These are simple Java Bean classes used to transfer data between the logical front and backend tiers. They are used by the backend DAO classes to transfer data from the database to the front end. They are used in the front end Action classes to store the changes made by the user and they are used in ActionForms to provide data to JSPs.
A Transfer Object class is created for each entity in the application.
For example, for a "Customer" entity a CustomerTO
class is created. Every attribute on the associated entity is represented
by a field on the TransferObject.
Transfer Objects implement the Versionable
interface so that
concurrent updates to the associated data can be detected.