What is ASP ?

An ASP file can contain text, HTML tags and scripts.
Scripts in an ASP file are executed on the server.

  • ASP stands for Active Server Pages
  • ASP is a program that runs inside IIS
  • IIS stands for Internet Information Services
  • IIS is as a free component with Windows 2000
  • IIS is also a part of the Windows NT 4.0
  • PWS is a smaller but fully functional version of IIS
  • PWS can be found on your Windows 95/98 CD

 

 

 

 

 

 

     

     

 

 

 

ASP Compatibility

  • ASP is a Microsoft Technology
  • To run IIS you must have Windows NT 4.0 or later
  • To run PWS you must have Windows 95 or later
  • ChiliASP is a technology that runs ASP without Windows OS
  • InstantASP is another technology that runs ASP without Windows

What is an ASP File?

  • An ASP file is just the same as an HTML file
  • An ASP file can contain text, HTML, XML, and scripts
  • Scripts in an ASP file are executed on the server
  • An ASP file has the file extension ".asp"

How Does ASP Differ from HTML?

  • When a browser requests an HTML file, the server returns the file
  • When a browser requests an ASP file, IIS passes the request to the ASP engine. The ASP engine reads the ASP file, line by line, and executes the scripts in the file. Finally, the ASP file is returned to the browser as plain HTML
  • You cannot view the ASP source code by selecting "View source" in a browser, you will only see the output from the ASP file, which is plain HTML. This is because the scripts are executed on the server before the result is sent back to the browser.

What can ASP do for you?

  • Dynamically edit, change or add any content of a Web page
  • Respond to user queries or data submitted from HTML forms
  • Access any data or databases and return the results to a browser
  • Customize a Web page to make it more useful for individual users
  • The advantages of using ASP instead of CGI and Perl, are those of simplicity and speed
  • Provides security since your ASP code can not be viewed from the browser
  • Since ASP files are returned as plain HTML, they can be viewed in any browser
  • Clever ASP programming can minimize the network traffic

The Basic Syntax Rule 

An ASP file normally contains HTML tags, just like an HTML file. However, an ASP file can also contain server scripts, surrounded by the delimiters <% and %>. Server scripts are executed on the server, and can contain any expressions, statements, procedures, or operators valid for the scripting language you prefer to use. 

The Response Object 

The Write method of the ASP Response Object is used to send content to the browser. For example, the following statement sends the text "Hello World" to the browser:
  
<%
response.write("Hello World!")
%>

VBScript

You may use different scripting languages in ASP files. However, the default scripting language is VBScript:
  
<html>
<body>
<%
response.write("Hello World!")
%>
</body>
</html>

The example above writes "Hello World!" into the body of the document. 

JavaScript 

To set JavaScript as the default scripting language for a particular page you must insert a language specification at the top of the page:
  
<%@ language="javascript"%>
<html>
<body>
<%
Response.Write("Hello World!")
%>
</body>
</html>

Note: Unlike VBScript - JavaScript is case sensitive. You will have to write your ASP code with uppercase letters and lowercase letters when the language requires it. 

Other Scripting Languages 

ASP is shipped with VBScript and JScript (Microsoft's implementation of JavaScript). If you want to script in another language, like PERL, REXX, or Python, you will have to install script engines for them.

Important: Because the scripts are executed on the server, the browser that displays the ASP file does not need to support scripting at all!

Procedures 

The ASP source code can contain procedures and functions: 
  
<html>
<head>
<%
sub vbproc(num1,num2)
response.write(num1*num2)
end sub
%>
</head>
<body>
<p>Result: <%call vbproc(3,4)%></p>
</body>
</html>

Insert the <%@ language="language" %> line above the <html> tag to write procedures or functions in another scripting language than default: 
  
<%@ language="javascript" %>
<html>
<head>
<%
function jsproc(num1,num2)
{
Response.Write(num1*num2)
}
%>
</head>
<body>
<p>Result: <%jsproc(3,4)%></p>
</body>
</html>

Differences Between VBScript and JavaScript

When calling a VBScript or a JavaScript procedure from an ASP file written in VBScript, you can use the "call" keyword followed by the procedure name. If a procedure requires parameters, the parameter list must be enclosed in parentheses when using the "call" keyword. If you omit the "call" keyword, the parameter list must not be enclosed in parentheses. If the procedure has no parameters, the parentheses are optional. 

When calling a JavaScript or a VBScript procedure from an ASP file written in JavaScript, always use parentheses after the procedure name. 

