[网络协议]BUG记录：HTTP Status 500 - Cannot forward after response has been committed

问题：

代码环境

原因：

1. 代码自动继承了父类的方法super.doPost(req, resp)

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);

        //1.获取请求的参数
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        String email = req.getParameter("email");
        String code = req.getParameter("code");
        //2.检查验证码是否正确=====写死，要求验证码为：abcde
        if("abcde".equalsIgnoreCase(code)){
            if (userService.existsUsername(username)) {
                System.out.println("用户名已存在");
                req.getRequestDispatcher("/pages/user/regist.html").forward(req, resp);

            }else{
                userService.registUser(new User(null,username,password,email));
                req.getRequestDispatcher("/pages/user/regist_success.html").forward(req, resp);
            }
        }else{
            System.out.println("验证码错误["+code+"]错误");
            req.getRequestDispatcher("/pages/user/regist.html").forward(req, resp);
        }
    }

解决方法：

1. 将super.doPost(req, resp)代码去掉