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response (2)

💻 Programming/JSP

[JSP] Response Object ( Server Response, Auto Refresh )

Web server가 HTTP request에 대한 응답을 브라우저에 보낼때 그 응답은 전형적으로 상태정보와 몇몇 응답 헤더들 그리고 빈 줄 그리고 문서로 이루어져 있다. 보통 아래처럼 응답이 구성된다.

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

상태정보를 표시하는 첫번째 줄은 HTTP 버전 (위 예제에서는 HTTP/1.1 ), 상태코드 ( 위 예제에서는 200 ), 그리고 상태코드에 맞는 짧은 메시지 (위 예에서는 OK )로 구성됩니다.

아래 테이블의 내용은 HTTP 1.1 응답헤더의 유용한 정보들입니다.

Header	Description
Allow	This header specifies the request methods (GET, POST, etc.) that the server supports.
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.
Connection	This header instructs the browser whether to use persistent in HTTP connections or not. A value of close instructs the browser not to use persistent HTTP connections and keep-alive means using persistent connections.
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.
Content-Encoding	This header specifies the way in which the page was encoded during transmission.
Content-Language	This header signifies the language in which the document is written. For example en, en-us, ru, etc.
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.
Content-Type	This header gives the MIME (Multipurpose Internet Mail Extension) type of the response document.
Expires	This header specifies the time at which the content should be considered out-of-date and thus no longer be cached.
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.
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.
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.
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.
Set-Cookie	This header specifies a cookie associated with the page.

HttpServletResponse

HttpServletResponse 객체에서 제공하는 메소드들은 아래와 같습니다.

S.N.	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 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.

HTTP Header Response 예제

아래 소스는 디지털 시계를 보여주기 위해서 Refresh헤더에 5초마다 새로고침하도록 setIntHeader() 메소드를 이용해서 값을 세팅하는 것을 보여주고 있습니다.

<%@ page import="java.io.*,java.util.*" %>
<html>
<head>
<title>Auto Refresh Header Example</title>
</head>
<body>
<center>
<h2>Auto Refresh Header Example</h2>
<%
   // Set refresh, autoload time as 5 seconds
   response.setIntHeader("Refresh", 5);
   // Get current time
   Calendar calendar = new GregorianCalendar();
   String am_pm;
   int hour = calendar.get(Calendar.HOUR);
   int minute = calendar.get(Calendar.MINUTE);
   int second = calendar.get(Calendar.SECOND);
   if(calendar.get(Calendar.AM_PM) == 0)
      am_pm = "AM";
   else
      am_pm = "PM";
   String CT = hour+":"+ minute +":"+ second +" "+ am_pm;
   out.println("Current Time is: " + CT + "\n");
%>
</center>
</body>
</html>

main.jsp 에 위 소스를 넣고 웹브라우저에서 요청하면 아래처럼 5초마다 새로고침되는 디지털 시계를 보실 수 있으실거에요.

Auto Refresh Header Example

Current Time is: 9:44:50 PM

Reference : http://www.tutorialspoint.com/jsp/jsp_server_response.htm

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💻 Programming/웹프로그래밍

AJAX란? - 서버로부터 응답받기

서버 응답

서버로부터 응답을 받기 위해서는 XMLHttpRequest객체의 responseText 또는 responseXML 속성을 사용합니다.

속성	설명
responseText	응답 데이터를 string으로 받습니다.
responseXML	응답 데이터를 XML 로 받습니다.

responseText 속성

예제

document.getElementById("demo").innerHTML = xhttp.responseText;

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responseXML 속성

예제

cd_catalog.xml 파일을 요청하고 응답으로 온 데이터 파싱하기

xmlDoc = xhttp.responseXML;
txt = "";
x = xmlDoc.getElementsByTagName("ARTIST");
for (i = 0; i < x.length; i++) {
  txt += x[i].childNodes[0].nodeValue + "<br>";
  }
document.getElementById("demo").innerHTML = txt;

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응답을 받는거는 했는데 그렇다면 응답이 왔는지는 어떻게 알 수 있나요?

자, 그 부분에 대해서는 다음 포스팅에 있을 이벤트에 대해서 공부를 하고나면 아실 수 있습니다.

자, 다음 시간에는 AJAX에서 사용되는 이벤트에 대해서 알아보도록 하겠습니다.