使用JDBC工具类查询封装成对象和集合

public class JDBCQueryDemo1 {
    public static void main(String[] args) throws SQLException {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入您要查询的用户的uid：");
        String uid = sc.nextLine();
        User user = queryOneUserById(uid);
        if (user!=null){
            System.out.println("您查询的用户存在："+user);
        }else {
            System.out.println("您查询的用户不存在~~");
        }
        System.out.println("--------");
        List<User> list = queryAllUsers();
        for (User u : list) {
            System.out.println(u);
        }
    }
    //根据uid查询uesr对象
    public static User queryOneUserById(String uid) throws SQLException {
        //1.获取Connection连接对象
        Connection con = JDBCUtil.getConnect();
        //2.获取执行sql语句的Statement对象
        Statement stmt = con.createStatement();
        //3.执行查询操作
        String sql = "select * from users where uid = ‘"+uid+"‘";
        ResultSet rs = stmt.executeQuery(sql);
        //判断查询结果是否有数据
        if (rs.next()){
            //获取数据
            String uid1 = rs.getString("uid");
            String uname = rs.getString("uname");
            String upass = rs.getString("upass");
            User user = new User(uid1,uname,upass);

            return user;
        }
        //释放资源
        JDBCUtil.release(con,stmt,rs);
        return null;
    }

    //查询所有uesr对象：把对象放在List集合中，返回List集合
    public static List<User> queryAllUsers() throws SQLException {
        Connection con = JDBCUtil.getConnect();

        Statement stmt = con.createStatement();

        String sql = "select * from users";
        ResultSet rs = stmt.executeQuery(sql);
        List<User> list = new ArrayList<>();
        while (rs.next()){
            String uid = rs.getString("uid");
            String uname = rs.getString("uname");
            String upass = rs.getString("upass");
            User users = new User(uid,uname,upass);
            list.add(users);
        }
        //释放资源
        JDBCUtil.release(con,stmt,rs);

        //返回List集合
        return list;
    }
}