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ASP Web Programming Course
Lesson 5
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5-1 Introduction
Before we start this lesson let's see how does web or http
protocol work. When you type an address in your bar and press
"enter" key, browser creates a socket connection to the
server and asks for a html file ( a web page in fact) server
sends the file and closes the connection.
Browser parses the html code and connects to server and asks
for each picture file needed for the page. Each picture file
(gif or jpg normally) is received in a separate connection.
As you see there will be no way for the server to know
someone from one connection to next one.
5-2 What is a session?
In complex applications we will want to recognize each user
from the other when more than one user uses a specific
application. For example we may want to remember the name of
each person who is connected to server until he decides to
leave. Something called a session will be used for this
purpose.
A session starts when a user requests a page from the server
for the first time and ends after user leaves.
In fact a session ends after a specific time since user's
last request to web server. Default time for session time out
is 20 minutes.
Session are used to store some information about the user on
server.
Each user connected to a website will have a separate session
and a unique session number.
For example support we want to chose some books from
different pages of a bookshop website. We can use session
variables (variables stored in a session) to hold choices. At
the end we can calculate the invoice using the information
saved in session.
As another examples you have seen modern websites that will
remember you on a different pages on their site after you log
in for the first time.
Your information such as your name is saved on your session.
This information will be retrieved by next pages and your
name is displayed on other pages with this method.
5-3 Storing info in sessions
Storing a variable in a session is very easy. We will use
session objects to do this.
session("name")="John"
Executing above code for the first time will create a session variable and will assign tha value "John" to it.
Now regardless of the ASP page being executed on the server,
we have access to session variable. We can retrieve stored
with below code.
user=session("name")
Now let's see an example. You may remember example 4-1 of
previous lesson.
We have modified login example of previous lesson for our
next example.
Example 5-1:
login.html:
<html>
<head>
<title>Login Page</title>
</head>
<body>
<form action="login.asp" method="post">
User Name: <input type="text" name="username"><br>
Password: <input type="password" name="pass"><br>
<input type="submit" value="Enter">
</form>
</body>
</html>
login.asp:
<%
username=Request.Form("username")
pass=Request.Form("pass")
session("user")=username
%>
<html>
<head>
<title>Welcome Page</title>
</head>
<body>
Dear <%=username%>, Welcome to Board<br>
Your password is <%=pass%>
<br>
<a href="clubs.asp">Click here to go to clubs</a>
</body>
</html>
clubs.asp:
<%
username=session("user")
%>
<html>
<head>
<title>Clubs Page</title>
</head>
<body>
Dear <%=username%>, Welcome to Clubs Again<br>
</body>
</html>
We have not modified login.html file but we have added below line to login.asp page.
session("user")=username
This will create a session variable "user" and store username in this variable.
We have also added a link to another asp page. We have
assumed this page to be start page of our clubs section.
In this page we have used below code to retrieve username
that we stored in login.asp page.
username=session("user")
Now that we have retrieved user name we can display it on
other pagesusing below code.
Dear <%=username%>, welcome to clubs.
5-4 Session time out
As we told latter, default time out for a session is 20
minutes. This means that if a user does not request a new page in 20 minutes, all session information will be lost.
If you develop applications that you expect long idle times,
you will need to modify default time out. For example you may
want to write programs that need large amounts of information
to be filled in forms before submitting and this may loose
session information.
Modifying session information is very easy.
<%session.timeout=45%>
Above code will change time out to 45 minutes.
5-4 Terminating a session
As we saw latter you can save information about users in
session variables. Sometimes you may want to end a session
and remove more information using your code.
An example is a "logout" link on your application.
If you are using session information for logged in users, you
may logout them by terminating their session and therefore
removing their information from session variables.
Then you must test to see if user has valid session
variables (ie username etc.) before doing something.
As an example a webmail system will not let a user to see
mails or do anything if his session has timeout or terminated
by clicking on logout link.
You can terminate a session by below code.
<%session.abandon%>
5-6 End of this lesson
This lesson ends here. Until now we have learned some general ASP programming concepts. But there are more. ASP control structures, Applications, Cookies, Database, Mail
,... are among the subjects we will study in ASP web programming course.
We will stop here and you will have enough time to work on
your own applications.
Notice: You can find examples of this lessons in our website. There you must go to resources section and then click on
"ASP
email course example page."
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Attention: Do not use any html editing program like MS FrontPage . You must work on the codes yourself. Package files related to each exercise into a single zip file and send this file to your tutor. |
| Course support: Paid students must send exercises to their tutor. Tutor will return corrected exercise to the student. Others can ask their questions in Support forums in our web site. Free students can also submit their homework in related support forum for correction and advice from tutor. |
1- Write a small counter code that you can add it to your
ASP pages, so that it can count each view of the page. Use a
session variable this time. Why this type of counter cannot
be used effectively?
Course Project 1:
Design a login page with three fields. First and second
fields are user name and password. Third field will contain 5
radio buttons (in fact we will have 7 controls on our form).
User must be able to choose an Icon (a small bitmap that will
stand next to each radio button) as his sign.
After pressing the login button user will go to another page.
(by clicking on alink)
In this new page you must display both user name and the icon
chosen by user.
============================================================
Copyright Notice :
© 2000,2001 Siamak Sarmady and Learnem
Group . All rights reserved. This text is licensed to be used on
ProgrammingUni website. Any kind of reproduction, redistribution in any form is
strictly prohibited without written permission of the writer.
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