This chapter has introduced the Data Access Object design pattern and defined a set of interfaces that will be used in our 3T application. The DAO design pattern clearly separates the persistence layer operations from the business logic of the application. As will be introduced in the next chapter, this clear separation ensures that the data access layer is easy to test and maintain.

We have also introduced Java Generics as a technique to simplify application design by moving common functionality to an ancestor. The GenericDao interface and the GenericDaoImpl class define and implement methods that will be available free of cost to the extending components. Our implementations also introduced SLF4J, transactional semantics, and working with JPA named queries.

Our journey will now continue with Chapter 5, Testing the DAO Layer with Spring and JUnit, where we will configure a testing environment and develop test cases for several of our DAO implementations.