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ASP ( Active Server Pages )

                 Index              

 

What Is ASP?

"Active Server Pages" abbreviated as ASP, is a server-side scripting environment developed by Microsoft. Using ASP, we can create and run dynamic and interactive web server applications. With ASP, we can combine HTML pages, script commands, and COM components to create interactive Web pages or powerful Web-based applications, which are easy to develop and modify.
             The default scripting language used for writing ASP is VBScript although we can use JavaScript. All ASP pages will be executed at the server and the page will have the extension ".asp".
             An ASP page cannot run by simply opening it in a web browser. The page must be requested through a web server that supports ASP, this is why ASP stands for Active Server Pages, no server, no active pages.
              When a browser requests an ASP page, the web server interprets any ASP contained within the web page before sending the HTML produced to the browser. In this way, the entire ASP is run on the web server and no ASP will ever be passed back to the web browser.
 

Installing ASP

Just as we have seen before, for running ASP we need a web server, which need not be an external. We can install web server in our PC. Microsoft provides web servers such as Personal Web Server (PWS) which can be run on any Windows95/98, NT or 2000 workstation and Internet Information Server (IIS) for Windows NT or Windows 2000 based web servers.
Installing Personal Web Server (PWS)
              Personal Web Server ships with Windows 98 CD, you can find it in add-ons folder present in the Windows 98 CD. If you are using Windows 95, you have to download "Windows NT 4.0 Option Pack" from Microsoft.
 

1. Insert your Windows 98 CD into your CD-ROM Drive.
2. Explore your CD-ROM Drive.
3. Open “add-ons” folder, there you will find “pws” folder, run “setup.exe” from this folder.
4. Follow the instructions on the screen to install “Personal Web Server”

After installation of PWS, you will find a PWS icon on your desktop and most probably a small icon of PWS in the right corner of the taskbar. Open any one of them. If the PWS is running then you will see an option "Stop PWS" or else you will see "Start PWS".
             To check if PWS is running, open your Internet Explorer. In the URL box enter http://127.0.0.1 or http://localhost and press Enter. If everything is working fine, you will see a default page generated by PWS. If you can see any page then PWS is running correctly or else you have to restart your computer and start PWS again and continue the same process. Hopefully everything will be alright now.
Installing IIS on Windows 2000:
              Microsoft Internet Information Server (IIS) is a web server that integrates into the Windows NT Server so no need to download from any where. If you haven't install IIS during installation of Windows 2000, then follow the below steps to install IIS.
 

1. From Start Button, go to Settings and Control Panel.
2. In the Control Panel, select Add/Remove Programs, in that Select Add/Remove Windows Components.
3. In the wizard, check Internet Information Services, click Ok. After this, an Inetpub folder will be created where you can find a folder named wwwroot.

Now your installation process is over. If you want to check whether IIS is running or not, Open Internet Explorer and type http://localhost in the address bar. If everything is working fine, it will display the default page generated by IIS. If not,
 

1. Go to Control panel. Open Administrative Tools and double click "Internet Information Server".
2. Select "Default Web Site" and Click on the Start button present in the toolbar.

Basic file structure of ASP

After installing IIS the web server let us start our first ASP page. Here we assume that ASP engine is working perfectly and server root is set to proper directory were we will keep our fist asp page. Here if the directory path is E:\myfiles\ and our first ASP file name is test.asp then the path becomes E:\myfiles\test.asp. To open this file in web browser mode we have to open this as

http://localhost/test.asp
or
http://127.0.0.1/test.asp

Note that in IIS we have set the default directory to E:\myfiles\

Now with this settings let us go for our fist file test.asp

We will start with our ASP code beginning mark <% and end the code with %> . This way we will tell our ASP engine to execute the ASP part of the code within the <% and %> symbol and send the other codes as it is to the browser. So we will start with telling the server that the code we are going to use is VB Script. ASP is not a script or language , it is a technology server uses. So we have to tell the server which language we are using. We can also use JavaScript as server side script. But mostly VBScript is used for server side scripting requirements and we will also use this. Here is the way we will tell to use VBScript language for processing.
 