User Input 

The Request object may be used to retrieve user information from forms:
  
<form method="get" action="simpleform.asp">
First Name: <input type="text" name="fname">
<br />
Last Name: <input type="text" name="lname">
<br /><br />
<input type="submit" value="Submit">
</form>

User input can be retrieved in two ways: With Request.QueryString or Request.Form. 

Request.QueryString

The Request.QueryString command is used to collect values in a form with method="get". Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and has limits on the amount of information to send.

If a user typed "Bill" and "Gates" in the form example above, the URL sent to the server would look like this:
  
http://www.w3schools.com/simpleform.asp?fname=Bill&lname=Gates

Assume that the ASP file "simpleform.asp" contains the following script:
  
<body>
Welcome
<%
response.write(request.querystring("fname"))
response.write(" " & request.querystring("lname"))
%>
</body>

The browser will display the following in the body of the document:
  
Welcome Bill Gates

Request.Form 

The Request.Form command is used to collect values in a form with method="post". Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

If a user typed "Bill" and "Gates" in the form example above, the URL sent to the server would look like this: 
  
http://www.w3schools.com/simpleform.asp

Assume that the ASP file "simpleform.asp" contains the following script:
  
<body>
Welcome
<%
response.write(request.form("fname"))
response.write(" " & request.form("lname"))
%>
</body>

The browser will display the following in the body of the document:
  
Welcome Bill Gates

Form Validation

User input should be validated on the browser whenever possible (by client scripts). Browser validation is faster and you reduce the server load.

You should consider using server validation if the user input will be inserted into a database. A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.

What is a Cookie? 

A cookie is often used to identify a user. A cookie is a small file that the server embeds on the user's computer. Each time the same computer requests for a page with a browser, it will send the cookie too. With ASP, you can both create and retrieve cookie values.

How to Create a Cookie

The "Response.Cookies" command is used to create cookies.

Note: The Response.Cookies command must appear BEFORE the <html> tag.

In the example below, we will create a cookie named "firstname" and assign the value "Kirk" to it:
  
<%
Response.Cookies("firstname")="Kirk"
%>

It is also possible to assign properties to a cookie, like setting a date when the cookie should expire:
  
<%
Response.Cookies("firstname")="Kirk" 
Response.Cookies("firstname").Expires=#July 14,2003#
%>

How to Retrieve a Cookie Value

The "Request.Cookies" command is used to retrieve a cookie value.

In the example below, we retrieve the value of the cookie named "firstname" and display it on a page:
  
<%
fname=Request.Cookies("firstname")
response.write("Firstname=" & fname)
%>

Output:

Firstname=Alex

A Cookie with Keys

If a  cookie contains a collection of multiple values, we say that the cookie has Keys.

In the example below, we will create a cookie collection named "user". The "user" cookie has Keys that contains information about a user:
  
<%
Response.Cookies("user")("firstname")="Kirk"
Response.Cookies("user")("lastname")="Arnett"
Response.Cookies("user")("country")="USA"
%>
 

<html>
<body>
<%
dim x,y
for each x in Request.Cookies
  response.write("<p>")
  if Request.Cookies(x).HasKeys then
    for each y in Request.Cookies(x)
      response.write(x & ":" & y & "=" & Request.Cookies(x)(y))
      response.write("<br />")
    next
  else
    Response.Write(x & "=" & Request.Cookies(x) & "<br />")
  end if
  response.write "</p>"
next
%>
</body>
</html>

The Session object 

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. 

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 alled the Session object. 

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. 

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 <object> 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, you can set the Timeout property.

The example below sets a timeout interval of 5 minutes:
  
<%
Session.Timeout=5
%>

To end a session immediately, you may use the Abandon method:
  
<%
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 uses up resources on the server. But if the session is deleted too fast you risk that the user is coming back and the server has deleted all the information, so the user has to start all over again. Finding the right timeout interval can be difficult. 

Tip: If you are using session variables, store SMALL amounts of data in them. 

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 & "<br />")
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) & "<br />")
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 & "<br />")
Next
%>

Application Object

An application on the Web may be a group of ASP files. The ASP files work together to perform some purpose. The Application object in ASP 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, while with Sessions there is one Session object for EACH user.

The Application object should hold information that will be used by many pages in the application (like database connection information). This means that you can access the information from any page. It also means that you can change the information 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 the application.

You can create Application variables in "Global.asa" like this:
  
<script language="vbscript" runat="server">

Sub Application_OnStart
application("vartime")=""
application("users")=1
End Sub

</script>

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 & "<br />")
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) & "<br />")
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 & "<br />")
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
%>

 

 

Email: Dr. Kirk P. Arnett, CCP, DBA