Building Java Enterprise Applications

The Data Layer

The foundation of any application is the data that it contains and utilizes. Without data, there is no need for an application! Unfortunately, designing a data layer does not produce immediate visible results—no screens appear, no business logic occurs, and management is rarely impressed with entity-relationship diagrams. Because of this, the data layer is often designed and implemented hastily, leaving the rest of the application to suffer and compensate for early mistakes. Instead of taking this precarious approach, this book covers the data layer first and attempts to design it soundly.

In addition to data storage, data access is typically part of the data layer. However, these different functions can be separated from each other; do not be tempted to model your data differently because of a product or technique used in the data access layer. More often than not, the data of an application outlasts the application itself. Data formatted for a specific product or application server may be completely unusable for other products that expect data in a standard format.^[2] Only after the data has been modeled and the storage mediums designed should data access be considered. This section covers databases and directory servers as well as data access methods.

Databases

Once you decide to use a relational database, the number of decisions left decreases quite a bit. First, you must choose a database vendor. Second, the database must be accessible through a JDBC (Java Database ...