When you are working with an application on your computer, 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 open the application and when you close it. However, 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.
ASP solves this problem by creating a unique cookie for each user. The cookie is sent to the user's computer and it contains information that identifies the user. This interface is called the Session object.
The Session object stores information about, or change settings for a user session.
Variables stored in a 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.
When does a Session Start?
A session starts when:
• A new user requests an ASP file, and the Global.asa file includes a Session_OnStart procedure
• A value is stored in a Session variable
• A user requests an ASP file, and the Global.asa file uses the tag to instantiate an object with session scope
When does a Session End? 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. If you want to set a timeout interval that is shorter or longer than the default, use the Timeout property. The example below sets a timeout interval of 5 minutes: <% Session.Timeout=5 %> Use the Abandon method to end a session immediately: <% Session.Abandon %> Note: 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! Tip: Only store SMALL amounts of data in session variables!
Store and Retrieve Session Variables The most important thing about the Session object is that you can store variables in it. The example below will set the Session variable username to "Donald Duck" and the Session variable age to "50": <% Session("username")="Donald Duck" Session("age")=50 %> When the value is stored in a session variable it can be reached from ANY page in the ASP application: Welcome <%Response.Write(Session("username"))%> The line above returns: "Welcome Donald Duck". You can also store user preferences in the Session object, and then access that preference to choose what page to return to the user. The example below specifies a text-only version of the page if the user has a low screen resolution: <%If Session("screenres")="low" Then%> This is the text version of the page <%Else%> This is the multimedia version of the page <%End If%>
Remove Session Variables The Contents collection contains all session variables. It is possible to remove a session variable with the Remove method. The example below removes the session variable "sale" if the value of the session variable "age" is lower than 18: <% If Session.Contents("age")<18 then Session.Contents.Remove("sale") End If %> To remove all variables in a session, use the RemoveAll method: <% Session.Contents.RemoveAll() %>
Loop Through the Contents Collection The Contents collection contains all session variables. You can loop through the Contents collection, to see what's stored in it: <% Session("username")="Donald Duck" Session("age")=50 dim i For Each i in Session.Contents Response.Write(i & " ") Next %> Result: username age If you do not know the number of items in the Contents collection, you can use the Count property: <% dim i dim j j=Session.Contents.Count Response.Write("Session variables: " & j) For i=1 to j Response.Write(Session.Contents(i) & " ") Next %> Result: Session variables: 2 Donald Duck 50
Loop Through the StaticObjects Collection You can loop through the StaticObjects collection, to see the values of all objects stored in the Session object: <% dim i For Each i in Session.StaticObjects Response.Write(i & " ") Next %> 9. ASP Application Object A group of ASP files that work together to perform some purpose is called an application.
Application Object An application on the Web may consists of several ASP files that work together to perform some purpose. The Application object is used to tie these files together. The Application object is used to store and access variables from any page, just like the Session object. The difference is that ALL users share ONE Application object (with Sessions there is ONE Session object for EACH user). The Application object holds information that will be used by many pages in the application (like database connection information). The information can be accessed from any page. The information can also be changed in one place, and the changes will automatically be reflected on all pages.
Store and Retrieve Application Variables Application variables can be accessed and changed by any page in an application. You can create Application variables in "Global.asa" like this: In the example above we have created two Application variables: "vartime" and "users". You can access the value of an Application variable like this: There are <% Response.Write(Application("users")) %> active connections.
Loop Through the Contents Collection The Contents collection contains all application variables. You can loop through the Contents collection, to see what's stored in it: <% dim i For Each i in Application.Contents Response.Write(i & " ") Next %> If you do not know the number of items in the Contents collection, you can use the Count property: <% dim i dim j j=Application.Contents.Count For i=1 to j Response.Write(Application.Contents(i) & " ") Next %> Loop Through the StaticObjects Collection You can loop through the StaticObjects collection, to see the values of all objects stored in the Application object: <% dim i For Each i in Application.StaticObjects Response.Write(i & " ") Next %>
Lock and Unlock You can lock an application with the "Lock" method. When an application is locked, the users cannot change the Application variables (other than the one currently accessing it). You can unlock an application with the "Unlock" method. This method removes the lock from the Application variable: <% Application.Lock 'do some application object operations Application.Unlock %> 10.ASP Including Files The #include Directive You can insert the content of one ASP file into another ASP file before the server executes it, with the #include directive. The #include directive is used to create functions, headers, footers, or elements that will be reused on multiple pages.
