DAO工厂模式

首先在src下面新建一个配置文件daoconfig.properites

内容如下：userDaoClass=com.mengya.dao.impl.UserDaoJdbcImpl

DaoFactory类的内容如下：

public class DaoFactory {

       private static UserDao userDao = null;  //UserDao是UserDaoJdbcImpl的接口

       private static DaoFactory instance = new DaoFactory();

       private DaoFactory() {

              try {

                     Properties prop = new Properties();

                     InputStream inStream = DaoFactory.class.getClassLoader()

                                   .getResourceAsStream("daoconfig.properties");

                     prop.load(inStream);

                     String userDaoClass = prop.getProperty("userDaoClass");

                     Class clazz = Class.forName(userDaoClass);

                     userDao = (UserDao) clazz.newInstance();

              } catch (Throwable e) {

                     throw new ExceptionInInitializerError(e);

              }

       }

 

       public static DaoFactory getInstance() {

              return instance;

       }

 

       public UserDao getUserDao() {

              return userDao;

       }

}

 

说明：private static UserDao userDao = null;

与private static DaoFactory instance = new DaoFactory();位置不能换。

程序执行顺序是首先申明了一个空的userDao,执行new DaoFactory()的时候将userDao实例化了,如果它们的顺序换了则会出错,userDao是null的.

 

测试:

public class UserDaoTest {

    public static void main(String[] args) {

       UserDao userDao = DaoFactory.getInstance().getUserDao();

       User user = new User();

       user.setBirthday(new Date());

       user.setName("dao name2");

       user.setMoney(1000.0f);

       

       userDao.addUser(user);

        System.out.println(user.getId());

    }

}