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Chapter 11
 

Chapter 11

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    Chapter 11 Chapter 11 Presentation Transcript

    • Web 101 Third Edition by Wendy G. Lehnert & Richard L. Kopec Chapter 11: Web Pages and Scripting Alternatives
      • Learn what CGI means
      • Find out what Java applets can do and how to add them to your Web pages.
      • Learn how data-driven Java applets make it easier to manage frequent Web page updates.
      • Learn about XML
      • Learn about AJAX and how it works
      • Learn about PHP
      Learning Objectives
      • It’s very easy to add dynamic elements to your Web pages.
      • Ready-made JavaScripts and Java applets are available on the web for you to add to your Web page.
      • A JavaScript is a bit of code written to enhance a Web page.
      • A Java Applet is a small Java program that is attached to a web page.
      Taking Charge
      • A Script is a small computer program written in a scripting language.
      • Scripts can be customized for you at an interactive Web site established for this purpose. (http://www.htmlgear.lycos.com/)
      • You can also download an authoring tool that helps you to do the same thing. (http://www.htmlgoodies.com/)
      • You can visit a freeware site and cut and paste one into your Web page.
      Taking Charge
      • Some Javascript freeware sites (from Chapter 10): http://www. wsabstract .com/
        • http: //Javascript .internet.com/
        • http://www. JavaScriptsearch .com/
      Taking Charge
      • A scripting language is usually more limited and simpler than a full-fledged programming language.
      • Javascript interpreters are built-in to your Web browser, so no additional server support is needed to use it.
      • In addition to Javascript, your Web server might also support PHP or Perl.
      • PHP is a more standardized and potentially easier to use scripting language than Javascript.
      • Perl is another common scripting language.
      • There are also applets , small programs written in Java that can also be used on Web pages.
      Taking Charge
      • Some Web programs are intended to be done on the client computer, but others work best when done by the server.
      • In order to use server-side programs, the client must pass information to the server.
      • The protocol used by the client to pass needed information to the server is known as a Common Gateway interface (CGI).
      • The programs that process this information are known as CGI scripts.
      • Web page hit counters are commonly implemented this way:
      CGI Scripts
      • A hit counter MUST be implemented on a server - Javascript cannot write to storage for security reasons - a rogue Javascript program could do a great deal of damage!
      • The hit count data collected by your computer is sent to a server for storage by the hit counter CGI Script whenever your Web page is accessed.
      • These CGI services are often housed on a 3rd-party computer, so three computers are involved: 1) one hosts the Web browser requesting the page, 2) one stores and serves the Web page, and 3) one offers the CGI service and data storage.
      CGI Scripts
      • To install your own CGI scripts, you need access to a Web server that supports CGI.
      • Because of security concerns, such access is often very limited, if available at all.
      • CGI scripts are often written by programmers for programmers, but there are some that you can try.
      • Live Counter: http://www. chami .com/counter/classic/
      • There are 5 files:
      • 1. a “.class” file (a Java applet)
      • 2. Three “.pl” files (a CGI Perl script)
      • 3. A “.gif” file (images of the counter digits)
      CGI Scripts
      • If your Web server supports CGI, you might consider trying LiveCounter.
      • Besides hit counters, CGI scipts can be used to
        • password protect your Web page
        • store data
        • add a site specific search engine to a web site
      CGI Scripts
    • Java Applets
      • An applet is a small executable program written in Java attached to a Web page.
      • Applets require that a JVM be installed on the client computer.
      • A JVM (Java Virtual Machine) is a platform-specific browser add-on that makes it possible for Web browsers to execute Java applets.
    • Java Applets
      • Java is a full-fledged programming language.
      • Applets pose less of a risk than scripts do.
      • Applets can’t carry viruses since they can’t write to the local machine.
      • Programming Java Applets will require programming skill
      • You can find freely available applets online at applet sites
      • As an applet is software, so it will have a license too
      Java Applets
      • To install an applet:
        • Download and unpack the applet
        • Read all available documentation
        • Insert the required HTML snippet into your Web page
        • Modify the PARAM values as needed
        • Upload your Web page to the server
        • Upload the required .class file
        • Upload any required support files
      Java Applets
      • Data-driven Web page displays are used to minimize the amount of effort needed for ongoing Web page maintenance.
