Designing and Building a complete EJB3/JPA Application (Part I)

By : Omer Guinko

Published Date : February 16, 2010

The Business Problem
OG News Management System (or OG-NMS) is a news and article management application that provides a framework for specific users to manage news and articles

The OG-NMS at its very basic provides an environment that allows the following:

1. News editors can add an article to the database at any time, with the option to delay publication until a specified release date. Additionally the person submitting the article must be able to specify an expiration date, after which the article will be automatically retired. If these dates are not specified, then the article should be immediately published and remain active indefinitely.
2. Articles can have an approved status, to allow the news editors to control the content, apply any required modifications, and finally approve the articles for publishing once they are ready.
3. The system must track who originally submitted an article or news item.
4. There can be multiple categories, enabling articles to be organized by category. Each category should have a description and an image that graphically represents it.
5. There should be a page with the available categories as a menu. Each category should be linked to a page that shows a short abstract for each published article. By clicking on the article's title the user can read the whole text.
6. News Readers may subscribe to receive intermittent newsletters from OG-NMS

Scoping the Technical Requirements
While meeting OG-NMS's requirements we would like to develop an extensible infrastructure that we can add to in the future. That means making the right abstraction to loosen the coupling between our components.

We should be able to plug-in a different implementation of any part of the system with very few modifications. Our deployment will be partitioned into three tiers:

• The Presentation Tier - involves one or more web servers, each responsible for interaction with the end-user. It reads in and interprets the user's selections and makes invocations to the Business Tier's EJB components.
  The implementation of the Presentation Tier uses Servlets and JSP technology.
• The Business Logic Tier - consists of multiple EJB components running under the hood of an EJB container or Server. These reusable components are independent of any interface logic. The Business Logic Tier is made up of Session beans and Message-Driven beans that realize the Business Logic. Entities implement the Data Access Layer.
• The Data Tier - is where our permanent data stores reside. The database aggregates all persistent information related to OG-NMS site.

The major EJB components in OG-NMS System

OG-NMS Context Diagrams and Actors
The following is a list of all actors interacting with the OG-NMS application:

• News Editor - A user of the system who is responsible for posting news and articles
• System Administrator - A special user of the system who is responsible for maintaining the profile information and setting up the access rights for the other users.
• News Reader - Represent the end user of the OG-NMS online site. The news reader can browse and read the content of the articles and news.