一个简单的验证码小例子

jsp代码：

?生成验证码图片的servlet代码：
@WebServlet(urlPatterns="/login")public class Checknum extends HttpServlet{   @Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {    String checknum=(String) req.getSession().getAttribute("randnum");    String imageCode= req.getParameter("imageCode");    if(checknum.equals(imageCode)){    resp.sendRedirect(req.getContextPath()+"/index.jsp");    }else{    resp.sendRedirect(req.getContextPath()+"/checknum.jsp");    }    }}
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