@WebServlet("/loginServlet")

public class LoginServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //设置request编码

        request.setCharacterEncoding("utf-8");

        //获取参数

        String username = request.getParameter("username");

        String password = request.getParameter("password");

        String checkcode = request.getParameter("checkcode");

        //判断验证码是否正确

        HttpSession session = request.getSession();

        //获取验证码的值

        String checkCode_session = (String) session.getAttribute("checkCode");

        //一获取完，就立马删除，以保证验证码的一次性

        session.removeAttribute("checkCode");

        if (checkCode_session!=null&&checkCode_session.equalsIgnoreCase(checkcode)){//忽略大小写比较

            //验证码正确

            //1.判断验证码和密码是否一致

            if ("zhangsan".equals(username)&&"123".equals(password)){//完善是需要调用userDao查询数据库的

                //登陆成功

                //1.存储用户信息

                session.setAttribute("user",username);

                //2.重定向success.jsp

                response.sendRedirect(request.getContextPath()+"/success.jsp");

            }else {

                //登陆失败

                //1.存储信息到request域中

                request.setAttribute("login_error","用户名或密码 不正确");

                //2.转发

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

            }

        }else {

            //验证码不正确

            //1.存储信息到request域中

            request.setAttribute("cc_error","验证码不正确");

            //2.转发

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

        }

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        this.doPost(request, response);

    }

}

@WebServlet("/checkCodeServlet")

public class CheckCodeServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        int width=100;

        int height=50;

        BufferedImage image=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

        Graphics g = image.getGraphics();

        g.setColor(Color.green);

        g.drawRect(0,0,width,height);

        g.setColor(Color.yellow);

        g.fillRect(0,0,width-1,height-1);

        String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

        Random random=new Random();

        g.setColor(Color.magenta);

        StringBuilder sb = new StringBuilder();

        for (int i=1;i<=4;i++){

            int index = random.nextInt(str.length());

            char ch=str.charAt(index);

            g.drawString(ch+"",i*width/5,height/2);

            sb.append(ch);

        }

        String checkCode_session = sb.toString();

        HttpSession session=request.getSession();

        session.setAttribute("checkCode",checkCode_session);

        System.out.println("验证码是   :  " + checkCode_session);

        //画干扰线

        g.setColor(Color.green);

        for (int i = 0; i < 16; i++) {

            int x1=random.nextInt(width);

            int x2=random.nextInt(width);

            int y1=random.nextInt(height);

            int y2=random.nextInt(height);

            g.drawLine(x1,y1,x2,y2);

        }

        ImageIO.write(image,"jpg",response.getOutputStream());

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        this.doPost(request, response);

    }

}