三层架构登录注册功能

public interface UserMapper {


    /**
     * 根据用户名和密码查询用户对象
     * @param username
     * @param password
     * @return
     */
    @Select("select * from tb_user where username = #{username} and password = #{password}")
    User select(@Param("username") String username,@Param("password")  String password);

    /**
     * 根据用户名查询用户对象
     * @param username
     * @return
     */
    @Select("select * from tb_user where username = #{username}")
    User selectByUsername(String username);

    /**
     * 添加用户
     * @param user
     */
    @Insert("insert into tb_user values(null,#{username},#{password})")
    void add(User user);
}
service层

public class UserService {
    SqlSessionFactory factory = SqlSessionFactoryUtils.getSqlSessionFactory();

    /**
     * 登录方法
     * @param username
     * @param password
     * @return
     */

    public User login(String username,String password){
        //2. 获取SqlSession
        SqlSession sqlSession = factory.openSession();
        //3. 获取UserMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        //4. 调用方法
        User user = mapper.select(username, password);

        //释放资源
        sqlSession.close();

        return  user;
    }



    /**
     * 注册方法
     * @return
     */

    public boolean register(User user){
        //2. 获取SqlSession
        SqlSession sqlSession = factory.openSession();
        //3. 获取UserMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //4. 判断用户名是否存在
        User u = mapper.selectByUsername(user.getUsername());

        if(u == null){
            // 用户名不存在，注册
            mapper.add(user);
            sqlSession.commit();
        }
        sqlSession.close();

        return u == null;

    }
省略一个自动生成验证码的类

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    private UserService service = new UserService();

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1. 获取用户名和密码
        String username = request.getParameter("username");
        String password = request.getParameter("password");

        //获取复选框数据
        String remember = request.getParameter("remember");

        //2. 调用service查询
        User user = service.login(username, password);

        //3. 判断
        if(user != null){
            //登录成功，跳转到查询所有的BrandServlet

            //判断用户是否勾选记住我
            if("1".equals(remember)){
                //勾选了，发送Cookie

                //1. 创建Cookie对象
                Cookie c_username = new Cookie("username",username);
                Cookie c_password = new Cookie("password",password);
                // 设置Cookie的存活时间
                c_username.setMaxAge( 60 * 60 * 24 * 7);
                c_password.setMaxAge( 60 * 60 * 24 * 7);
                //2. 发送
                response.addCookie(c_username);
                response.addCookie(c_password);
            }

            //将登陆成功后的user对象，存储到session
            HttpSession session = request.getSession();
            session.setAttribute("user",user);

            String contextPath = request.getContextPath();
            response.sendRedirect(contextPath+"/selectAllServlet");
        }else {
            // 登录失败,

            // 存储错误信息到request
            request.setAttribute("login_msg","用户名或密码错误");

            // 跳转到login.jsp
            request.getRequestDispatcher("/login.jsp").forward(request,response);

        }
    }
注册：

//1. 获取用户名和密码数据
String username = request.getParameter("username");
String password = request.getParameter("password");

User user = new User();
user.setUsername(username);
user.setPassword(password);

// 获取用户输入的验证码
String checkCode = request.getParameter("checkCode");

// 程序生成的验证码，从Session获取
HttpSession session = request.getSession();
String checkCodeGen = (String) session.getAttribute("checkCodeGen");

// 比对
if(!checkCodeGen.equalsIgnoreCase(checkCode)){

    request.setAttribute("register_msg","验证码错误");
    request.getRequestDispatcher("/register.jsp").forward(request,response);

    // 不允许注册
    return;
}
//2. 调用service 注册
boolean flag = service.register(user);
//3. 判断注册成功与否
if(flag){
    //注册功能，跳转登陆页面

    request.setAttribute("register_msg","注册成功，请登录");
    request.getRequestDispatcher("/login.jsp").forward(request,response);
}else {
    //注册失败，跳转到注册页面

    request.setAttribute("register_msg","用户名已存在");
    request.getRequestDispatcher("/register.jsp").forward(request,response);
}