Two classes with almost duplicate code inside

Question

At this moment, I have two classes: UserHibernateDao and TicketHibernateDao :

 import java.util.List; import org.springframework.orm.hibernate3.support.HibernateDaoSupport; import model.dao.Dao; import model.entity.User; public class UserDaoHibernate extends HibernateDaoSupport implements Dao<User> { public User get(long id) { return getHibernateTemplate().get(User.class, id); } public void save(User user) { getHibernateTemplate().save(user); } public void remove(long id) { getHibernateTemplate().delete( getHibernateTemplate().get(User.class, id)); } } 

and second:

 import java.util.List; import org.springframework.orm.hibernate3.support.HibernateDaoSupport; import model.dao.Dao; import model.entity.Ticket; public class TicketDaoHibernate extends HibernateDaoSupport implements Dao<Ticket> { public Ticket get(long id) { return getHibernateTemplate().get(Ticket.class, id); } public void save(Ticket ticket) { getHibernateTemplate().save(ticket); } public void remove(long id) { getHibernateTemplate().delete( getHibernateTemplate().get(Ticket.class, id)); } public void save(Ticket ticket) { getHibernateTemplate().saveOrUpdate(ticket); } } 

I see that both classes contain almost equal methods and method implementations.

I think this is not very good. What do you think? Or is this normal?

Answer 1

Something like this should work for you, it is usually called the "Generic DAO Pattern".

 public abstract class BaseDaoHibernate<T> extends HibernateDaoSupport implements Dao<T> { private final Class<T> entityType; protected BaseDaoHibernate(Class<T> entityType) { this.entityType = entityType; } public T get(long id) { return getHibernateTemplate().get(entityType, id); } public void save(T entity) { getHibernateTemplate().save(entity); } public void remove(long id) { getHibernateTemplate().delete(get(id)); } } 

and then:

 public class TicketDaoHibernate extends BaseDaoHibernate<Ticket> { public TicketDaoHibernate() { super(Ticket.class); } } 

and

 public class UserDaoHibernate extends BaseDaoHibernate<User> { public UserDaoHibernate() { super(User.class); } } 

Answer 2

Use Generics and read this document. Fine.

Answer 3

Add the following useful method to public abstract Dao<T> :

 public Class<E> getEntityClass() { if (entityClass == null) { Type type = getClass().getGenericSuperclass(); if (type instanceof ParameterizedType) { ParameterizedType paramType = (ParameterizedType) type; entityClass = (Class<E>) paramType.getActualTypeArguments()[0]; } else throw new IllegalArgumentException("Could not guess entity class"); } return entityClass; } 

Then your get and remove methods can be transferred to Dao<T> and rewritten as:

 public T get(long id) { return getHibernateTemplate().get(getEntityClass(), id); } public void remove(long id) { getHibernateTemplate().delete(get(id)); }