Dynamic Web Programming

1
Dynamic Web Programming

• Dr. Hsiang-Fu Yu
• National Taipei University of Education
• Original by Andy Powell

2
Overview

• Dynamic Interactive
• Web Form
• Common Gateway Interface (CGI)
• Server-side programming
• Perl, PHP, ASP
• Client-side programming
• Javascript, Java
• Database connectivity
• Security

3
Why interact?

• Registration and requests for information
• User feedback
• Dynamic information
• Particular services might want to solicit
  contributions from people

4
Simple Web form

• lthtmlgt
• ltheadgtlttitlegtsimple formlt/titlegtlt/headgt
• ltbodygt
• ltform name"simpleForm" methodget"
  action"simpleHandler.cgi"gt
• Your email address
• ltinput type"text" name"email"gt
• ltinput type"submit" value"Submit"gt
• lt/formgt
• lt/bodygt
• lt/htmlgt

5
Interacting With Web Forms

• Steps
• Validate user input
• Process user input
• Generate a response
• These three steps may be done within
• the Web browser (client-side) or
• the Web server (server-side) or
• some combination of both

6
Common Gateway Interface (CGI)

• Mechanism for a Web browser to send data to a Web
  server
• Allow browser to submit data to a program running
  on the server
• Program is often called a CGI script, typically
  written in Perl, PHP or ASP
• Or an execution binary file, compiled from a
  programming language such as C

7
CGI (cont.)

• Used primarily for form submission
• Also be used to upload local files
• CGI URLs often contain ? and characters
• Output from CGI usually dynamic and therefore not
  cached

8
CGI (cont.)
9
CGI Programming - Perl

• Perl - Practical Extraction and Report Language
• Developed as general purpose (UNIX) utility
• Freely available on all platforms (though most
  often used under UNIX)
• Very good at manipulating textual data
• Interpreted - so fast development cycle
• A new Perl process is started for each new CGI
  script, so can be heavy on resources
• Many modules are freely available. See CPAN
  ltwww.cpan.orggt

10
What do I need to do

• Install Perl (if you have a UNIX box, it is
  already installed.)
• Install at least the CGI.pm Perl module from CPAN
• Configure your Web server to recognise files
  ending in .pl (and .cgi) as Perl programs
• Buy one of the OReilly Perl books
• Visit ltwww.perl.orggt and ltwww.perl.comgt for
  tutorials, tips, and example code

11
CGI Programming - PHP

• PHP - originally stood for Personal Home Pages
• C-style language
• HTML embedded scripting language
• PHP commands are embedded into the HTML page
• Hidden inside HTML comments
• Freely available - ltwww.php.netgt
• Lots of code available

12
CGI Programming PHP (cont.)

• Tight integration with databases - particularly
  with MySQL
• Quick development time for database driven
  applications
• Available under UNIX and Windows

13
What do I need to do

• Install PHP
• Configure Web server to recognise files ending in
  .php, .php3 and .php4 as PHP-enabled pages
• Buy the OReilly PHP book!
• Visit ltuk.php.netgt and ltwww.phpwizard.netgt for
  tutorials and sample code

14
CGI Programming - ASP

• ASP - Active Server Pages developed by Microsoft
• HTML embedded scripting language
• bundled in with MS Web server, e.g. IIS
• Free and commercial UNIX version available
  (though not sure about compatibility)
• GUI development tools available

15
What do I need to do

• If you are using Microsoft Web server, it should
  all be ready to go.
• If you are using a UNIX-based server, use Perl or
  PHP.
• Check your Microsoft documentation
• Visit ltwww.learnasp.comgt

16
JavaScript

• A browser programming language developed
  originally by Netscape
• Simple language - not Java
• Object-oriented approach
• Embedded into HTML Web page between ltscriptgt and
  lt/scriptgt tags
• Can also ltlinkgt to external JavaScript file

17
JavaScript and Forms

• JavaScript typically used in combination with
  forms to validate input
• Simple event model, e.g.
• Use onChange or onClick methods to validate
  input before sending data to server-side CGI
  script
• Check that email addresses have _at_ in them
• Check that numbers contain only digits
• Check that mandatory fields are filled in

18
What do I need to do

• Nothing to install! JavaScript is supported by
  the major graphical browsers.
• Buy the OReilly JavaScript book.
• Visit ltwww.javascript.comgt
• Warning - if you enhance your Web forms using
  JavaScript, make sure that they still work if
  JavaScript is disabled in the browser.

19
Java

• Developed by Sun - not standardised
• Supposedly write-once/run anywhere, supposedly
  secure
• Applications - stand-alone
• Applets - embedded into browser
• Interpreted by the Java Virtual Machine (JVM)

20
Java (cont.)

• Applets have not taken off widely
• Inconsistencies between JVM implementations
• Resource requirements
• Can be embedded into server-side applications -
  Java Server Pages
• Good support for database connectivity
• Good GUI development environments available

21
What do I need to do

• Install Java 2 SDK (Software Developers Kit)
• Try it by hand-coding using text editor initially
• Buy one of the OReilly Java books.
• Visit ltjava.sun.com/docs/books/tutorial/gt for
  introduction to Java

22
Database Connectivity

• Data from a Web form is
• processed directly and used as basis for response
  to users
• e-mailed to someone for further processing
• saved to a file (for further processing)
• processed/stored in a database

23
Open Database Connectivity (ODBC)

• Developed by Microsoft
• Generic interface to databases
• A CGI script developed using ODBC and SQL should
  work against any SQL database that offers an ODBC
  driver
• Oracle, MS-Access, MySQL
• Perl, PHP and ASP all offer access to databases
  via ODBC

24
Security

• Web sites that offer interaction through CGI
  scripts are inherently a little more insecure
  than sites that dont
• Watch out that
• Critical files cant be downloaded or overwritten
• Other programs cant be uploaded or started
  unintentionally

25
Using Cookies

• Remember preferences using cookies
• Usually user name and password
• cookies are small chunks of information that
  are stored in the browser but shared with the
  server
• Developed by Netscape but widely adopted
• Cookies should be only shared with the server
  that set them
• Support for cookies in Perl, PHP and ASP

26
Summary

• It is useful to know these basics
• Dont need to develop all the CGI scripts
  yourself
• Products like Microsoft Frontpage come with
  bundled suites of CGI utilities.
• Use externally hosted services
• Build on whats already out there - chances are
  that someone has already developed the CGI script
  you need