in my jpa project i needed DAOs… Data Access Objects… and the concept to implement those should be generic… initially this concept is confusing as hell… but after that its kinda cool 🙂
Each Entity needs an DAO and for every entity there are 6 object involved:
- interfcae GenericDao<T, K>: the main Interface with the basic DAO functions (CRUD(create, read, update, delete))
- class GenericDaoImpl<T, K>: implements the GenericDao interface.
- interface <entity>Dao: interface of the entity DAO, implements the GenericDao<<entityType>, <entityPrimaryKeyType>>
- class <entity>DaoImpl: implementation of the entity Dao. it is extended by the GenericDaoImpl
- class <entity>: the entity class
- class <entity>DaoTest: testing rocks 🙂
confused? ok heres the example: partly in pseudo code…
Basic things:
public interface GenericDao<T, K extends Serializable>{
T findById(K id, boolean lock);
List<T> findAll();
T save(T entity);
void delete(T entity);
}
public abstract class GenericDaoImpl<T, K extends Serializable> implements GenericDao<T, K>
public Person{
 int id;
 string name
}
Person Dao:
public interface PersionDao extends GenericDao<Persion, Integer>
public class PersonDaoImpl extends GenericDaoImpl<Person, Integer> implements PersionDao
And thats it… in the GenericDaoImpl are all the methods for all entites and in the PersonDaoImpl the persion stuff…