active server pages in this chapter, you will learn: how browsers and servers interacted on the...
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Active Server Pages
In this chapter, you will learn:
How browsers and servers interacted on the Internet when the Internet first became popular
What first-generation Internet/intranet applications brought to the browser/server relationship
Why Active Server Pages were created
In this chapter, you will learn:
The role of scripting languages
How a Web application works
The role of the Web server
How to create and test a simple Active Server Page application
The relationship between your browser and a distant server was pretty simple
You requested a Web page via your browser, the server received your request, and the server sent back the page that you wanted
Through experience, we learned that the third part of the URL is the folder path, and that it indicates the precise folder on the Web server in which the Web resource is stored
The last part of the URL, specifies the Web resource we requested
As we cruised around, we became very familiar with the following types of resources:
◦Hypertext Markup Language (HTML) documents
◦Graphics
One of the changes that evolved was the first-generation Internet/intranet application
It was an extension to Web servers and was called Common Gateway Interface (CGI)
CGI allowed Web sites to dynamically create Web pages from a program typically written in C or a scripting language such as Perl
CGI added functionality to the Web
CGI programs often exhausted
memory space on Windows
computers
These shortcomings eventually led to
Active Server Pages, or ASP
Active Server Pages (ASP) generate HTML and pass the dynamically created HTML to the browser to be displayed to the user
ASP applications run in a thread, which is the smallest unit of execution of a process
ASP provides a better solution for Web applications in Windows environments than CGI
ASP applications run three to five times faster than their CGI counterparts and can incorporate HTML pages and forms, scripts written in VBscript or JavaScript, and ActiveX components
As Web users became more experienced with ASP, they began running into elements such as the following:
◦ Java Applets
◦ActiveX controls
◦Extensible Markup Language (XML) documents
Active Server Pages create their value through the scripts that they contain
Scripts, or scripting, are lines of code that accomplish a specific task, such as retrieving data from a file
You can mix HTML tags and scripts in an ASP by using a special <SCRIPT>…</SCRIPT> tag
There are two kinds of scripting, client-side and server-side
Client-side scripts download to and execute on the client
Server-side scripts run directly on the server and generate data to be viewed by the browser in HTML format
Most Web users have encountered server-side scripts, even if they weren’t aware of it
You can create client- or server-side scripts in one of two scripting languages:◦ VBScript
◦ JavaScript
◦ JavaScript is a scripting language created by Netscape
Internet Explorer supports both scripting languages
Netscape Communicator supports only JavaScript
The following is an example of a document that contains HTML and a simple VBScript script
The script displays the message “Hello, world!” in a message box<HTML><HEAD></HEAD><BODY><SCRIPT LANGUAGE = VBScript><!--msgbox(“Hello, world!”)//--></SCRIPT></BODY></HTML>
The following is an example of a file that contains HTML and a simple script written in JavaScript
The script displays the message”Hello, world!” in a message box<HTML><HEAD></HEAD><BODY><SCRIPT LANGUAGE = JavaScript><!--alert (“Hello, world!”)//--></SCRIPT></BODY></HTML>
The following HTML page includes a simple server-side script written in VBScript as shown on page 6 of the textbook
Code Dissection◦ A Web page can contain HTML tags along with scripts◦ The line <SCRIPT LANGUAGE = “VBScript”
RUNAT=“Server”>…</SCRIPT> tells the Web server that this script runs on the server first, before the HTML page can be transmitted to the client
◦ The line <SCRIPT LANGUAGE=“VBScript”>…</SCRIPT> tells the Web server that this script should be transmitted to the client and tells the browser to run this script on the client, rather than on the server
◦ The <%…%> tag combination tells the Web server to run the script on the server and pass the results to the client
The following HTML page includes a simple server-side script written in JavaScript as shown on page 6 of the textbook
Code Dissection◦ A Web page can contain HTML tags along with scripts◦ The line <SCRIPT LANGUAGE’”JavaScript” RUNAT=
“Server”>…</SCRIPT> tells the Web server that this script runs on the server first
◦ The line <SCRIPT LANGUAGE=“JavaScript”>… </SCRIPT> tells the Web server that this script should be transmitted to the client and tells the browser to run this script on the client, rather than on the server
◦ The <%…%> tag combination tells the Web server to run the script on the server and pass the results to the client
A Web application is a special type of Web site that contains pages of static HTML and server-side scripts that interact with a user
The Web applications that you will encounter in this book share some common attributes
Programmers routinely use objects to create reusable code that can be used in many applications
You can “trim” the size of an online image, by changing the appropriate property
Objects also have methods Properties and methods are useful, but
the fun starts when an event, the other main component, enters the scenario
An event occurs when a stimulus affects an object
Events create or modify an object Once the Application object is created, an
event called Application_OnStart starts, in the Global.asa file in the Web application directory
Global.asa is a file that contains events that are activated when Application and Session objects are created and when they are destroyed
An Application object’s main job is to store any settings that are the same between sessions
Sessions are special environments that the Web server creates for each user of an application
The sessions themselves are also objects One is created at the same time that the
Application object is being created
The Session object contains the environment in which the user interacts with the application
When the user fills in the form and clicks the Submit button, this event results in the creation of a Request object
Once the server receives the Request object, it begins to respond to the request, resulting in the creation of a Response object
The Application, Session, Request, and Response objects are the most important objects in ASP
PWS is a Web server that allows you to create and test applications in Windows 98, Windows 2000, and Windows XP
Once you complete your Web application and want to use it over the Internet, you use IIS (Internet Information Server)
PWS is designed only as a development environment to be used to create and test Web applications
You must adapt to and use a Web server’s existing folder structure
To create a PWS virtual directory—look for the Personal Web Server and look for Personal Web Manager◦ Verify that web publishing is on and click on Advanced icon
—the advanced directory dialog box opens◦ Type in the name of your directory and then type in the full
pathnname to the directory (http://localhost/Yourdirectory/register.htm )
To create the Register.htm page use the steps on pages 10 and 11 of the handouts
Many text editors such as Notepad attach their own filename extension (.txt in Notepad) to a saved file
Verify that your file does not include a double extension
To create the Register_me.asp script in the VBScript language follow the directions on the page 12 in the handouts
Code Dissection
◦ The line <%@ Lnaguage=VBScript %> specifies the scripting language being used. The <%….%> tells the Web server that the enclosed script code must run before the Web page is transmitted to the browser
◦ The line <% Response.Buffer = True %> tells the Web server to create the entire Web page in memory before sending it to the client
◦ The line <%=Request.Form(“txtFirstName”)%> tells the Web server to insert the contents of the form element txtFirstName
The next step in developing a Web application is testing what you have created
To test the new application refer to the procedures on page 13 in the handouts
This sample application is actually an information system; it receives input, processes the input, and provides output
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Web pages used to be simple items. You requested a page, the server processed your request, and you then received the page for viewing
After simple static Web pages, the industry moved on to utilize CGI scripts, even with their shortcomings
The term script, or scripting, refers to lines of code that accomplish specific tasks, such as retrieving data from a file
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In programming, objects are discrete entities with two main characteristics:
◦ Properties
◦Methods
Properties are the data that describe an object
In this class, you will either use Personal Web Server (PWS), or IIS