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copied!<p>I don't see the benefit of using the Command design pattern in this case. <br> 1. The idea with DAO, is to provide an interface that abstract a persistence mechanism. This interface traditionally defines CRUD methods. Each DAO concrete class, would typically implement the DAO interface, for a specific persistence mechanism.For instance, you could have one implementation that stores data into a relational database and another that stores data into an xml file. Both these implementation can be interchangeable since they implement the same inteface.<br> 2. The service functionality can be separated into a separate service layer. Normally, this layer has a dependency on your DAO layer(for persistence). The service interface can be similar to a façade that exposes the business logic implemented in the application (typically, logic in the business layer) to potential clients. Example:<br> <strong>User DAO interface:</strong></p> <pre> public interface UserDao { void save(User user); void delete(User user); void update(User user); User findByUsername(String username); List findAll(); ... } </pre> <p><strong>User Service interface:</strong><br></p> <pre> public interface UserService { void createUser(String username, String password); boolean loginUser(String username, String password); boolean isUsernameUnique(String username); .... } </pre> <p><strong>Service implementation:</strong><br></p> <pre> public class UserServiceImpl implements UserService { private UserDao userDao; public UserServiceImpl(UserDao userDao){ this.userDao = userDao; } ... } </pre>

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