Generic DAO pattern in Hibernate

Question

While working on hibernate we are following generic Hibernate DAO pattern as mentioned in Hibernate Doc also.

So as per this we are currently maintaining two parallel hi

Answer 1

Umesh I will show you how we implement this functionality

The interface

public interface Repository {

    void add(INSTANCE_CLASS instance);
    void merge(INSTANCE_CLASS instance);
    void remove(PRIMARY_KEY_CLASS id);
    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id);
    INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, Class fetchingStrategy, Object... args);
    List findAll();
    List findAll(Class fetchingStrategy, Object... args);
    List findAll(int pageNumber, int pageSize);
    List findAll(int pageNumber, int pageSize, Class fetchingStrategy, Object... args);
    List findAllByCriteria(Criteria criteria);
    List findAllByCriteria(Criteria criteria, Class fetchingStrategy, Object... args);
    List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria);
    List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, Class fetchingStrategy, Object... args);

}

Because you usually will not need all of methods shown above, we create an abstract class with the purpose of being a dummy implementation

public abstract class AbstractRepository implements Repository {

    public void add(INSTANCE_CLASS instance) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public void merge(INSTANCE_CLASS instance) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public void remove(PRIMARY_KEY_CLASS id) {
        throw new UnsupportedOperationException("Not supported yet.");
    }


    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public INSTANCE_CLASS findById(PRIMARY_KEY_CLASS id, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll() {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(int pageNumber, int pageSize) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAll(int pageNumber, int pageSize, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(Criteria criteria, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

    public List findAllByCriteria(int pageNumber, int pageSize, Criteria criteria, Class fetchingStrategy, Object... args) {
        throw new UnsupportedOperationException("Not supported yet.");
    }

}

Now, for instance, if you want a repository which needs only add method, you can use

public class PersonRepository extends AbstractRepository {

    public void add(Person instance) {
        /**
          * person implmentatiuon goes here
          */    
    }

}

If other developer try to access other than add method, he or she will get UnsupportedOperationException

Criteria is just a marker interface.

public interface Criteria {}

The purpose of some methods define a parameter Class fetchingStrategy is to match externalized named queries. This way, I avoid hand-coded string which is error-prone. This approach is used by JSR-303 bean validation, for instance, to validate groups of properties. See here

public class Person {
    public static interface PERSON_WITH_ADDRESS {}
}

The externalize named query is shown as follows

So when i want to retrieve all of person with address, i call

PersonRepository respository ...

List personList = repository.findAll(PERSON_WITH_ADDRESS.class);

findAll can be written as

public class PersonRepository extends AbstractRepository {

    List findAll(Class fetchingStrategy, Object... args) {
        if(fetchingStrategy.isAssignableFrom(PERSON_WITH_ADDRESS.class)) {
            sessionFactory.getCurrentSession()
                          .getNamedQuery(fetchingStrategy.getSimpleName())
                          .list();
        }

        throw new UnsupportedOperationException("Not supported yet.");
    }

}