code: public User get(String loginname, String password) {
          Connection conn = null;
          User user = null;
          if (loginname == null || password == null) return null;
          String cryptpassword = MD5.encodeString(password,null);
          try {
              conn = ConnectionUtils.getConnection();
              user = userDAO.get(conn,loginname,cryptpassword);
          } catch(SQLException e) {
              logger.error(e.getMessage());
          } finally {
              DbUtils.closeQuietly(conn);
          }
          return user;
      }
docs: {@inheritDoc}
  <p>
  安全考虑，password 属性为 null。</p>