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Web frameworks


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Web frameworks: web development done right. …

Web frameworks: web development done right.

Lecture of Web Technologies, University of Naples Federico II

Main topics:
- Evolution of Web Technolgies
- Web frameworks and Design Principles
- Django and Google App engine: web frameworks in Python

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  • 1. Web Frameworks web development done rightCourse of Web TechnologiesA.A. 2010/2011 Valerio Maggio, PhD Student Prof.ssa Anna Corazza
  • 2. Outline 2► Web technologies evolution► Web frameworks ○ Design Principles► Case Study ○ Django and GAE (Google App Engine)► Working Example
  • 3. Intruduction 3► Nowadays frameworks has become a buzzword ○ Software framework ○ Web framework ○ Development framework ○…► So, what do you expect a web framework is?
  • 4. 1. Web Technologies Evolution 4
  • 5. Web: Evolution Roadmap 1 5 HTML Pages HTML Pages:►Web developers wrote every page “by hand”►Update a web site means editing HTML►“redesign” involved redoing every page ○ One at a time►Solution not scalable
  • 6. Web: Evolution Roadmap HTML Pages 2 6 CGI Scripting CGI – Common Gateway Interface► (+) Pages intended as resources ○ Pages are generated dynamically on demand ○ Raise of (so called) server side technologies► (-) Code reuse difficult ○ Lot of “boilerplate” code► (-) High learning curve
  • 7. CGI Perl Example 7► What are pros and cons of these two CGI examples ?
  • 8. Web: Evolution Roadmap CGI Scripting 3 8 HTML Pages PHP like languages PHP like solutions► (+) Learning curve extremely shallow ○ Code directly embedded into HTML► (-) No security and/or protection mechanism provided► (?) Bunch of HTML, (Business Logic) Code, (Data) SQL code all together
  • 9. JSP Example: Pros and Cons ? 9
  • 10. Web: Evolution Roadmap PHP, ASP, JSP, ... 4 10 HTML Pages CGI Scripting RIA and “Integrated solutions” RIA and “Integrated Solutions”► RIA: Rich Internet Applications ○ Q: Do you know what RIA means? ○ A: Desktop-like web applications ● (Ajax and javascript intensive web apps)► A.k.a. Solutions battery included► CMS and Web Frameworks
  • 11. CMS: Content ManagementSystem 11► Aim to manage work-flows and contents in a collaborative environment► Designed to simplify the publication of contents to web sites and mobile devices► Examples: Joomla, Drupal, Wordpress, ….
  • 12. Web frameworks 12► Aim to alleviate the overhead associated with common Web development ○ Databases, templates, sessions, …► Designed to support the development of dynamic websites, web applications and web services► Examples: Struts, Spring, Ruby on Rails, Django, Google App Engine, ...
  • 13. So, What is a Web Framework? 13► What does this code do?► What happens when multiple pages need to connect to database?► Should a developer really have to worry about printing the Content-type?► Is this code reusable in multiple environments with different DB connection parameters?►What happens when a web designer have to redesign the page?
  • 14. Web Frameworks in a nutshell 14► These problems are exactly what a web frameworks tries to solve► Web frameworks provides a programming infrastructure for applications► Focus on developing code without having to reinvent the wheel
  • 15. 2. Web Frameworks Design Principles 15
  • 16. CGI Architecture Model 16 Presentation and Business Logic Visualization Data and Models
  • 17. CGI Architecture Model 17► Task centric architecture (a.k.a. Model 1) ○ Difficult reusability and maintenance of code ○ Requires different skill-sets High coupling among:► Presentation (View) ○ How to show data► Processing (Controller) ○ What information to show► Data Acquisition (Model) ○ What information to extract (from DB)
  • 18. Model 1 Architecture (Java) 18 ► Processing delegates as JSP and Servlets ► Is there any difference between CGI and Servlet?
  • 19. MVC Architecture Model 19 ► Model: ○ Manages domain and data acquisition ► View: ○ Manages the visualization of data ► Controller: ○ Manages domain and data processingQ: Do you think this model is feasible to be used on the web as is?
  • 20. Web-MVC Architecture Model 20 ► Model: ○ Manages domain and data acquisition ► View: ○ Manages the visualization of data ► Controller: ○ Manages domain and data processingA: No (direct) relationship between the view and the model
  • 21. Model 2 Architecture (Java) 21 ► Model: ○ EJB and Javabeans ► View: ○ JSP and JFaces ► Controller: ○ Servlets
  • 22. Fulll-stack web frameworks 22► From wiki: [..] frameworks provide support for a number of activities such as interpreting requests, producing responses, storing data persistently, and so on. [..] those frameworks [..] are often known as full- stack frameworks in that they attempt to supply components for each layer in the stack.► So, what are such components?
  • 23. Web Frameworks Capabilities 23► View ○ JavaScript Library ○ Template Engine and View Composition ○ Development Server► Controller ○ URL Routing ○ Controller-view Association► Model ○ Database Abstraction ○ ORM (Object Relational Mapping)
  • 24. Database Access 24► Distributed Access Logic (JSP, Servlets) ► Centralized Access Logic► Q: How easy is modify the db schema?
  • 25. Active Record pattern 25 ► An object encapsulates both data and behavior ► Put data access logic in the domain object
