A Hike Through PostEJB J2EE Web Application Architecture

1
A Hike Through Post-EJB J2EE Web Application
Architecture

• By Konstantin Laufer
• Computing In Science Engineering
• AIP and the IEEE Computer Society
• September/October 2005 Vol. 7 No. 5
• Pgs 80-88
• Presented by Mike Greener

2
Overview

• Paper presents an analysis of a typical J2EE
  Architecture
• Post-EJB refers to technologies that have emerged
  as alternatives to Enterprise Java Beans

3
Overview

• Basic concept of a server-based web application
  has changed little since the mid-nineties
• But, the technologies for developing Web
  applications have grown dramatically
• This is because of growing expectations
• Reliability
• Maintainability
• Extensibility
• Performance
• Scalability

4
Overview - Goals

• Goals for a typical Web application
• Consistent visual styles, layout, and navigation
• Validation
• Component assembly
• OO data model mapped to a relational database

5
J2EE Architecture Blueprint
6
Architecture

• Three Major Tiers
• User Interface
• Middle Tier
• Persistence
• Paper analysis the first two

7
User Interface Tier

• Jakarta Struts Framework
• Controller (configurable servlet)
• Model (domain objects)
• View (JSP pages and JSTL)

8
User Interface Tier - Validation

• Validation
• Java Script
• On the server
• With Struts
• Outside of Struts

9
User Interface - Consistency

• Consistent navigation, layout, and visual styles
• SiteMesh a web page layout and decoration
  framework
• Cascading Style Sheets (CSS)

10
Middle Tier

• Two layers provide greater robustness and
  flexibility
• Service Object Layer
• Data Access Object (DAO) Layer
• POJO (Plain Old Java Objects)

11
Middle Tier - DAO

• DAO Implementation Choices
• JDBC write low level JDBC code
• Object relational mapping (ORM) express mapping
  declaratively
• Entity EJB
• Java Data Objects (JDO)
• Hibernate

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Middle tier Lightweight Containers

• Spring
• Dependency injection or inversion of control -
  connecting the service object and DAO object
• Declarative component assembly - connecting
  various components thru a configuration file (the
  application context descriptor) in order to
  change the applications configuration without
  modifying code
• Hibernate support simplifies code

13
Conclusion

• Article was meant to be an overview a starting
  point for further exploration
• There are many different ways of developing a
  J2EE application
• Very fast pace Struts is only about 5 years old
  and Hibernate is only about 3 years old
• There are competing standards such as Hibernate,
  JDO, and Entity Beans

14
Questions

• Have you used or read about the frameworks
  (Struts, Hibernate, Spring) discussed in the
  paper? If so what is your general opinion of
  them.
• Have you used or read about some other frameworks
  such as .net, XML/XSTL, Velocity, JDO, Entity
  Beans, etc. If so what is your opinion of these.
• Which tier (User interface tier, middle tier, or
  persistence tier) do you prefer to work in and
  why?