University of Virginia 1 Modern Web Application Development Overview of some newer web applications methods Web 2.0 Ajax fundamentals Ruby on Rails

University of Virginia 2 Some Newer Architecture Frameworks  Software Architectures Larger organization of components Frameworks include:  Components we’re given as building blocks  Standard forms of behavior between components Some frameworks for web-based applications  AJAX and supporting frameworks  Ruby on Rails

University of Virginia 3 Some General Issues  Client/Server architectures  Web interface through the browser Client-side processing (Javascript)  Server needs Underlying database management Server side processing  Security, authorization, etc.  Transaction processing  Business logic  Etc.

University of Virginia 4 AJAX and Web 2.0  Have a look at: Ajax: A New Approach to Web Applications, by Jesse James Garrett Building Rich Web Applications with Ajax, by Linda Dailey Paulson. (From IEEE Software.) Book: Pragmatic Ajax: A Web 2.0 Primer (Overview)

University of Virginia 5 Usual Model for Web Apps  Interact with a page Maybe enter info in forms, then hit Submit  Server receives the URL (and forms data etc.) Processes information, and then…  New page is returned to the browser and loaded Even small changes require entire page to be re- loaded  (The web as a hypertext system, not a SW app platform)

University of Virginia 6 New Model: Web 2.0, Ajax  Web 2.0: just a buzzword? See Wikipedia for the history  In part, Web 2.0 is about The web as a computing platform  But also: “new generation” of web usage Collaboration, sharing, things linked together Examples (?):  Blogs, social networking, Flickr, del.icio.us, Skype, games, SecondLife, wikis, podcasts, RSS,…

University of Virginia 7 Ajax  Ajax Named from “Asynchronous JavaScript and XML” Used to refer to two things  Collection of “old” Web-related technologies  A web-based SW architecture  Example apps: Google maps; new Yahoo mail

University of Virginia 8 Ajax Component Technologies  Presentation with XHTML and CSS  Dynamic page display and interaction using the DOM (Document Object Model) in the browser  Data interchange and processing with XML and XSLT  Asynchronous data retrieval with XMLHttpRequest (or equivalent)  JavaScript Ties it all together on the client-side

University of Virginia 9 What’s Different than the Old Model?  Small events Small request to the server that makes small change to the page No refresh of complete page!  Asynchronous processing Browser doesn’t block while waiting Key is a XMLHttpRequest (Javascript to server)  Richer events on the client-side Browser recognizes and shares events much like a GUI-application does

University of Virginia 10 Old vs. New  from Garrett’s web article

University of Virginia 11 Page Modification in Ajax  From Pragmatic Ajax  See explanation given in class

University of Virginia 12 Steps in Previous Diagram 1. Browser requests original page 2. Servers sends back complete page 3. Browser displays and creates a DOM tree 4. (later) Some user activity initiates a request to the server  Asynchronous! To a different URL for a script 5. Server returns data to browser to be handled differently than in (3) above 6. Browser process server-response and updates current DOM in memory

University of Virginia 13 Handling Asynchronous Requests  On the client side with JavaScript An object of type XMLHttpRequest (XHR for short)  On the server side Most basic: any kind of script like those you’ve written before More complex and useful: a larger framework  E.g. servlets, Ruby on Rails, etc. Get request (with parameters) and send back data (not a webpage)  Simple, or more complex (XML)  Note that browsers must be “smarter” too

University of Virginia 14 XMLHttpRequest on the client  What’s it need to do? Be created and used by some JavaScript function Create a request to a script on the server  E.g. a URL with parameters Send it Be linked to a call-back function that will be run on the client when the data is returned

University of Virginia 15 Example: making the call  From the demo (simplified) var xhr = XMLHttpRequest(); // not for older IE xhr.onreadystatechange=callback-func-name; xhr.open(“GET”, “/scriptURL?” + param); xhr.send(null);

University of Virginia 16 Example: Processing Responses  Server talks to the call-back function multiple times xhr.readystate -- an int that indicates status Value of 4 means it’s done and data is ready  Also, xhr.status is set to HTTP response code E.g. 404 “not found”. 200 means “OK”  In call-back function, after checking the above: Get data sent back: xhr.responseText (text data) Process it and update current page using DOM  No reload of entire page occurs!

University of Virginia 17 See demo   Two very simple demos of XMLHttpRequest processing with JavaScript Very simple server-side processing with PHP

University of Virginia 18 Ajax Support  Server-side “remoting” Frameworks and toolkits to support communications more easily  Client-side GUI toolkits for Ajax apps (Java Script)  More complete toolkits for building larger apps Rails, Tapestry, Dojo, Django, … SEAS Final 4 Bracket Challenge  Aptana, includes support for Ajax/Javascript libraries  Used Dojo and Yahoo UI

University of Virginia 19 Ajax and Frameworks  Many frameworks use Ajax and provide Higher-level support for requests and responses Data integration between DBs on the server and client-side objects GUI support Separation of data, control, presentation, business rules “components” or “helpers”: sessions, carts, etc. Internationalization  PHP users: Check out symfony

University of Virginia 20

University of Virginia 21 Ruby on Rails  A framework for developing web apps Remember what a framework is? Rails derived from a real commercial application  Features client-side dynamic pages (DHTML) good integration with database on the server coding written in Ruby based on the MVC architecture AJAX characteristics  Book: Agile Web Development with Rails

University of Virginia 22 Concepts behind Rails  More slogans! DRY: Don’t repeat yourself  Things defined in code in one place only Convention over Configuration  Code less by submitting to defaults  Often depends on naming conventions  Can override these if needed

University of Virginia 23 ORM in Rails  Challenge: putting together an OO program with class design and a set of database tables ORM: object-relational mapping  Rails version of ORM called Active Record Define class and get both Ruby class and DB table Get certain methods for free Other parts of the architecture rely on naming conventions etc. to make all work together with far less programming effort

University of Virginia 24 Rails and MVC Architecture  MVC is a design pattern for interactive applications  Model: just like in Observer Also enforces business rules  View: displays the user-interface  Controller receives external events from the user etc. interact with model and view  Many other frameworks also use MVC E.g. Struts, JavaServer Faces

University of Virginia 25 MVC in Rails Diagram (from book Agile Web Development with Rails)

University of Virginia 26 Views, Controllers in Rails  First step: Rails code generation…  Views: You write HTML pages with embedded Ruby Your code interacts with the controller  Controller: You write code focused on application-specific functions Rails provides  routing events/requests from pages/views to your handlers  sessions, caching, …

University of Virginia 27 Summary  The high-level big picture here is: Certain kinds of applications…  (E.g. web-applications, DB-centered, etc.) … benefit from particular architecture models…  (E.g. Ajax ideas) … and we use frameworks at the architecture level…  (E.g. Rails or AJAX environments) … and lower-level design and coding “tools”  (E.g. specific IDEs, toolkits, GUI libraries,…) … to build larger, better systems quicker.