E-Commerce CMM503 – Lecture 8 Stuart Watt Room C2

Summary of this week Learning outcomes –A basic understanding of server-side scripting, and its main differences from client-side scripting –Able to set up a basic site using Microsofts Internet Information Services –A basic understanding of the Active Server Pages object model

Part 1 Server-side scripting and Internet Information Services

1 An overview of server-side scripting

1.1 Why use server-side scripting? When you want to give users access to a database When you want people to be able to share data with each other When you want pages to be dynamically generated, but when you cannot be completely certain that peoples browsers support JavaScript When you want to deliver more complex behaviour than you can with JavaScript When you want to use more processing power to generate the page than you could reasonably expect the user to have

1.2 Main server-side scripting technologies CGI (or: Common Gateway Interface) –Portable, runs outside server, slow PHP (or: PHP: Hypertext Preprocessor) –Portable, good for databases, medium to fast Cold Fusion –Proprietary, portable, good for databases Active Server Pages (or ASP) –Proprietary, Microsoft-specific Java Server Pages (or JSP) –Portable, good for Java code

2 Active Server Pages Solves almost all the problems associated with static HTML and client-side scripting. Advantages –It is simple, you only write your code in the HTML page itself. –No compiling, no complex interfacing, quick and easy to update Disadvantages –Mostly Microsoft-specific (although the Apache clone is very good)

2.1 Active Server Pages (ASP) Are processed in response to a client request –Server-side scripting Are processed by an ActiveX component –A scripting engine Have the file extension.asp Contains HTML tags and scripting code –Scripts are code between VBScript is the most widely used language –You can also use JavaScript, or even Perl!

2.2 ASP ASP provides a server-side scripting environment This includes: –Reading information from an HTTP request –Customising an HTTP response –Storing information about a user –Extracting the capabilities of the users browser

2.3 How does ASP work? Client Server Script processor Request Response

2.4 ASP Vs (D)HTML The main difference between ASP and (D)HTML pages is the location where the script is run. –HTML, DHTML, or client-side script, is run on the client, in the browser, after the page is sent from the server –ASP, or server-side script, is run on the server before the page is sent to the browser. The Web server processes the script and generates the HTML pages that are returned to the Web browser

2.5 Coding: ASP Vs. DHTML Server-side script and client-side script look very similar because they both use the same languages, VBScript, JavaScript, or even Perl. Server side scriptClient side script RGU Home The time here is RGU Home The time here is Document.Write(time()).

2.6 Coding: ASP v DHTML In practice, the extended tag makes them even closer! Server side scriptClient side script RGU Home The time here is <SCRIPT LANGUAGE=JavaScript RUNAT=server> Response.Write(time() ). RGU Home The time here is Document.Write(time() ).

2.7 A Simple ASP Example A Simple ASP Example Simple ASP Example

2.9 Example of an ASP error message Look for the technical information! It will tell you where the error was

2.10 How does ASP work inside? ASP files are compiled into procedures –HTML is turned into a print statement –Other code is embedded directly Advantages –HTML editors (e.g., Dreamweaver) can be used to create ASP pages –Program control flow is applied to HTML –Much improved performance over simpler server-side scripting such as CGI

2.11 ASP pages as procedures First time around: –The ASP file is read from disk –It is then compiled into a program, and a copy of the compiled version kept in a cache Future references to the same page: –Read the compiled procedure and run it immediately

3. Setting up sites using Internet Information Services

3.1 Initial screen for Internet Information Services

3.2 The Internet Information Services control panel

3.3 To create a new virtual directory

3.4 The virtual directory wizard

3.5 The virtual directory wizard

3.6 Setting the default scripting language to JavaScript

Part 2 Active Server Pages Basics of the object model

4. COM objects in one slide Objects consist of: –Properties And fields – these are attributes of the object –Collections Which give you lists of things –Methods Like Document.Write in JavaScript, they ask objects to do things –Events Are a way of keeping track of things happening to objects behind the scenes. Rarely used in ASP, except for sessions

4.1 ASP Built-in Objects Request Response Session Application Server ObjectContext

4.1.1 ASP Built-in Objects Request –Retrieves the values that the browser passes to the server during an HTTP request Response –Controls what information is sent to a browser in the HTTP response message

