Patterns and Frameworks for Managing Dynamic Views in Web Applications

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 • Patterns: • 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 • Controller • 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. 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. 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 1-58113-556-4/02/0700 • JavaServer Faces Technology http://java.sun.com/j2ee/javaserverfaces/ • JavaServer Faces - JSR127 http://jcp.org/en/jsr/detail?id=127 • Understanding JavaServer Pages Model 2 Architecture -- http://www.javaworld.com/javaworld/jw-12-1999/jw-12-ssj-jspmvc.html • The Problems with JSP -- http://www.servlets.com/soapbox/problems-jsp.html • The Apache Jakarta Project -- http://jakarta.apache.org/ • Enhydra Barracuda http://barracuda.enhydra.org • 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 http://www.ftech.co.uk/~honeyg/articles/pda.htm • Designing Enterprise Applications with the J2EETM Platform, Second Edition http://www.ftech.co.uk/~honeyg/articles/pda.htm