J2EE Design Patterns

The Business Tier

There are several ways to slice up a J2EE application. It’s quite common to hear the phrases domain logic, business logic, business object, business tier, and other variants tossed around with wild abandon, resulting in more than a little confusion. What is the business tier? Is the application server part of the business tier, or does it enable the business tier? What about the database? The tables in the database? The servlet container?

All business tiers, as we use the term, have two functions in common. Business tiers:

• Provide a structured model for application data.

• Provide procedures for performing business-related activities.

Most also share the following characteristics. Business tiers:

• Are shared by multiple clients.

• Provide a framework for transactions, ensuring that the information in the domain model remains in a valid state.

• Provide a persistence mechanism for application data.

Most enterprise applications ultimately serve multiple clients, whether different types of clients (servlet applications versus Swing GUIs) or multiple instances of the same type (10,000 Swing GUIs, or an array of web servers). Most applications will use some transaction functionality at least once, but transaction implementations can be done via JTA, EJB, JDBC, or raw objects, depending on the needs and desires of the designer. Persistence is commonly associated with the transaction logic, often via JDBC and a database. Chapter 10 is devoted to transactions and concurrency management, ...