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Setting Cookies on 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. I’ll 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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CookieSetterServlet is one of the servlets you will find in the EAR.  You can find the code for this servlet in Listing 1. 


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 1: CookieSetterServlet.java

The servlet grabs a parameter from the request named FavoriteCookiePreference.    Note that the HTML file, favoritecookie.html calls the servlet and feeds the servlet with request data (see Figure 3).

Client State with Cookies in Java

 
Figure 3: favoritecookie.html Feeds
CookieSetterServletwith Request Data

Our code to create a cookie on the server side and send it back to the client is a straightforward process.  We simply create a new Cookie object by calling the constructor with the name of the cookie we want to create and its associated value (the value we collected from our request). 

In the code, we also set a comment for the cookie.  Finally, the resulting Cookie object is packaged to be shipped back to the client by calling the Response object’s addCookie method, which takes our new Cookie as an argument.

For some visual feedback, the servlet reports to the user what was extracted from the request (see Figure 4).


Client State with Cookies in Java

Figure 4: Output of the CookieSetterServlet
Servlet, After Sending the Cookie to the Client

It is important to note that we added the cookie to our Response object before using our PrintWriter object. This order is mandatory if you want things to work. Your cookie is going to be sent back to the client as a header; headers must be written before accessing the PrintWriter.

It is also important to note that the cookies that a server places on a client are associated only to that server. 

Coming up, we’ll use a different servlet to grab our cookie’s value from the client.  Note that since this second servlet will reside on the same server as our first servlet, we are able to access the client cookie we established (which we named FavoriteCookieType).



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

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