注册案例[session]

注册功能：保存用户信息到数据库
验证码功能：
展示验证码：展示验证码图片，并可以点击切换
校验验证码：验证码填写不正确，则注册失败

注册案例 -- 校验验证码
判断程序生成的验证码和用户输入的验证码是否一样，如果不一样，则阻止注册
验证码图片访问和提交注册表单是两次请求，所以要将程序生成的验证码存入Session中

验证码存入session

@Override
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
      // 生成验证码
      ServletOutputStream os = response.getOutputStream();
      String checkCode = CheckCodeUtil.outputVerifyImage(100, 50, os, 4);
 
      // 存入Session
      HttpSession session = request.getSession();
      session.setAttribute("checkCodeGen",checkCode);
 
  }

保存表单获取session

@Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       //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;
        }