unchanged. |
3 |
boolean containsHeader(String name) Returns a boolean indicating whether the named response header has already been set. |
4 |
boolean isCommitted() Returns a boolean indicating if the response has been committed. |
5 |
void addCookie(Cookie cookie) Adds the specified cookie to the response. |
6 |
void addDateHeader(String name, long date) Adds a response header with the given name and date-value. |
7 |
void addHeader(String name, String value) Adds a response header with the given name and value. |
8 |
void addIntHeader(String name, int value) Adds a response header with the given name and integer value. |
9 |
void flushBuffer() Forces any content in the buffer to be written to the client. |
10 |
void reset() Clears any data that exists in the buffer as well as the status code and headers. |
11 |
void resetBuffer() Clears the content of the underlying buffer in the response without clearing headers or status code. |
12 |
void sendError(int sc) Sends an error response to the client using the specified status code and clearing the buffer. |
13 |
void sendError(int sc, String msg) Sends an error response to the client using the specified status. |
14 |
void sendRedirect(String location) Sends a temporary redirect response to the client using the specified redirect location URL. |
15 |
void setBufferSize(int size) Sets the preferred buffer size for the body of the response. |
16 |
void setCharacterEncoding(String charset) Sets the character encoding (MIME charset) of the response being sent to the client, for example, to UTF-8. |
17 |
void setContentLength(int len) Sets the length of the content body in the response In HTTP servlets; this method also sets the HTTP Content-Length header. |
18 |
void setContentType(String type) Sets the content type of the response being sent to the client, if the response has not been committed yet. |
19 |
void setDateHeader(String name, long date) Sets a response header with the given name and date-value. |
20 |
void setHeader(String name, String value) Sets a response header with the given name and value. |
21 |
void setIntHeader(String name, int value) Sets a response header with the given name and integer value. |
22 |
void setLocale(Locale loc) Sets the locale of the response, if the response has not been committed yet. |
23 |
void setStatus(int sc) Sets the status code for this response. |
以下示例将使用setIntHeader()方法设置Refresh标头以模拟数字时钟-
Auto Refresh Header Example
Auto Refresh Header Example
现在将上面的代码放在main.jsp中,并尝试访问它。每隔5秒将显示当前系统时间,如下所示。运行JSP。您将收到以下输出:-
Auto Refresh Header Example
Current Time is: 9:44:50 PM
您可以尝试以类似方式尝试其他方法。