public class UserDaoJdbcImpl implements UserDao { public void update(User u) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; try {  conn = JdbcUtils.getConnection();  String sql = "update user set name = ?, birthday = ?, money = ? where id=?";  ps = conn.prepareStatement(sql);  // 首先得到該記錄  User user = getUserById(u.getId());  // 判斷字段是否需要修改  if (u.getName() == null) {  u.setName(user.getName());  }  if (u.getBirthday() == null) {  u.setBirthday(user.getBirthday());  }  if (u.getMoney() == 0) {  u.setMoney(user.getMoney());  }  ps.setString(1, u.getName());  ps.setDate(2, new java.sql.Date(u.getBirthday().getTime()));  ps.setDouble(3, u.getMoney());  ps.setInt(4, u.getId());  int i = ps.executeUpdate();  System.out.println("成功向user表中更新" + i + "條記錄"); } catch (SQLException e) {  e.printStackTrace(); } finally {  JdbcUtils.free(rs, ps, conn); } } public User getUserById(int id) { Connection conn = null; PreparedStatement ps = null; ResultSet rs = null; User user = null; try {  conn = JdbcUtils.getConnection();  String sql = "select * from user where id = ?";  ps = conn.prepareStatement(sql);  ps.setInt(1, id);  rs = ps.executeQuery();  if (rs.next()) {  user = new User();  user.setId(rs.getInt("id"));  user.setName(rs.getString("name"));  user.setBirthday(rs.getDate("birthday"));  user.setMoney(rs.getDouble("money"));  } } catch (SQLException e) {  e.printStackTrace(); } finally {  JdbcUtils.free(rs, ps, conn); } return user; }}

public static void main(String[] args) { UserDao ud = new UserDaoJdbcImpl(); User user = new User(); user.setId(9); user.setName("老師");//只修改name和birthday屬性 Date d = null; try {  SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");  d = sdf.parse("1999-9-14"); } catch (ParseException e) {  e.printStackTrace(); } user.setBirthday(d); //user.setMoney(1234);不修改money屬性 ud.update(user);}