1. Patterns and Frameworks for Managing Dynamic Views in Web Applications
Author: Daniel Archambault
Supervisor: Harold Streeter

2. Overview
Scope of the problem of managing dynamic views in web application
Motivation behind providing better solution for managing dynamic views in web application
Patterns and Frameworks already in use
New Pattern and Framework proposed
Future work

3. Web Application Development Problems
There are several problems being actively researched in web application development, such as:
Managing Dynamic View: determine which view to display and its content with consistent information
Authentication: identify users of a system and decide what privileges to provide to specific users
Error Handling: determining accurately source of error, reporting it appropriately and recovering from it

4. Problem of Managing Dynamic View in Web Application
View and Content of web pages are becoming increasingly complex
Need to decouple the work of the web designer creating views from the programmers providing the content
Need to provide improved web application development framework to facilitate:
View’s components arrangement and reuse
Interconnection between view components state and input handling with object defining application’s behaviors

5. Motivation Generally in commerce:
competition is reducing profit margins
cost of running and maintaining increasingly complex system increases
Very important to minimize costs to avoid losing money
money
profit
cost
time

6. Motivation cont’d Achieving desired set of Quality attributes
Modifiability
Security
Performance
Reliability
Availability
Usability
Patterns and Frameworks facilitate building, maintaining and expanding complex web application by focusing on such quality attributes

7. Relationship between Patterns and Frameworks
Model-View Controller (MVC)
Model 1
Model 2
Patterns within MVC
Front Controller
Mediator
Command
Composite View
Observer …
Frameworks:
J2EE BluePrints Web Application Framework(WAF)
Apache Struts
Apache Turbine
Barracuda
Hammock
SourceForge WebWork
BEA WebLogic
IBM WebSphere …
Building Blocks of

8. Model-View-Controller Pattern
Model-View-Controller (MVC) Pattern
Well established pattern for development of interactive application
Increasingly popular in web application development
Benefits
Separates design concerns (control, presentation, data persistence and behavior)
Decreases code duplication
Centralizes control
Improves application modifiability
Helps construct architecture that facilitates managing dynamic views

9. Model-View-Controller Pattern Structure
Defines application behavior
Maps user actions to model updates
Selects view for response
View Selection
State Change
User Actions
View
Renders the models
Requests updates from models
Sends user actions to controller
Allows controller to select view
Model
Encapsulates application state
Responds to state queries
Exposes application functionality
Notifies views of changes
State Query
Change Notification
Events:
Method Invocations:

10. Enterprise Servers/ Data Sources
MVC Model1 Pattern
Application control is decentralized (current page determines next page to be displayed)
Each JSP page processes its own inputs (parameters from GET or POST)
Request
Browser
JSP
Enterprise Servers/ Data Sources
Response
JavaBean
Application Server

11. Enterprise Servers/ Data Sources
MVC Model2 Pattern
The only difference with Model 1 is the addition of a controller servlet
Dispatch requests from the client tier
Selects views
Response
Enterprise Servers/ Data Sources
JSP
(View)
Request
Browser
Servlet
(Controller)
JavaBean
(Model)
instantiates
Application Server

12. J2EE BluePrints Web Application Framework (WAF)
WAF is a good starting point for learning about the principles of MVC Model 2 based framework design and usage in web application
It is used as the infrastructure of some sample J2EE applications provided by Sun
Demonstrates the mechanism and effective use of a Web-tier framework in an application design
WAF is suitable for small and non-critical application
Features
Front Controller servlet
Abstract action class for Web-tier actions
Templating service
Generic custom tags
Internationalization support

13. Apache Struts Framework
Struts is also based on the MVC Model 2 pattern, but is more powerful than WAF
Industrial-strength framework
Suitable for large application
Struts is not a “standard” for which J2EE product providers can reliably create tools
Struts provides more features than WAF
Web forms with validation
Automatic population of server-side JavaBeans
Utility classes for XML
Richer set of custom tags the ones offered by WAF

14. Apache Turbine Framework
Turbine is similar to Struts, but has richer set of features for managing dynamic view, such as:
Integrates with other template engine than JSP, such as Cocoon, WebMacro, FreeMarker and Velocity
Caching Services (speeds up dynamic web applications by providing a means to manage cached data of various dynamic natures)
Turbine also have a broader scope than struts, providing:
Integration with Object Relational Mapping tools capability
Job scheduler
Localization services
It is based on “Model 2 + 1” which is very similar to Model 2 (main difference is the way the actions are used)

15. Enhydra Barracuda Framework
Barracuda framework is a combination of MVC and Component frameworks
It is more scalable than Struts, since it supports 3 different approach to content generation (accommodate application development with different levels of complexity):
Simple Servlets
Template Engines (JSP, TeaServlet, Webmacro, Freemarker, Velocity)
Document Object Model (DOM) Manipulation
It provides better component composition and reuse than using Turbine or Struts
Barracuda is still not a “standard” for which J2EE product providers can reliably create tools

16. New Framework Proposed: JavaServer Faces
JavaServer Faces intends to handle all of the complexity of managing the user interface on the server
Definition in progress by the Java Specification Request JSR127
To establish a standard API for creating Java web application GUIs
To eliminate the need for developers of creating and maintaining web application GUI infrastructure
To help bridge the gap between conventional GUI toolkit developers and web-based GUI developers
JaverServer Faces will provide a standard GUI component framework which can be leveraged by J2EE development tools providers

17. New Pattern Proposed: Active View
Active View is a new pattern in the area of web application business layer
Intent: Manage a Web active (dynamic) view
Forces:
Increase in demand for dynamic page content
Requirement to update content with consistent information
Need to develop a specific powerful client by using a particular protocol to support communication between client and server.
When data value changes in database, the runtime system produces a particular signal over the net, and upon receiving the signal the client update its view.

18. New Pattern Proposed: Active View cont’d
Solution:
The Active View pattern provides a solution to this problem by refocusing the Observer pattern in a Web architecture
Defines an easy method to develop an application
Renders the front-end receptive to business logic’s signal
Increases the independence among objects, allowing the subject to disregard the number of interested objects
The communication between the subservlet and observlet could be developed using standard potocol such as Java RMI

19. New Pattern Proposed: Active View structure
Subject
+attach(observer)
+detach(observer)
+notify()
<<Httpservlet>>
#doGet()
#doPost()
Observer
+update()
0..*
Observlet * 1
Subservlet
1..*
1..*
Trigger
+SendEvent()

20. Future Work Study more in-depth the Active View pattern
Explore integrating the Active View pattern with other patterns
Provide a reference implementation of the Active View pattern as a proof of concept

21. References
Patterns for Web applications, Diego Bonura, Rosario Culmone, Emanuela Merilli, July 2002, ACM /02/0700
JavaServer Faces Technology
JavaServer Faces - JSR127
Understanding JavaServer Pages Model 2 Architecture --
The Problems with JSP --
The Apache Jakarta Project --
Enhydra Barracuda
Design Patterns: From Analysis to Implementation, Net Objectives, 2002
Design Pattern for Web Programming - Do you need MVC?, Al Williams, June 2002, Internet Strategies for Technology Leaders
The Role of Patterns in Enterprise Architecture
Designing Enterprise Applications with the J2EETM Platform, Second Edition