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Grabbing Cookies From Your Client - Java

Cookies serve as a facility for servers to send information to a client.†† This information is then housed on the client, from which the server can later retrieve the information.†In this article, we will study the concept of saving client state with cookies using Java Servlets.†Iíll walk you through an end to end example where you will store and retrieve data using cookies.

TABLE OF CONTENTS:
  1. Saving Client State with Cookies and Java
  2. Some Background Information About Cookies
  3. Setting Cookies on Your Client
  4. Grabbing Cookies From Your Client
  5. Throwing JavaScript Into the (Cookie Dough) Mix
  6. Cleaning Up: Getting Rid of Cookie Crumbs
By: Kulvir Singh Bhogal
Rating: starstarstarstarstar / 57
March 24, 2004

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Extracting cookies from your client is also a straightforward process, courtesy of the Java APIs provided to us.  The acquisition process of the cookie we set using the CookieSetterServlet is shown in Listing 2. 


import java.io.IOException;
import java
.io.PrintWriter;
import javax
.servlet.Servlet;
import javax
.servlet.ServletException;
import javax
.servlet.http.Cookie;
import javax
.servlet.http.HttpServlet;
import javax
 
.servlet
 
.http
 
.HttpServletRequest;
import javax
 
.servlet
 
.http
 
.HttpServletResponse;
 
public class 
CookieSetterServlet
 
extends HttpServlet
 
implements Servlet
{
 
public void doGet(
  HttpServletRequest request
,
  HttpServletResponse response
)
  throws ServletException
IOException
 
{
  
// grab the user's favorite cookie type from the request
  String favoriteCookieType =
   request.getParameter(
    "FavoriteCookiePreference");
  // report the value to the console
  System.out.println(
   "Setting favorite cookie type to: "
    + favoriteCookieType);
  // create a new Cookie object.  
  // set the token name to "FavoriteCookieType"
  // set the value to the value extracted from the request
  Cookie favoriteCookie =
   new Cookie(
    "FavoriteCookieType",
    favoriteCookieType);
  // set the value of the comment
  favoriteCookie.setComment(
   "Houses User's Favorite Cookie Type");
  // add the cookie to the response
  response.addCookie(
   favoriteCookie);
  // provide some visual feedback to the user
  PrintWriter out =
   response.getWriter();
  out.println(
   " "
    + "");
  out.println(
   " 
<H2>I am now going to "remember" that you like "
    + favoriteCookieType
    + " 
cookiesusing Cookies.</H2>");
  out.println("");
 }
 public void doPost(
  HttpServletRequest request,
  HttpServletResponse response)
  throws ServletException, IOException
 {
  doGet(request, response);
 }
}

Listing 2: CookieSetterServlet.java

To obtain the cookie from the client, we obtain our cookies as an array of Cookie objects from the Request object.   We then have to cycle through the array, looking for the name of the cookie of our interest.  Once we find the correct cookie, we extract its value and present the value to the user (see Figure 5).

Client State with Cookies in Java

Figure 5: Output of the CookieGrabberServlet, which
Reports the Value of the Cookie Seen on the Client 



 
 
>>> More Java & J2EE Articles          >>> More By Kulvir Singh Bhogal
 

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