|
Using Cookies
Part:
1
2
3
4
5
This chapter describes:
- What Is Cookie?
- Sending and Receiving Cookies
- Persistent Cookies
- Dumping HTTP Response with Cookies
What Is Cookie?
Cookie: A small amount of information sent by a Web server to
a Web browser, saved by the browser, and sent back to the server later.
Cookies are transmitted inside the HTTP header.
Cookies move from server to browser, and back to server as follows:
Web Web Local Web Web
Server Browser System Browser Server
Send Receive Save Send back Receive
cookies --> cookies --> cookies --> cookies --> cookies
As you can see from the diagram, cookies are actually saved to the hard disk
of Web browser user's machines. Many users are concerned about this. But I think
it is pretty safe to allow your browser to save cookies.
If you are really concerned, you can change your browser's settings to reject
cookies. But this may cause many Web based applications fail to run on your
browser.
Sending and Receiving Cookies
Sending cookies to the browser can be done by the addCookie() method on
the response object; while receiving cookies from the browser can be done
by the getCookies() method on the request object. Here is program to
demonstrate how to use those methods:
<?xml version="1.0"?>
<jsp:root xmlns:jsp="http://java.sun.com/JSP/Page" version="1.2">
<!--
- CookieTest.jsp
- Copyright (c) 2002 by Dr. Herong Yang, http://www.herongyang.com/
-->
<jsp:directive.page contentType="text/html"/>
<html><body>
<p>
<jsp:directive.page import="javax.servlet.http.Cookie"/>
<jsp:scriptlet><![CDATA[
out.println("<b>Cookies received by the server:</b><br/>");
Cookie[] cookies = request.getCookies();
int n = 0;
if (cookies!=null) {
n = cookies.length;
for (int i=0; i<cookies.length; i++) {
out.println(cookies[i].getName()+": "
+cookies[i].getValue()+"<br/>");
}
}
out.println("<b>Cookies added by the server:</b><br/>");
Cookie c = new Cookie("Cookie_"+n,"value");
out.println(c.getName()+": "+c.getValue()+"<br/>");
response.addCookie(c);
]]></jsp:scriptlet>
</p>
</body></html>
</jsp:root>
(Continued on next part...)
Part:
1
2
3
4
5
| 