How to implement GenericDAO class on Hibernate

Question

I want UserDao class to extend GenericDAO where i'll have all CRUD methods. I have read article from IBM: http://www.ibm.com/developerworks/java/library/j-genericdao/index.html , but i could not implement it. Could someone show me example based on my custom UserDao class.

@Transactional(value="myTransactionManager")
public class UserDao {

    @Qualifier("mySessionFactory")
    public SessionFactoryImpl sessionFactory;

    public void setSessionFactory(SessionFactoryImpl sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    public List<UserEntity> getAll() {
        Query query = sessionFactory.getCurrentSession().createQuery(
                "from UserEntity ");
        List<UserEntity> userList = query.list();
        return userList;
    }

    public void updaet(UserEntity userEntity) {
        sessionFactory.getCurrentSession().update(userEntity);
    }

    public void delete(UserEntity userEntity) {
        sessionFactory.getCurrentSession().delete(userEntity);
    }

    public void save(UserEntity userEntity) {
        sessionFactory.getCurrentSession().save(userEntity);
    }

}

i tried to write class like this

public class GenericDao{

    @Qualifier("mySessionFactory")
    public SessionFactoryImpl sessionFactory;

    public void setSessionFactory(SessionFactoryImpl sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    public <T> List<T> getAll(Class<T> t) {
        Query query = sessionFactory.getCurrentSession().createQuery(
                "from " + t.getName());
        List<T> list = query.list();
        return list;
    }

    public <T> void save(T t) {
        sessionFactory.getCurrentSession().save(t);
    }

    public <T> void update(T t) {
        sessionFactory.getCurrentSession().update(t);
    }

    public <T> void delete(T t) {
        sessionFactory.getCurrentSession().delete(t);
    }
}

but when i try to pull data with UserDao like this:

public List<UserEntity> getAll() {
    List<UserEntity> list = UserDao.findAll();
}

Eclipse IDE for line List<UserEntity> list = UserDao.findAll(); give error : The method findAll() is underfined for type UserDao.

You need to pass the type to GenericDao, GenericDao<T> and extends it, obviously... — dambros
– dambros, Commented Apr 13, 2016 at 7:53
UserDaodoes not extend GenericDaoYou not add the generics to the class definition. GenericDao <T, PK extends Serializable> — Jens
– Jens, Commented Apr 13, 2016 at 7:55
UserDao does not extend GenericDao in description. But when i extend it gives error as described. — Ramil Huseynov
– Ramil Huseynov, Commented Apr 13, 2016 at 8:57
I was implemented as per your requirement : github.com/srinivas1918/spring4-and-hibernate4/blob/master/src/… — Nalla Srinivas
– Nalla Srinivas, Commented Apr 13, 2016 at 12:13

jpprade · Accepted Answer · 2016-04-13 09:15:56Z

1

this is my implementation :

GenericDao :

@Repository
public class GenericDao<T extends DbObject> {

    @Autowired
    private SessionFactory sessionFactory;

    private Class<T> getParameterizedClass() {
        return (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }

    public T findById(final Serializable id) {
        return (T) getCurrentSession().get(getParameterizedClass(), id.toString());
    }

    public void persist(final T object) {
        getCurrentSession().persist(object);
    }

    public void saveOrUpdate(final T object) {
        getCurrentSession().saveOrUpdate(object);
    }

    public void delete(final T object) {
        getCurrentSession().delete(object);
    }

    public T merge(final T object) {
        return (T) getCurrentSession().merge(object);
    }

}

UserDao :

public class UserDao extends GenericDao<User> {

}

Entity :

@Entity
@Table(name = "...")    
public class User extends DbObject {
}

answered Apr 13, 2016 at 9:15

jpprade

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1 Comment

Ramil Huseynov Over a year ago

what this method for: private Class<T> getParameterizedClass() { return (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0]; }

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