  • 26. Heavy-weight vs Light-weightFrameworks 26► Heavy-weight frameworks: ○ (Mostly) Java Based ○ Based on Model 2 Architecture ○ High learning curve ○ Bunch of (XML) Configuration Files► Light-weight frameworks: ○ Convention over Configuration and DRY Principles ○ Shallow learning curve ○ Use of Dynamic Languages ● Python, Ruby, Groovy, Scala
  • 27. H-W Java frameworks: Struts 27
  • 28. H-W Java frameworks: Hibernate 28
  • 29. Design Principles 29► Convention over configuration ○ “Convention over Configuration is a programming design that favors following a certain set of programming conventions instead of configuring an application framework. [...]”► DRY (Dont repeat yourself) ○ “DRY is a principle that focuses on reducing information duplication by keeping any piece of knowledge in a system in only one place.
  • 30. 3. Case Study: Django andGoogle App Engine 30
  • 31. Frameworks and Languages 31
  • 32. Python Programming Language 32“Speed and flexibility of development are critical.Dynamic languages let you get more done with less linesof code (which means less bugs)” ► Object oriented languages ► Clean and simple syntax ○ Strong Typed ○ Dynamic Typed
  • 33. Python Programming Language 33► Is there someone that uses python in professional projects? ○ IBM, Google, Sun, HP, Industrial Light and Magic, NASA, Microsoft► Goggle it: ● python ● Youll get more than 9 thousands results
  • 34. Python:Language of the year 2010 34Programming language Python has become programminglanguage of 2010. This award is given to the programminglanguage that gained most market share in 2010.Python grew 1.81% since January 2010. This is a bit morethan runner up Objective-C (+1.63%).Objective-C was favorite for the title for a long time thanksto the popularity of Apples iPhone and iPad platforms.However, it lost too much popularity the last couples ofmonths.Python has become the "de facto" standard in systemscripting (being a successor of Perl in this), but it is used formuch more different types of application areas nowadays. Source: tiobe.comPython is for instance very popular among web developers,especially in combination with the Django framework.Since Python is easy to learn, more and more universities areusing Python to teach programming languages.
  • 35. TIOBE: Programming Languagesranking 35
  • 36. Python Dynamic Typing 36 “Duck Typing” def half (n): return n/2.0 Walks like a duck? Quacks like a duck? Q: What is the type of variable n? Its a duck!
  • 37. Django web framework 37Design characteristics► Model-View-Controller for the Web► Written in Python► Explicit instead of implicit► Loose Coupling► Dont repeat yourself
  • 38. Django Architecture Model 38► Django is based on a slightly different version of MVC ○ a.k.a. MVT: Model View Template► Model: Domain Objects ○ Python Classes► View: contains business logic for the pages ○ Callback as python functions► Templates: describes the design of the page ○ Template Language HTML based
  • 39. Django Stack 39► Database wrapper (ORM)► URL dispatcher► Template system► Admin Framework► I18n & l10n► Authentication► RSS► .....
  • 40. Projects and Applications 40► Projects: ○ Composed by different applications ○ Glued together by unique configuration file► Applications: ○ Set of portable functionalities ○ Code is more reusable ○ Django Plugables ● (
  • 41. URL Dispatcher 41► Loose coupling principle between URLs and Views ○ Based on regular expressions
  • 42. Template Language 42► Very restrictive specific-language ○ Allows only presentation operations ○ No logic and/or processing allowed► Less Pythonic ○ Oriented to web designers ○ HTML based► Templates Inheritance Mechanism ○ Code Reuse
  • 43. Template Language (2)► Template Inheritance 43 ○ Templates are composed by Blocks
  • 44. Template Language (3) 44► Variables: {{ variable_name }}► Tags: {% template_tag %} ○ Board definition: Tags tell the framework to do something► Filters: {{ variable|filter }} ○ Alters the formatting of variables
  • 45. Django Admin Framework 45►So called Killer-application►Compliant with Active record Pattern
  • 46. Django Included Apps 46► django.contrib.auth ○ An authentication system.► django.contrib.contenttypes ○ A framework for content types.► django.contrib.sessions ○ A session framework.► django.contrib.sites ○ A framework for managing multiple sites with one Django installation.► django.contrib.messages ○ A messaging framework.
  • 47. Google App Engine 47► dynamic web serving (built on top of Django) ○ e.g. supports Django Templating Language► persistent storage► automatic scaling and load balancing► APIs for authenticating ○ using Google Accounts► a fully featured local development environment► scheduled tasks for triggering events at specified times and regular intervals
  • 48. References: Google App Engine 48►
  • 49. References: Django 49► ○ Sito del Progetto►!forum/django-it ○ Google group Italiano di Django
  • 50. References: Python 50► ○ Sito ufficiale di Python► ○ Sito ufficiale Python Italia►!forum/it.comp.lang.python ○ Google group Italiano di Python► ○ Forum (~)official Python Italia► ○ Python Italian Conference ○ EuroPython 2011 – Florence, IT – across spring
  • 51. References: Titles 51 ► The definitive guide to Django A. Holovaty and J.K. Moss, Apress
  • 52. References: Titles 52 ► Sviluppare applicazioni web con Django, Marco Beri,APOGEO
  • 53. References: Titles 53 ► Python, Marco Beri, APOGEO Serie Pocket
  • 54. References: Titles 54 ► Programming Google App Engine, D. Sanderson,OReilly
  • 55. And last... 55►Want to get some actions?►Lets do together a working example