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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
<h1>ASP Session Object</h1>
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<p class="intro">The Session object is used to store information about, or change settings for
a user session. Variables stored in the Session object hold information about one single
user, and are available to all pages in one application. </p>
<hr />
<h2>The Session object </h2>
<p>When you are working with an application, you open it, do some changes and then
you close it. This is much like a Session. The computer knows who you are. It
knows when you start the application and when you end. But on the internet there is one
problem: the web server does not know who you are and what you do because the HTTP address doesn't maintain
state. </p>
<p>ASP solves this problem by creating a unique cookie for each user. The cookie
is sent to the client and it contains information that identifies the user. This
interface is called the Session object. </p>
<p>The Session object is used to store information about, or change settings for
a user session. Variables stored in the Session object hold information about one single
user, and are available to all pages in one application. Common information
stored in session variables are name, id, and preferences. The server creates a
new Session object for each new user, and destroys the Session object when the session expires. </p>
<hr />
<h2>When does a Session Start?</h2>
<p>A session starts when: </p>
<ul>
<li>A new user requests an ASP file, and the Global.asa
file includes a Session_OnStart procedure</li>
<li>A value is stored in a Session variable</li>
<li>A user requests an ASP file, and the Global.asa file uses the <object> tag to instantiate an object with session
scope</li>
</ul>
<hr />
<h2>When does a Session End?</h2>
<p>A session ends if a user has not requested or refreshed a page in the application for a specified period.
By default, this is 20 minutes. </p>
<p>If you want to set a timeout interval that is shorter or longer than the default, you can
set the <b>Timeout</b> property.</p>
<p>The example below sets a timeout interval of 5 minutes:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
Session.Timeout=5
%></pre>
</td>
</tr>
</table>
<p>To end a session immediately, you may use the <b>Abandon</b> method:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td>
<pre><%
Session.Abandon
%></pre>
</td>
</tr>
</table>
<p><b>Note:</b> The main problem with sessions is WHEN they should end. We do
not know if the user's last request was the final one or not. So we do not know
how long we should keep the session "alive". Waiting too long for an idle
session uses up resources on the server, but if the session is deleted too soon
the user has to start all over again because the server has deleted all the
information. Finding the right timeout interval can be difficult!</p>
<p><b>Tip:</b> If you are using session variables, store SMALL amounts of data
in them. </p>
<hr />
<h2>Store and Retrieve Session Variables </h2>
<p>The most important thing about the Session object is that you can store variables in it.</p>
<p>The example below
will set the Session variable <i>username</i> to "Donald Duck" and the Session variable <i>age</i>
to "50":</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
Session("username")="Donald Duck"
Session("age")=50
%></pre>
</td>
</tr>
</table>
<p>When the value is stored in a session variable it can be reached from ANY page
in the ASP application:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre>Welcome <%Response.Write(Session("username"))%></pre>
</td>
</tr>
</table>
<p>The line above returns: "Welcome Donald Duck".</p>
<p>You can also store user preferences in the Session object, and then access
that preference to choose what page to return to the user. </p>
<p>The example below specifies a text-only version of the page if the user has a
low screen resolution: </p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%If Session("screenres")="low" Then%>
This is the text version of the page
<%Else%>
This is the multimedia version of the page
<%End If%></pre>
</td>
</tr>
</table>
<br />
<hr />
<h2>Remove Session Variables </h2>
<p>The Contents collection contains all session variables.</p>
<p>It is possible to remove a session variable with the Remove method.</p>
<p>The example below removes the session variable "sale" if the value of the
session variable "age" is lower than 18: </p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
If Session.Contents("age")<18 then
Session.Contents.Remove("sale")
End If
%></pre>
</td>
</tr>
</table>
<p>To remove all variables in a session, use the RemoveAll method: </p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
Session.Contents.RemoveAll()
%></pre>
</td>
</tr>
</table>
<br />
<hr />
<h2>Loop Through the Contents Collection</h2>
<p>The Contents collection contains all session variables. You can loop through
the Contents collection, to see what's stored in it: </p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
Session("username")="Donald Duck"
Session("age")=50</pre>
<pre>dim i
For Each i in Session.Contents
Response.Write(i & "<br />")
Next
%></pre>
</td>
</tr>
</table>
<p>Result:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td>
<pre>username
age</pre>
</td>
</tr>
</table>
<p>If you do not know the number of items in the Contents collection,
you can use the Count property:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td>
<pre><%
dim i
dim j
j=Session.Contents.Count
Response.Write("Session variables: " & j)
For i=1 to j
Response.Write(Session.Contents(i) & "<br />")
Next
%></pre>
</td>
</tr>
</table>
<p>Result:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr><td>
<pre>Session variables: 2
Donald Duck
50</pre>
</td>
</tr>
</table>
<br />
<hr />
<h2>Loop Through the StaticObjects Collection</h2>
<p>You can loop through the StaticObjects collection, to see the
values of all objects stored in the Session object:</p>
<table class="ex" cellspacing="0" border="1" width="100%">
<tr>
<td>
<pre><%
dim i
For Each i in Session.StaticObjects
Response.Write(i & "<br />")
Next
%></pre>
</td>
</tr>
</table>
<br />
<hr />
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<p>From <b>http://www.w3schools.com</b> (Copyright Refsnes Data)</p>
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