About session variables

Session variables store information (usually form or URL parameters submitted by users) and make it available to all of a web application’s pages for the duration of the user’s visit. For example, when users log on to a web portal that provides access to e‑mail, stock quotes, weather reports, and daily news, the web application stores the login information in a session variable that identifies the user throughout the site’s pages. This allows the user to see only the types of content they have selected as they navigate through the site. Session variables can also provide a safety mechanism by terminating the user’s session if the account remains inactive for a certain period of time. This also frees server memory and processing resources if the user forgets to log off a website.

Session variables store information for the life of the use session. The session begins when the user opens a page within the application and ends when the user does not open another page in the application for a certain period of time, or when the user explicitly terminates the session (typically by clicking a “log-off” link). While it exists, the session is specific to an individual user, and every user has a separate session.

Use session variables to store information that every page in a web application can access. The information can be as diverse as the user’s name, preferred font size, or a flag indicating whether the user has successfully logged in. Another common use of session variables is to keep a running tally, such as the number of questions answered correctly so far in an online quiz, or the products the user selected so far from an online catalog.

Session variables can only function if the user’s browser is configured to accept cookies. The server creates a session ID number that uniquely identifies the user when the session is first initiated, then sends a cookie containing the ID number to the user’s browser. When the user requests another page on the server, the server reads the cookie in the browser to identify the user and to retrieve the user’s session variables stored in the server’s memory.

Before creating a session variable, you must first obtain the information you want to store, and then send it to the server for storage. You can gather and send information to the server using HTML forms or hypertext links containing URL parameters. You can also obtain information from cookies stored on the user’s computer, from the HTTP headers sent by the user’s browser with a page request, or from a database.

A typical example of storing URL parameters in session variables is a product catalog that uses hard-coded URL parameters created using a link to send product information back to the server to be stored in a session variable. When a user clicks the “Add to shopping cart” link, the product ID is stored in a session variable while the user continues to shop. When the user proceeds to the check-out page, the product ID stored in the session variable is retrieved.

A form-based survey is a typical example of a page that stores form parameters in session variables. The form sends the selected information back to the server, where an application page scores the survey and stores the responses in a session variable to be passed to an application that might tally up the responses gathered from the survey population. Or the information might be stored in a database for later use.

After information is sent to the server, you store the information in session variables by adding the appropriate code for your server model to the page specified by the URL or form parameter. Referred to as the destination page, this page is specified in either the action attribute of the HTML form or the href attribute of the hypertext link on the starting page.

After you store a value in a session variable, you can use Dreamweaver to retrieve the value from session variables and use it in a web application. After you define the session variable in Dreamweaver, you can insert its value in a page.

The HTML syntax for each appears as follows:

<form action="destination.html" method="get" name="myform"> </form> 
<param name="href"value="destination.html">

Both the server technology used and the method you use to obtain the information determines the code used to store the information in a session variable. The basic syntax for each server technology is as follows:

<CFSET session.variable_name = value>

<% Session("variable_name") = value %>

<CFSET session.prodID = url.product>

<% Session("prodID") = Request.QueryString("product") %>

<CFSET session.prodID = form.txtProduct>

<% Session("prodID") = Request.Form("txtProduct") %>

You’re working on a site with a large audience of senior citizens. In Dreamweaver, add two links to the Welcome screen that let users customize the size of the site’s text. For larger, easy-to-read text, the user clicks one link, and for regular-size text, the user clicks another link.

Each link has a URL parameter called fontsize that submits the user’s text preference to the server, as the following Adobe ColdFusion® example shows:

<a href="resort.cfm?fontsize=large">Larger Text</a><br> 
<a href="resort.cfm?fontsize=small">Normal Text</a>

Store the user’s text preference in a session variable and use it to set the font size on each page the user requests.

Near the top of the destination page, enter the following code to create a session called font_pref that stores the user’s font size preference.

<CFSET session.font_pref = url.fontsize>

<% Session("font_pref") = Request.QueryString("fontsize") %>