<%@ Language=VBScript %>

In the next line we will tell that all the variables used here are to be declared before using. This has some advantage as we move to words developing complex applications using ASP. This is a good practice to follow. So here is our next line

<% Option Explicit %>

After this we will keep our html meta tags and then we will go to the body section of the ASP page. We will try to print the message “Hello World” to the screen. Here we will store this message string in a variable and let us name the variable as msg. Please note that we have told ASP engine that all the variables we use are to be declared before, this we have told in the second line of our code by saying <% Option Explicit %> . So we will declare the variable by using the command Dim. Here is the example

Dim msg
msg=”Hello World”

Now let us print the message or the variable to the screen by using Response.Write object.

Response.Write msg

That’s our entire first ASP example. Here is the complete code.

<%@ Language=VBScript %>
<% Option Explicit %>

<html>
<head>
<title>(Type a title for your page here)</title>
</head>

<body >

<%
Dim msg
msg="Hello World"
Response.Write msg
%>

</body>
</html>

Syntax for declaring variables in ASP

ASP ( VB Script ) provides also easy use of variables but some of the basic syntax is to be followed. One of the biggest advantage of ASP variables is it is not case sensitive. If I declare a variable as my_var then I can still access the same variable by calling it as My_var.

We also have to follow some syntax for declaring variables.

All variables declared must start with a letter. Number or any other key are not accepted as variable. So variable name like 1my_var is not accepted but my1_var is accepted.

Length of the variable name should not exceed 255 characters.

Space period and dashes are not allowed within the variable name.

Reserve words are not allowed. Example we can't declare response as a variable

The best way is to be use descriptive variable names for easy understand of the purpose and identification. Birth date variable should be declared as variable like birth_date

We will use more ASP code and see the use of variables in other tutorials.
 

Getting the variable type and checking in ASP

In ASP we can check what type of ( data ) variable it is before using. We can use the function VarType to display a value for associated with each type of variable. This value is a number so linking this number to type of data is to be done. There is another function TypeName which displays the Data type directly without any associated value.

We can check for a specific type by using the function isArray, isDate etc functions. These are useful while developing code for further processing while working with variables.
Let us start with some syntax of TypeName function.

In the above code we have declared v1 as a variable and assigned a string data to it. So now the variable v1 became string variable. So we will get an output like this by using the above code.

 

We can change the value of v1 to different values and see the type of variable TypeName function returns.

We can create a double variable and check with isArray function to get true or false. Here is the code for this.

 

The output of the above code is shown here.

 

Advantage of using ASP and where to use

ASP is a server side script and it can perform many backend processing jobs for a web site, same way it can't do many things particularly the client end operations as it has no control over the client end events or user controls. So there are many advantages and disadvantages of using ASP to manage web pages. We may not like to say disadvantages of ASP and it is better to say the limitation of any server side scripting language, as these limitations are faced by other scripting languages like PHP, JSP, Perl etc. We will try to understand where ASP can be used and where it should not be used.
 

Using server side scripting language like ASP we can manage the content of any page and such dynamic code ( or content ) for the web browsers can be generated based on various conditions we set in our ASP program. To a visitor the back end script or processing is of no use. They are more interested in design, content, speed etc. So there is no point in asking ASP engine to work when there is simple html content to be displayed at browser end. This will also improve the loading speed of the page. The user browser does not understand scripts we run at server. Brower understands JavaScript (if enabled), html, CSS etc. So what ever output we want to be send to the browser has to be written using these languages. So the task we want to be performed at client end can't be written at server end using ASP.

ASP engine finishes its job of processing the code and then send the codes to users browser. From this point on words till again the page request comes back to server, there is no control of ASP on the page. So we should not expect ASP to perform some tasks which are likely to happen at the client browser end. This will be clear when we discuss some of the task and where ( client or server side ) the task is to be completed and which script will take care of it. There are some tasks we can do at both the ends and the situation on which they are to be used we will try to discuss in next page.
 

Where to use ASP and where not to use ASP

There are many jobs to be performed and we will try to understand what type of job we should do at server end and what we will delegate to client end JavaScript or HTML. Let us start with some tasks we want our web page to do. Here are some of the common jobs we will discuss to get an idea on what to use for different tasks a web page perform.

Displaying Alert message in a small window
Small windows are client side property. So we need Client Side JavaScript to display the alert message. But the content of the alert message we can manage by using ASP. We can conditionally ( display or not ) show the alert box and manage the content ( text part ) based on ASP code we write. So let us conclude that showing an alert message is client side task and we have to use JavaScript for this.