4.1.2 ASP Built-in Objects Session –Used to manage and store information about a particular user session Application –Used to manage and store information about the Web application

4.1.3 ASP Built-in Objects Server –Provides access to resources that reside on a server ObjectContext –Used to commit or abort a transaction managed by Microsoft Transaction Server (MTS) for ASP pages that run in a transaction

4.1.4 ASP Built-in Objects RequestRetrieve information passed from the browser to the server ResponseSend output to the browser SessionStore information for a specific user ApplicationShare information among all users of your application ServerWork with the properties and methods of components on the server

4.2 What is a collection? A collection is simply a set of objects –They may be Indexed by number (usually from 1, but not always) Indexed by string A collection is an object in its own right –Properties: Count, Item –Methods: Add, Remove

4.3 Request Object Collections ClientCertificate Cookies Form QueryString ServerVariables

4.3.1 Request Object ClientCertificate –The values of the certification fields in the HTTP request Cookies –The values of cookies sent in the HTTP request

4.3.2 Request Object Form –The values of form elements posted to the body of the HTTP request message by the form's POST method Well see an example in a moment

4.3.3 Form Collection Ice cream parlour Name: Favourite Flavour: Mint Vanilla Coffee

Using form collections Access to named fields: Request.Form.Item("name") Request.Form.Item("flavour") Access to the form collection: var myForm = Request.Form; var myCount = myForm.Count; for (my index = 1; index <= myCount; index++) { … }; –See the example: ice_cream_form.asp

Full data recording script Ice cream results Field name Field value <% var myForm = Request.Form(); var myCount = myForm.Count(); for (index = 1; index <= myCount; index++) { %> <% }; %>

4.3.4 Request Object QueryString –The values of variables in the HTTP query string, specifically the values following the question mark (?) in an HTTP request ServerVariables –The values of predetermined Web server environment variables See an example: servervariables.aspservervariables.asp

4.4 Response Object Buffer –indicates whether a response is buffered Expires –Specifies the length of time before a page cached on a browser expires. If the user returns to the same page before it expires, the cached version is displayed

4.4.1 Write method Really important!! –The Write method of Response object adds text to the HTTP response message if (Request.Form.Item("name") == "Stuart") { Response.Write(" No room for you here!"); }; –You can put any data in the parameter you like, but strings are most common

The Write shortcut The Write method is so common theres a short cut: – can be written: – Note that this doesnt end with a semicolon! This is much shorter, and is preferred for simple expressions and values

Write method var myCount = Request.Form.Count; for (index = 1; index <= myCount; index++) { Response.Write(Request.Form.Item(index)); }; ); %> The string returned by the Write method cannot contain the characters %> in an HTML tag, so the escape sequence %\> is used instead

4.4.2 Redirect method Instead of sending content from the response message to the user, the Redirect method of Response object can be used to redirect the user to another URL. The URL specifies the absolute or relative location to which the browser is redirected. <% if (Request.ServerVariables("HTTP_UA_PIXELS") == "640x480") { Response.Redirect("poorscreen.htm"); } else { Response.Redirect("nicescreen.htm"); }; %>

5. Session Tracking and Cookies Enable a web server to distinguish between clients –A server performs session tracking by keeping track of when a specific user visits a site. A unique session ID will be assigned to the user –Cookies are small files sent by an ASP page (or another similar technology, such as a Perl CGI script) as part of a response to a client

5.1 The core of an application: global.asa Defines events for sessions and the application –Events are triggered by a change in the environment function Session_OnStart { Application.Lock(); var visits = Application.Contents("NumberOfVisitors"); Application.Contents("NumberOfVisitors") = visits + 1; Application.Unlock(); };

directives in processing directives –Send information to server about how to process.asp @LANGUAGE is most frequently used –Specifies the scripting language to be used in the.asp file. For example: sets the scripting language to VBScript

7. Summary Active Server Pages versus JavaScript –Server-side versus client-side Easier to access databases and other programs Better control of the scripting environment For more information: –See the documentation installed with IIS: