jee6 学习笔记 3 - an EJB3.1 DAO

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（本文不得不承认，ｗｉｎｄｏｗｓ中文输入很邪恶 ）：

１。　从ＥＪＢ３．０开始，开发ＥＪＢ已经非常方便了。不需要处理ｌｉｆｅｃｙｃｌｅ，不需要进行讨厌的ｘｍｌ配置，利用ａｎｎｏｔａｔｉｏｎ很容易。做个譬喻：都是土豆，但ｅｊｂ２是带泥的土豆，而ｅｊｂ３则不带泥了，洗巴的干干净净，多好。ＥＪＢｓ阿ＰＯＪＯｓ，测试起来也比较容易了吧。。。如果你测试上瘾的话，　哈哈。。。

２。　ＤＩ　很方便，死脑筋（ｓｐｒｉｎｇ）还有什么优势？真是三十年河东，又三十年河西。

３。　ＪＰＡ在ＯＲＭ架子上又抽象了一下，提供标准的ＡＰＩ，这多舒坦啊，别再折腾ＸＭＬ了！

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