１、Building non-trivial web applications with Java is no trivial task.
２、where the business logic will reside
３、how to enforce a consistent design across all application layers
４、Each application layer should be isolated from other layers but allow an interface for communication between them.
５、Assembling a model that can be presented in a view.
６、 type coupling
７、“allow”的使用： In particular, the Hibernate framework allows object-to-relational persistence and query service for Java.
８、This is not the correct place because it leads to tightly coupled applications and code that can be hard to maintain over time.
９、“allow”的使用：This layer allows developers to stop building and maintaining unnecessary data transfer objects, or DTOs, to match their domain objects.
10,,This model allows Java developers to work with objects naturally in an OO fashion without additional coding.
11. allows for easier maintenance when troubleshooting
12.Inversion of control is a simple concept that allows objects to accept other objects that are created at a higher level.
13.Since Hibernate works with POJOs we will use our domain objects for persistence.
14.Here is the interface for the business service object that is stubbed for a DAO object dependency