      • A Java applet reads and displays the information contained in a text data file.
      • Only that text file needs to be updated.
      • These applets are often highly customizable
      Data-Driven Web Pages
    • Data-Driven Web Pages
    • Data-Driven Web Pages
      • Data-driven displays are not limited to text.
      • They can accept data from the user.
      • Applets that do this are freely available on the Web.
    • XML
      • Data-driven Web (DDW) sites do not work well with HTML because DDW pages are based on separation of content from presentation.
      • eXtensible Markup Language (XML) is a markup language designed to organize content (the data).
      • XML works cooperatively with CSS to present this content.
      • XML is often called a data description language.
    • XML
      • XML allows the user to define application-specific tags.
      • The user can use these tags to describe how the elements should be arranged relative to each other.
      • A CSS file can be created that describes how to display each of the user-defined elements.
      • An XML-enabled browser could then be used to display the Web page described.
    • XML
      • A sample XML content description:
      • <!DOCTYPE news-list [
      • <!ELEMENT news-list (title, news*)>
      • <!ELEMENT news (header, body, link?)>
      • <!ELEMENT title ANY>
      • <!ELEMENT header ANY>
      • <!ELEMENT body ANY>
      • <!ELEMENT link ANY>
      • ]>
    • XML
      • A sample XML data file:
      • <news-list>
      • <title>Announcements</title>
      • <news>
      • <header>Assignment #4 Due Date Extension</header>
      • <body>The deadline for assignment #4 has been extended to 6pm on Friday, April 5.</body>
      • </news>
      • <news>…</news> // another news element
      • <news>
      • <header>Course Project Assignments for 120</header>
      • <body>These are the course projects for the 9:30 folks.</body>
      • <link>http://www-unix.oit.umass.edu/~lehnert/ assignments.html</link>
      • </news>
      • <news>…</news> // another news element
      • </news-list>
    • XML
      • An associated CSS file:
      • title { font-size: 12pt; font-family: arial;
      • color: red; font-weight: bold;
      • text-align: center; margin-top: 10;
      • margin-bottom: 10; display: block}
      • header { font-size: 8pt; font-family: arial;
      • font-weight: bold; margin-top: 10;
      • margin-left: 6; display: block}
      • body { font-size: 8pt; font-family: arial;
      • margin-left: 6; display: block}
    • XML
      • The final Web page
    • XML
      • XHTML - eXtensible Hypertext Markup Language)
      • Combines HTML and XML.
      • Adds XMLs capability of creating new elements.
      • Most browsers recognize XHTML.
      • A transitional language as the Web pages are transformed from HTML to XML.
    • AJAX
      • Asychronous Javascript and XML.
      • Used to implement Web 2.0 applications (Chapter 4).
      • Formerly known as DHTML (dynamic HTML).
      • Allows browser to carry on additional tasks while it waits for some Javascript action to be completed.
      • Normally, browsers “freeze” until the Javascript task is completed.
      • Permits the creation of shared documents like those found in Google Spreadsheets and Docs.
      • Users can be entering data into a spreadsheet while the Javascript engine is busily dispatching it to the server for distribution to other document collaborators.
    • AJAX
      • Can also send form data to server as it’s entered, eliminating the need for a Submit button.
      • Used to power:
        • Microsoft Outlook Access
        • Google Maps
        • Yahoo! Maps
        • Flickr
        • Netflix
        • Google Docs
    • PHP
      • Newest kid on the scripting block.
      • PHP: P ersonal home page H ypertext P reprocessor
      • Open Source, server-side, scripting language
      • Intended to produce dynamic Web content.
      • Useful for frequently changing data displayed in stable format.
      • Simplifies task of accessing a database with frequently updated data, extracting desired information, and generating a Web page to display it.
    • PHP
      • Server used must support PHP.
        • How to tell? Insert this code into an HTML file: <?php echo “Your server supports PHP” ?>
        • If you see the string appearing in the echo statement above on the web page containing this code, then your server supports PHP.
    • PHP
      • PHP can be used to capture data from a Web page, process it, then generate a Web page to display the result.
