请求转发和重定向实现与Ajax实现表单登陆

private void login(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String verifycode = request.getParameter("verifycode");
        String machinecode = (String) request.getSession().getAttribute("rand");

        if (verifycode.equalsIgnoreCase(machinecode)) {
            // 2.验证用户名和密码
            String username = request.getParameter("username");
            String password = request.getParameter("password");
            System.out.println(username);
            User user = userService.login(username, password);
            if (user != null) {
                // 登录成功
                request.getSession().setAttribute("user", user);
                response.sendRedirect("index.jsp");
            } else {
                // 登录失败
                request.setAttribute("msg", "用户名或密码错误");
                request.getRequestDispatcher("login.jsp").forward(request,
                        response);
            }

        } else {
            request.setAttribute("msg", "验证码错误");
            request.getRequestDispatcher("login.jsp")
                    .forward(request, response);
        }
    }
    
    private void login2(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String verifycode = request.getParameter("verifycode");
        String machinecode = (String) request.getSession().getAttribute("rand");

        if (verifycode.equalsIgnoreCase(machinecode)) {
            // 2.验证用户名和密码
            String username = request.getParameter("username");
            String password = request.getParameter("password");
            System.out.println(username);
            User user = userService.login(username, password);
            if (user != null) {
                // 登录成功
                request.getSession().setAttribute("user", user);
                PrintWriter out = response.getWriter();
                out.write(JSON.toJSONString(new MsgVo(1,"登陆成功")));
            } else {
                // 登录失败
                PrintWriter out = response.getWriter();
                out.write(JSON.toJSONString(new MsgVo(2,"用户名和密码错误")));
            }

        } else {
            PrintWriter out = response.getWriter();
            out.write(JSON.toJSONString(new MsgVo(3,"验证码错误")));
        }
    }