SqlSession取不到內容，報空指針錯誤怎么解決啊？

public class DBAccess {

public SqlSession getSqlSession() throws IOException {

// 讀取配置文件

Reader reader = Resources

.getResourceAsReader("Configuration.xml");

// 構建一個SqlSessionFactory

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder()

.build(reader);

// 通過上面得到的對象開啟一次回話

SqlSession sqlSession = sqlSessionFactory.openSession();

return sqlSession;

}

}

Dao層代碼

public List<Message> queryMessageList(String command , String description) {

DBAccess dbAccess = new DBAccess();

SqlSession sqlSession = null ;

try {

sqlSession = dbAccess.getSqlSession();

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

} finally {

sqlSession.close();

}

return null ;

}

測試類

public static void main(String[] args) {

MessageDao mdDao = new MessageDao();

mdDao.queryMessageList("", "");

}

異常信息：

Exception in thread "main" java.lang.NullPointerException

at com.micro.dao.MessageDao.queryMessageList(MessageDao.java:26)

at com.test.test.main(test.java:8)

出現問題：

SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);

Factory并沒有build出對象。。。。，這個問題怎么解決啊