Authenticating user before entering to members only area
This task we can't handle at client end. Once the user enters userid and password, we will verify that using a membership table and then we can say the user is allowed or not. This job is to be handled by ASP script running at server end. Now displaying the welcome message or asking the member to try again is decided by ASP script and the display is shown at browser by using html tags.

Validating data entered by user in a text box ( or form )
This we have seen at many web sites. If we are suppose to enter price in figure and if we enter any character in the text box then we get an error message. Here validation of the data entered by the user is done and accordingly error message is displayed. This task can be done at server side and client side also. Depending on the requirements we can develop the code. There is a risk if we do it at client end only. If script execution is off at client end then the validation code written using client side JavaScript is not going to check and display any error message. This will allow un-validated data to enter into system. However we can check the browser setting of the client computer and display a message or redirect to a page asking them to enable the script execution first before using the form. Depending on server side validation is full proof but for bigger forms large amount of data has to return again from server if data validation fails. This is going to take more time particularly for the visitors with slow connection. So validation is used based on requirements of the page.

We have discussed three common applications here and we will able to understand more on this as we develop scripts for different applications.
 

Different requirement for redirecting users

We redirect the user to different pages or different site based on the condition or based on user selection. We may need different pages to be executed under different conditions. Some time visitor goes to different pages by clicking different links available on the page. But here we will learn how to redirect the user based on our program or our requirement. There can be many reasons to go for a redirection. Here are some of the common reasons for going for a redirection.

Server side form validation
We submit a form with data and we can design a server side form validation to check the user entered data. If the data entered by the user is not in required format or not as per standards then we may ask the visitor to feed the data again. So here we will send back the visitor to the same form page again showing the error message and asking the visitor to try again.

Sending users to different sections based on the permission level
In a portal we may have different areas marked for different types for users and we want the users to go directly to assigned area after they submit their identity ( may be by login ) . Here without any trigger from user end system will redirect the user to a page for there use.

End of a process.
Some time after submitting a data or after a forum posting you want the visitor to be redirected to display a Thank You message. We can have a common thank you page or an error page where we can redirect the browser.

We will discuss header redirection here. Read more on the same topic in PHP section header redirection.

Header Redirection precaution
One main care we have to take care before giving any header redirection is no data to be posted to the user browser before the header redirection command is applied. We can do our script processing and before sending any output to the browser we will redirect the user. Sometime we may not have any output intentionally posted before the redirection but under various condition some time error message the script will return, resulting in error message saying header already send.

Here is the common error message given by ASP engine if header is already sent and script example of header redirection using Response object.

Redirecting user by using response object in ASP

We can do header redirection in ASP by using Response object. Read the basics of header redirection requirements in different condition. Response object takes the url of the site to which the browser is to be redirected. It can be any full URL like http:www. sitename.com or it can be a relative url if within the site. Here is the basic syntax of the Response.Redirect
 

Response.Redirect "http://www.itsyllabus.com/"

We can't apply redirect command if we have already posted any data to the browser. In such a case ASP engine will return error like this .
Response object error 'ASP 0156 : 80004005'
Header Error
redirect.asp, line 15
The HTTP headers are already written to the client browser. Any HTTP header modifications must be made before writing page content.

So we have to take care that our redirection command should work before any data is posted to browser.
 

Printing double quotes in ASP

In ASP VBScript we can't print a double quote inside at output statement. We have to take special care to display a double quote inside or outside a string.

(In PHP we can easily escape the double quote by using escape character ( like \" ) ).

Here are some examples to display double quotes in ASP

We can use chr(34) to print a double quote to the screen

Response.Write chr(34)

( Try different values of chr to display different characters to the screen )

We can use " to print double quotes to the screen
 

Response.Write """
 

Some time within a string we will have double quotes to print. Here to print one double quote we will escape it by one more double quote so two double quotes are to be used. Read this line.
 

Response.Write "Raju told ""ASP is a better scripting language"""

The above line will print

Mark the use of two double quotes within the string to display single double quotes.

Some time we have to display some variable or strings with double quotes within a table cell. Here is a code to display session id inside a table cell.
 

Response.Write "<tr><td>session(""userid"")</td><td>"
 

The output of the above is

session("userid")