      • Example, Punky’s Pizza Parlor
      • A “normal” Web page is created to capture order information:
    • PHP
      • The HTML file uses the ACTION attribute of the FORM element to trigger the PHP code: <form action=“order.php” method=“post”>
      • As you can probably guess, the PHP code to be executed when the SUBMIT button is pressed can be found in the file “order.php”
      • As you can also probably guess, the extension “.php” is used for files that contain PHP code.
    • PHP
      • /* S tart of PHP code */ $pizza = $_POST[‘pizza’]; /* get the pizza type from POST data */ $topping1 = $_POST[‘topping1’]; /* get 1st topping from POST data */ $topping2 = $_POST[‘topping2’]; /* get 2nd topping from POST data */ $topping3 = $_POST[‘topping3’]; /* get 3rd topping from POST data */ $quantity = $_POST[‘quantity’]; /* get quantity ordered from POST data */ /* create HTML page HEAD element */ echo “<html> <head> <title>Pizza Order</title> </head> ”; /* start the BODY element */ echo “<body> <h1>Punky’s Pizza Parlor</h1> <h2>Order Confirmation</h2>”; /* Report the order data */ echo “You ordered a ”. $pizza . “ pizza with ” . $topping1 . “, ”. $topping2 . “, and ” . $topping3 . “.<br>”; echo “Number ordered: ” . $quantity . “ <br><br>”; /* compute and report the cost */ printf(“Your cost, including 8%% tax: $%.2f<br>” , ($quantity*10)*1.08); /* write the date and time of order */ echo “Time ordered: ” .date(‘D, d M Y g:i:s A’) . “ <br>”; /* finish the page */ echo “Thank you for ordering from Punky’s Pizza Parlor!”; echo “</body></html>”; /* end of PHP code */
    • PHP
      • These assignment statements capture the data entered in the Web page form control elements (the selection lists).
      • As you can see, variables in PHP are preceded by a $ sign.
      • All PHP statements end with a semicolon.
      • $pizza = $_POST[‘pizza’]; $topping1 = $_POST[‘topping1’]; $topping2 = $_POST[‘topping2’]; $topping3 = $_POST[‘topping3’]; $quantity = $_POST[‘quantity’];
    • PHP
      • These echo statements begin building the Web page dynamically, writing it to the browser piece by piece.
      • In PHP concatenation is indicated by a period (Javascript uses a +).
      • Strings are indicated the same way - using single or double quote characters as delimiters. echo “<html> <head> <title>Pizza Order</title> </head> ”; echo “<body> <h1>Punky’s Pizza Parlor</h1> <h2>Order Confirmation</h2>”; echo “You ordered a ”. $pizza . “ pizza with ” . $topping1 . “, ”. $topping2 . “, and ” . $topping3 . “.<br>”; echo “Number ordered: ” . $quantity . “ <br><br>”;
    • PHP
      • This statement performs the computation, then prints and formats the results so they look good.
      • The printf statement uses format specifiers: %% (to allow printing of a single %) and %.2f (indicating that a floating point value should be displayed to exactly 2 decimal places)
      • printf(“Your cost, including 8 %% tax: $ %.2f <br>” , ($quantity*10)*1.08);
    • PHP
      • The echo statement uses the date function to print the current date according to its own specific format specifiers (see next slide).
      • The date format specifier used here is D, d M Y g:i:s A
      • produces
      • Sat, 09 Sep 2006 11:23:03 AM
      • echo “Time ordered: ” .date(‘D, d M Y g:i:s A’) . “ <br>”;
    • PHP
      • The date function format specifiers
    • PHP
      • These two statements complete the Web page:
      • echo “Thank you for ordering from Punky’s Pizza Parlor!”;
      • echo “</body></html>”;
    • PHP
      • The Web page produced:
    • How Far Can You Go Without Programming?
      • Quite a ways!
      • You should be able to build functional and attractive Web pages.
      • Numerous scripts and applets are freely available on the Web to enhance your pages.
      • Many are easily incorporated into your Web page.
      • But some may simply not work!
    • How Far Can You Go Without Programming?
      • You can acquire an Integrated Development Environment (IDE) with a Rapid Development Application (RAD) editor which provides Graphical User Interface (GUI) to assist you.
      • You can also hire a programmer to (try rentacoder.com)!
      • Although programming is becoming easier and easier, some coding tasks can be quite challenging even for experienced programmers.