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Throwing JavaScript Into the (Cookie Dough) Mix - 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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Since our cookies are stored on our client, our client Internet browser can access them using JavaScript.  We do just that in the file grabcookievaluewithjavascript.html whose code is shown in Listing 3 below. 


<HTML>
<HEAD>
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<META name="GENERATOR" content="IBM WebSphere Studio">
<META http-equiv="Content-Style-Type" content="text/css">
<LINK href="theme/Master.css" rel="stylesheet" type="text/css">
<TITLE>JavaScript Cookie Demo</TITLE>
<SCRIPT language="JavaScript">
<!--
 
function GetCookieValue(offset)
 
{
  
var endstr document.cookie.indexOf (";"offset);
  
if (endstr == -1)
      endstr 
document.cookie.length;
  document
.write(document.cookie.substring(offsetendstr));
  
return unescape(document.cookie.substring(offsetendstr));
 
}
 

 
function ReportCookieValue (cookieName
 
{
  
var arg cookieName "=";
    
var alen arg.length;
  
var clen document.cookie.length;
  
var 0;
    
while (clen
    
{
     

      
var alen;
      
var sub document.cookie.substring(i,j);
      
if (sub == arg)
      
{
         
return GetCookieValue(j);
        
}
      
else document.cookie.indexOf(" "i) + 1;
      
if (== 0) break; 
      

    
}    
    
return null;
 
}
// -->
</SCRIPT>
</HEAD>
<BODY>
<p></p>
<h2>According to JavaScript, you like <script language="JavaScript">
 
<!--//ReportCookieValue("FavoriteCookieType")//-->
 
</script> Cookies .</h2>
<p></p>
 
</BODY>
</HTML>

Listing 3: grabcookiewithjavascript.html

The output of our JavaScript cookie extraction is shown below:

Client State with Cookies in Java

 
Figure 6: Extracting our Cookie Value on the Client via JavaScript 

Being able to access your cookies via JavaScript represents a powerful functionality. By doing this, you can have forms preloaded with what is resident in client cookie data. As an exercise, you should try and modify favoritecookie.html to initially present the pull down value that was resident in your cookie.



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

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