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Friday, October 9, 2020

Multitier Architecture

One of the recurring themes that you’ll run into with Java EE is the notion of supporting applications that are partitioned into several levels, or tiers. That is an architectural cornerstone of Java EE and merits a little explanation. If you are already familiar with n-tier application architectures, feel free to skip ahead. Otherwise, the overview presented here will be a good introduction or review that will help lay the foundation for understanding the rationale behind much of Java EE’s design and the services it provides.

If you think about a software application composition, you can break it down into three fundamental concerns, or logical layers:


• The first area of concern is displaying stuff to the user and collecting data from the user. That user interface layer is often called the presentation layer, since its job is to present stuff to the user and provide a means for the user to present stuff to the software system. The presentation layer includes the part of the software that creates and controls the user interface and validates the user’s ctions.

• Underlying the presentation layer is the logic that makes the application work and handles the important processing. The process in a payroll application to multiply the hours worked by the salary to determine how much to pay someone is one example of this kind of logic. This logical layer is called the business rules layer, or more informally the middle tier.

• All nontrivial business applications need to read and store data, and the part of the software that is responsible for reading and writing data—from whatever source that might be—forms the data access layer.

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