18/12/2016
BCA 6th Sem.
BCS-053 some solved questions.
Q. What are cookies ? Write a program to create cookies to store User ID and password of the client on his/her machine.
[12:27 PM, 12/18/2016] +91 88604 68870: Ans. : Cookies : Cookies are text files stored on the client computer and they are kept for various information tracking purpose. Java Servlets transparently supports HTTP cookies. There are three steps involved in identifying returning users: Server script sends a set of cookies to the browser
Cookies are text files stored on the client computer and they are kept for various information tracking purpose. Java Servlets transparently supports HTTP cookies.
There are three steps involved in identifying returning users:
Server script sends a set of cookies to the browser. For example name, age, or identification number etc.
Browser stores this information on local machine for future use.
When next time browser sends any request to web server then it sends those cookies information to the server and server uses that information to identify the user.
This chapter will teach you how to set or reset cookies, how to access them and how to delete them.
The Anatomy of a Cookie:
Cookies are usually set in an HTTP header (although JavaScript can also set a cookie directly on a browser). A servlet that sets a cookie might send headers that look something like this:
HTTP/1.1 200 OK
Date: Fri, 04 Feb 2000 21:03:38 GMT
Server: Apache/1.3.9 (UNIX) PHP/4.0b3
Set-Cookie: name=xyz; expires=Friday, 04-Feb-07 22:03:38 GMT;
path=/; domain=tutorialspoint.com
Connection: close
Content-Type: text/html
As you can see, the Set-Cookie header contains a name value pair, a GMT date, a path and a domain. The name and value will be URL encoded. The expires field is an instruction to the browser to "forget" the cookie after the given time and date.
If the browser is configured to store cookies, it will then keep this information until the expiry date. If the user points the browser at any page that matches the path and domain of the cookie, it will resend the cookie to the server. The browser's headers might look something like this:
GET / HTTP/1.0
Connection: Keep-Alive
User-Agent: Mozilla/4.6 (X11; I; Linux 2.2.6-15apmac ppc)
Host: zink.demon.co.uk:1126
Accept: image/gif, /
Accept-Encoding: gzip
Accept-Language: en
Accept-Charset: iso-8859-1,*,utf-8
Cookie: name=xyz
A servlet will then have access to the cookie through the request method request.getCookies() which returns an array of Cookie objects.
Servlet Cookies Methods:
Following is the list of useful methods which you can use while manipulating cookies in servlet.
S.N. Method & Description
1
public void setDomain(String pattern)
This method sets the domain to which cookie applies, for example tutorialspoint.com.
2
public String getDomain()
This method gets the domain to which cookie applies, for example tutorialspoint.com.
3
public void setMaxAge(int expiry)
This method sets how much time (in seconds) should elapse before the cookie expires. If you don't set this, the cookie will last only for the current session.
4
public int getMaxAge()
This method returns the maximum age of the cookie, specified in seconds, By default, -1 indicating the cookie will persist until browser shutdown.
5
public String getName()
This method returns the name of the cookie. The name cannot be changed after creation.
6
public void setValue(String newValue)
This method sets the value associated with the cookie.
7
public String getValue()
This method gets the value associated with the cookie.
8
public void setPath(String uri)
This method sets the path to which this cookie applies. If you don't specify a path, the cookie is returned for all URLs in the same directory as the current page as well as all subdirectories.
9
public String getPath()
This method gets the path to which this cookie applies.
10
public void setSecure(boolean flag)
This method sets the boolean value indicating whether the cookie should only be sent over encrypted (i.e. SSL) connections.
11
public void setComment(String purpose)
This method specifies a comment that describes a cookie's purpose. The comment is useful if the browser presents the cookie to the user.
12
public String getComment()
This method returns the comment describing the purpose of this cookie, or null if the cookie has no comment.
[12:27 PM, 12/18/2016] +91 88604 68870: Ex. Example:
Let us modify our Form Example to set the cookies for first and last name.
// Import required java libraries
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
// Extend HttpServlet class
public class HelloForm extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
// Create cookies for first and last names.
Cookie firstName = new Cookie("first_name",
request.getParameter("first_name"));
Cookie lastName = new Cookie("last_name",
request.getParameter("last_name"));
// Set expiry date after 24 Hrs for both the cookies.
firstName.setMaxAge(60*60*24);
lastName.setMaxAge(60*60*24);
// Add both the cookies in the response header.
response.addCookie( firstName );
response.addCookie( lastName );
// Set response content type
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String title = "Setting Cookies Example";
String docType =
"\n";
out.println(docType +
"\n" +
"" + title + "\n" +
"\n" +
"" + title + "\n" +
"\n" +
" First Name: "
+ request.getParameter("first_name") + "\n" +
" Last Name: "
+ request.getParameter("last_name") + "\n" +
"\n" +
"");
}
}
