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Chapter 8 Handling Cookies

Identifying a User During an E commerce 

Session

Many on line stores use a  shopping cart  metaphor in which the user selects

an item, adds it to his shopping cart, then continues shopping. Since the

HTTP connection is usually closed after each page is sent, when the user

selects a new item to add to the cart, how does the store know that it is the

same user that put the previous item in the cart? Persistent (keep alive)

HTTP connections (see Section 7.4) do not solve this problem, since persis 

tent connections generally apply only to requests made very close together in

time, as when a browser asks for the images associated with a Web page.

Besides, many servers and browsers lack support for persistent connections.

Cookies, however, can solve this problem. In fact, this capability is so useful

that servlets have an API specifically for session tracking, and servlet authors

don't need to manipulate cookies directly to take advantage of it. Session

tracking is discussed in Chapter 9.

Avoiding Username and Password

Many large sites require you to register in order to use their services, but it is

inconvenient to remember and enter the username and password each time

you visit. Cookies are a good alternative for low security sites. When a user

registers, a cookie containing a unique user ID is sent to him. When the cli 

ent reconnects at a later date, the user ID is returned, the server looks it up,

determines it belongs to a registered user, and permits access without an

explicit username and password. The site may also remember the user's

address, credit card number, and so forth, thus simplifying later transactions.

Customizing a Site

Many  portal  sites let you customize the look of the main page. They might

let you pick which weather report you want to see, what stock and sports

results you care about, how search results should be displayed, and so forth.

Since it would be inconvenient for you to have to set up your page each time

you visit their site, they use cookies to remember what you wanted. For sim 

ple settings, this customization could be accomplished by storing the page

settings directly in the cookies. Section 8.6 gives an example of this. For more

complex customization, however, the site just sends the client a unique iden 

tifier and keeps a server side database that associates identifiers with page

settings. 

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

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