JPADao.java

// yleiskäyttönen

package wad.varasto.database;

import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import org.springframework.stereotype.Repository;
import wad.varasto.domain.Huone;

public abstract class JPADao<T> implements DAO<T> {

    @PersistenceContext
    EntityManager entityManager;

    private Class clazz;
    
    public JPADao(Class clazz) {
        this.clazz = clazz;
    }   
    
    @Override
    public void create(T instance) {
        entityManager.merge(instance);
    }

    @Override
    public T read(int id) {

        return (T)entityManager.find(clazz, id);
    }

    @Override
    public void delete(T instance) {
        entityManager.remove(instance);
    }

    @Override
    public T update(T instance) {
        return entityManager.merge(instance);
    }
    
    @Override
    public List<T> list() {
        String TABLE = clazz.getName().substring(clazz.getName().lastIndexOf(".")+1);
        Query q = entityManager.createQuery("SELECT t FROM "+TABLE+" t");
        return q.getResultList();
    }
       
}

DAO.java

// yleiskäyttönen

package wad.varasto.database;

import java.util.List;

public interface DAO<T> {
    public void create(T instance);
    public T read(int id);
    public void delete(T instance);
    public T update(T instance);
    public List<T> list();
}

HenkiloDao.java

// jokaiselle Entyty-luokalle tällänen

package wad.varasto.database;

import wad.varasto.domain.Henkilo;

public interface HenkiloDao extends DAO<Henkilo> {    
}

JPAHenkiloDao.java

// ja tällänen

package wad.varasto.database;

import org.springframework.stereotype.Repository;
import wad.varasto.domain.Henkilo;

@Repository
public class JPAHenkiloDao extends JPADao<Henkilo> implements HenkiloDao {

    public JPAHenkiloDao() {
        super(Henkilo.class);
    }
    
}