@WebServlet("/loginServlet")
public class loginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        String username=request.getParameter("username");
        String password=request.getParameter("password");
        String checkcode=request.getParameter("checkcode");

        HttpSession session = request.getSession();
        String checkCode_session = (String)session.getAttribute("checkCode_session");
        session.removeAttribute("checkCode_session");
        if(checkCode_session!=null&&checkCode_session.equalsIgnoreCase(checkcode)){
                if("zhangsan".equals(username)){
                    session.setAttribute("user",username);
                    response.sendRedirect(request.getContextPath()+"/success.jsp");
                }else{
                    request.setAttribute("login_error","用户名或者密码错误");
                    request.getRequestDispatcher("/login.jsp").forward(request,response);
                }
        }else{
            request.setAttribute("cc_error","验证码错误");
            request.getRequestDispatcher("/login.jsp").forward(request,response);
        }



    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

@WebServlet("/loginServlet")
public class loginServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        String username=request.getParameter("username");
        String password=request.getParameter("password");
        String checkcode=request.getParameter("checkcode");

        HttpSession session = request.getSession();
        String checkCode_session = (String)session.getAttribute("checkCode_session");
        session.removeAttribute("checkCode_session");
        if(checkCode_session!=null&&checkCode_session.equalsIgnoreCase(checkcode)){
                if("zhangsan".equals(username)){
                    session.setAttribute("user",username);
                    response.sendRedirect(request.getContextPath()+"/success.jsp");
                }else{
                    request.setAttribute("login_error","用户名或者密码错误");
                    request.getRequestDispatcher("/login.jsp").forward(request,response);
                }
        }else{
            request.setAttribute("cc_error","验证码错误");
            request.getRequestDispatcher("/login.jsp").forward(request,response);
        }



    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}