An Introduction to J2EE
J2EE is Java, optimized for enterprise computing. Officially J2EE stands for Java 2 Platform, Enterprise Edition. Unlike the traditional Java, which is often used to build client enhancements, J2EE is designed to build server applications. Officially, the J2EE platform is "a set of coordinated specifications and practices that together enable solutions for developing, deploying, and managing" such server applications.
As an enterprise platform, the J2EE environment extends basic Java with tools that "provide a complete, stable, secure, and fast Java platform to the enterprise level."
One goal often stated by developers is that by using J2EE, they're reducing the cost and complexity of creating large-scale solutions. Because Java is a strongly typed language meaning that it requires data types to be used as specified, use of the language is often inherently more secure in Web applications than Web applications built with less strong typing such as C or even PHP and Perl.
Enterprise Architecture
The J2EE platform uses a multitiered distributed application model for both enterprise applications. Application logic is divided into components according to function, and the various application components that make up a J2EE application are installed on different machines depending on the tier in the multitiered J2EE environment to which the application component belongs. Following figure shows two multitiered J2EE applications divided into the tiers described in the following list.
§ Client-tier components run on the client machine.
§ Web-tier components run on the J2EE server.
§ Business-tier components run on the J2EE server.
§ Enterprise information system (EIS)-tier software runs on the EIS server.
J2EE architecture supports component-based development of multi-tier enterprise applications. A J2EE application system typically includes the following tiers:
§ Client tier: In the client tier, Web components, such as Servlets and JavaServer Pages (JSPs), or standalone Java applications provide a dynamic interface to the middle tier.
§ Middle tier: In the server tier, or middle tier, enterprise beans and Web Services encapsulate reusable, distributable business logic for the application. These server-tier components are contained on a J2EE Application Server, which provides the platform for these components to perform actions and store data.
§ Enterprise data tier: In the data tier, the enterprise's data is stored and persisted, typically in a relational database.
Enterprise Application is designed into 6 logical layers, which is related to logic of client tier, middle tier and database tier. It defines which layer belongs to which tier.
§ Presentation Manager
The presentation manager defines the user interface. It always resides on the client tier. It manages the information displayed to the user.
§ Presentation Logic
The presentation logic defines the navigation system of user interface, how and what will be displayed to the user. It may reside the client tier or business tier or database tier based on thin client and thick client and application tier.
§ Application Logic
Application logic defines the actual application logic it with. Application logic can be connectivity, validation etc. It may reside the client tier or business tier or database tier based on thin client and thick client and application tier.
§ Business Logic
The business logic layer contains the business rules of the application. It should be shared with the whole application. It may reside business tier or database tier based on thin client and thick client and application tier.
§ Database Logic
The database logic defines the table structure and the relationship between the tables. It also includes all the constraints of the table. It always reside with database tier.
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