Java Design Concepts

The Java EE platform makes use of a multi-tiered architecture model for the enterprise applications. The multi-tiered is a server-client architecture where the user interface, the business logic and the data storage is developed as individual modules, most often on different platforms. The enterprise application is then distributed over these tiers and is also developed as individual modules. The three tiers can be described as follows:

• Client Tier - Components that run on the client machine.
• Middle Tier - Components that run on the JEE Application Server.
• EIS Tier - Components that supply information to the system.

Middle Tier
The Middle Tier coordinates the application, process commands, makes logical decisions and evaluations, and performs calculations. It also moves and processes data between the two surrounding layers.

EIS - Enterprise Information System
An Enterprise Information System is generally any kind of computing system that is of "enterprise class" that makes information available to the system. This means the system offers "high quality of service", dealing with large volumes of data and capable of supporting the applications running in the enterprise environment with information.

As can be seen from the figure above, the enterprise application is distributed across the tiers. In a Java Enterprise environment, the client tier consists of the clients' machine. This contains either an application running on his machine, or the dynamic HTML pages that is viewed by his browser on his machine.

The Middle tier consists of two layers. The Presentation Layer contains the web components that run in a web container. This is usually Java Servlets or JSP files. The presentation layer can further be split away from the middle tier and deployed on a separate machine. The Business Layer contains the EJB modules that implement the business logic of the applications. The EJB components are deployed in an EJB container which provides security, transaction management and the ability to scale the application. The EIS tier contains the database which stores the information relevant to the application.

This architecture is the most common type found in most enterprise environments. As mentioned earlier, the presentation layer might in some instances be deployed on it's own machine to increase the scalability of the enterprise solution.

External Information

• Wikipedia