Web Application Programming

1
Web Application Programming

• Carol Wolf
• Computer Science

2
Three tiers and their languages

• Client Server Database
• Html Java, Ruby SQL
• JSP, ERB Visual Basic
• JavaScript PHP, Perl
• Python

3
MVCModel, View, Controller

• Model - Database
• Requests sent using SQL, Structured Query
  Language.
• Response is either an array of data or a
  confirmation.
• View Web page
• Requests sent using Html or embedded programming
  code (JSP, ERB, ASP)
• Controller Program on server
• Sits between the model and view.
• Receives requests from the view, sends them on to
  the model and sends a response back to the view.
• Most critical software and trickiest to write.

4
HTTPHypertext Transfer Protocol

• Http is a stateless protocol.
• Stateless means that nothing is remembered.
• Once a response has been sent, the server forgets
  where it went.
• Request
• Requests are sent by the client to the server.
• They can either be requests for a new page or
  involve a form with parameters.
• Response
• The server sends a response page in return.
• It might be a linked page or data retrieved from
  a database.

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Methods

• Get
• Used for simple requests.
• Parameters are sent in the URL string.
• http//localhost3000/library/find? title
  "Oliver Twist"
• Post
• Parameters are sent within the packet.
• Used when there are many parameters or when
  security is an issue.
• Rails uses only post when there are parameters.

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Action

• The action contains the URL of the server and the
  server program to be executed.
• The URL comes before the question mark and the
  parameters after.
• Example of a URL string
• http//localhost3000/library/find? title
  "Oliver Twist
• http is the connection protocol.
• localhost3000 is the name of the server and the
  access port on the server.
• library/find gives the directory (library) for
  the server program and the program (find) to use
  in that directory.

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HTML Forms

• Forms consist of data fields and a submit button.
  They can also have links to JavaScript code and
  formatting tags.
• ltform method"post" action"http//localhost3000
  /library/find"gt
• ltpgt
• ltbgtBook Titlelt/bgt
• ltinput type "text" name"title" value ""
  size 20 /gt
• lt/pgt
• ltpgtltinput type "submit" value"Find a Book
  /gtlt/pgt
• lt/formgt

8
This shows an html table containing three forms.
The form in the center is the one on the previous
slide.
9
Programming Languages

• Java uses Java servlets, Java Server Pages
  (JSP) and Java beans.
• Ruby on Rails uses ruby programs and Embedded
  Ruby (ERB).
• Visual Basic Uses VB programs and Active Server
  Pages (ASP).
• Others
• PHP (Personal Home Page originally)
• CGI (Common Gateway Interface)
• Perl (Named after the parable of the pearl)
• Python (Named for the Monty Python skits)
• Tcl (Tool Command Language)

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Java

• Developed by James Gosling at Sun Microsystems in
  1991.
• Java servlets on the server control the flow
  between the client and the database.
• JSP (Java Server Pages) can be embedded in the
  html on the web page. They are compiled into
  servlets before they are executed.
• Java server pages are connected to Java beans on
  the server. The beans handle the requests and
  responses.

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Ruby on Rails

• Ruby was developed by Yukihiro Matsumoto in 1993
  and publically released in 1995.
• It is a scripting language and is fully object
  oriented.
• It combines Perl syntax with Smalltalk-like
  features.
• It is said to follow the principle of least
  surprise.

12
Ruby on Rails

• Rails was developed by David Heinemeier Hansson
  and released as open source in July 2004.
• It is based on the MVC (model, view, controller)
  pattern.
• Programmers work on a higher level than with Java
  servlets.

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Rails

• Rails relies on a number of conventions.
• JSP and Java beans have some conventions, but
  rails has a lot more.
• Rails translates commands into SQL, saving
  programmers many hassles.
• Some boiler plate is stored separately and
  added to web pages when required.
• This includes web page headers, CSS (Cascading
  Style Sheets) and JavaScript.
• Database modifications are systematically handled
  by migrations. These are ruby programs that
  when executed change the database.

14
Servers

• The principal open-source server is Apache,
  hosting 49 (June 2008) of all web sites.
• There are many modified versions.
• Apache Tomcat used for JSP and Java beans.
• Google Web Server (GWS)
• IBM WebSphere
• Microsoft Internet Information Services (ISS) is
  the main proprietary server, hosting 35.4 of all
  web sites.

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Databases

• Most databases use the relational model,
  developed by E. F. Codd in the 1960s and 70s.
• Data is stored in tables with rows and columns.
• Queries are usually made with SQL.
• Microsoft has Access for Windows computers.
• MySQL is open source and has more than 11 million
  installations world-wide.
• Oracle is a widely used proprietary database
  developed by the Oracle Corporation.
• Rails comes with sqlite3.
• There are many more.

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Connecting to a database

• Most databases are standalone programs and so
  require that each time they are accessed, you
  must set up a new connection.
• For Java, the connection is sun.jdbc.odbc.JdbcOdbc
  Driver
• Odbc stands for open database connection, and the
  J in Jdbc is for Java.
• Odbc is a protocol from Microsoft that is based
  on the X/Open SQL specification.
• InstantRails comes with SQLite3. It is part of
  the application and does not require a new
  connection for each query.

17
Web Browsers

• The first web browser was Mosaic, released in
  1993. It was developed by the NCSA, National
  Center for Supercomputing Applications. It
  turned into the Netscape Navigator and was
  discontinued by AOL in 2007.
• Microsofts Internet Explorer is the most widely
  installed browser with around 73 of market share
  world-wide.
• Firefox from the Mozilla Foundation has around
  19 of the usage share (August 2008).
• There are a number of other browsers, including
  Safari for Macs with a market share around 6.