今日学习笔记

用户权限管理系统

完善用户登录功能，通过用户名查询到用户信息

 public User queryUserById(String userId) throws SQLException {
        String sql = "select u.* from userInfo u where u.userId=''"+userId+"''";
        User user = null;
        MySqlDB mySqlDB = new MySqlDB();
        Connection conn = mySqlDB.getConn();
        Statement stmt = null;
        ResultSet rs = null;
        try {
            stmt = conn.createStatement();
            rs = stmt.executeQuery(sql);
            while (rs.next()) {    
                 user = new User();
                user.setUserId(rs.getString("userId"));
                user.setUserName(rs.getString("userName"));
                user.setUserPassword(rs.getString("userPassword"));
                user.setRoleId(rs.getInt("roleId"));
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();

        }finally {
            assert rs != null;
            rs.close();
            stmt.close();
            conn.close();
        }
        return user;
    }
}

在userService中替换该声明

List<User> queryUsers() throws SQLException;

User queryUserById(String userId) throws SQLException;

Dao层的实现

@Override
public List<User> queryUsers() throws SQLException {
    UserDao userDao = new UserDaoimpl();
    return userDao.queryUsers();
}

@Override
public User queryUserById(String userId) throws SQLException {
    UserDao userDao = new UserDaoimpl();
    return userDao.queryUserById(userId);
}
注意：每个项目功能都要有一个service方法，每个方法都要写一个实现过程，这是必不可少的，service中存放的是业务逻辑代码，dao中存放的是数据库相关控制，分别编写、存放，便于以后的更改。
调用Service

try {
    UserService userService = new UserServiceImpl();
    User user = userService.queryUserById(username);
    if ("admin".equals(username) && "123456".equals(password)) {
        req.setAttribute("username", username);
        req.getRequestDispatcher("/userServlet").forward(req, resp);
    } else {
        req.setAttribute("username", username);
        req.setAttribute("error","用户名或密码错误");
        req.getRequestDispatcher("/login.jsp").forward(req, resp);
            resp.sendRedirect("/longin.jsp");
    }
} catch (SQLException throwables) {
    throwables.printStackTrace();
}
判断：

user != null && user.getUserPassword().equals(password)
如果用户名正确，跳转用户密码，如果错误，则显示用户名不存在