====== Hibernate Generic Dao ======
  * https://community.jboss.org/wiki/GenericDataAccessObjects

===== Generic Dao Interface =====
<code java>
public interface GenericDAO<T, ID extends Serializable> {  
  
    T findById(ID id, boolean lock);  
  
    List<T> findAll();  
  
    List<T> findByExample(T exampleInstance);  
  
    T makePersistent(T entity);  
  
    void makeTransient(T entity);  
}
</code>

===== Generic Dao class =====
<code java>
public abstract class GenericHibernateDAO<T, ID extends Serializable>  
        implements GenericDAO<T, ID> {  
  
    private Class<T> persistentClass;  
    private Session session;  
  
    public GenericHibernateDAO() {  
        this.persistentClass = (Class<T>) ((ParameterizedType) getClass()  
                                .getGenericSuperclass()).getActualTypeArguments()[0];  
     }  
  
    @SuppressWarnings("unchecked")  
    public void setSession(Session s) {  
        this.session = s;  
    }  
  
    protected Session getSession() {  
        if (session == null)  
            throw new IllegalStateException("Session has not been set on DAO before usage");  
        return session;  
    }  
  
    public Class<T> getPersistentClass() {  
        return persistentClass;  
    }  
  
    @SuppressWarnings("unchecked")  
    public T findById(ID id, boolean lock) {  
        T entity;  
        if (lock)  
            entity = (T) getSession().load(getPersistentClass(), id, LockMode.UPGRADE);  
        else  
            entity = (T) getSession().load(getPersistentClass(), id);  
  
        return entity;  
    }  
  
    @SuppressWarnings("unchecked")  
    public List<T> findAll() {  
        return findByCriteria();  
    }  
  
    @SuppressWarnings("unchecked")  
    public List<T> findByExample(T exampleInstance, String[] excludeProperty) {  
        Criteria crit = getSession().createCriteria(getPersistentClass());  
        Example example =  Example.create(exampleInstance);  
        for (String exclude : excludeProperty) {  
            example.excludeProperty(exclude);  
        }  
        crit.add(example);  
        return crit.list();  
    }  
  
    @SuppressWarnings("unchecked")  
    public T makePersistent(T entity) {  
        getSession().saveOrUpdate(entity);  
        return entity;  
    }  
  
    public void makeTransient(T entity) {  
        getSession().delete(entity);  
    }  
  
    public void flush() {  
        getSession().flush();  
    }  
  
    public void clear() {  
        getSession().clear();  
    }  
  
    /** 
     * Use this inside subclasses as a convenience method. 
     */  
    @SuppressWarnings("unchecked")  
    protected List<T> findByCriteria(Criterion... criterion) {  
        Criteria crit = getSession().createCriteria(getPersistentClass());  
        for (Criterion c : criterion) {  
            crit.add(c);  
        }  
        return crit.list();  
   }  
  
}  
</code>