DAO interface.
package com.jxee.ejb;
import javax.ejb.Local;
import com.jxee.model.User;
/**
* although it's not required, it's good practice to define a DAO interface.
* annotation @Local marks this as an EJB local interface.
*/
@Local
public interface UserDAO {
public User findUserByName(String username);
}
DAO implemented as an EJB3.1 Stateless bean
package com.jxee.ejb;
import javax.ejb.Stateless;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
import org.apache.log4j.Logger;
import com.jxee.model.User;
/**
* annotation @Stateless marks a POJO as a stateless EJB and thus it
* would have all the services available, like transaction management etc.
*/
@Stateless
public class UserDAOImp implements UserDAO {
private static final Logger log = Logger.getLogger(UserDAOImp.class);
// inject the persistence unit to have access to database
@PersistenceContext(unitName="punit.projee6")
private EntityManager em;
// @EJB AnotherEJB toInjectOtherEJB;
/**
* method throws runtime exception like "NoResultException" and
* "NonUniqueResultException" etc, which you dont need to handle.
* but you might want to handle it, such as "NoResultException".
*/
public User findUserByName(String username) {
log.debug("finding user for name: " + username);
String sql = "select u from User u where u.username = :username";
Query query = em.createQuery(sql);
query.setParameter("username", username);
return (User)query.getSingleResult(); // may throw runtime exceptions
}
}
小姐一下(本文不得不承認,windows中文輸入很邪惡 :twisted: ):
1。 從EJB3.0開始,開發EJB已經非常友善了。不需要處理lifecycle,不需要進行讨厭的xml配置,利用annotation很容易。做個譬喻:都是洋芋,但ejb2是帶泥的洋芋,而ejb3則不帶泥了,洗巴的幹幹淨淨,多好。EJBs阿POJOs,測試起來也比較容易了吧。。。如果你測試上瘾的話, 哈哈。。。 :lol:
2。 DI 很友善,死腦筋(spring)還有什麼優勢?真是三十年河東,又三十年河西。
3。 JPA在ORM架子上又抽象了一下,提供标準的API,這多舒坦啊,别再折騰XML了!
下一篇 CRUD 一下: jee6 學習筆記 4 - CRUD