使用Session实现一个一次性的验证码登录功能

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>


 
  
  
  
  
    
  
  
  
  
 
 
  
    

      

        

          
用户名*
          

        
      
        

          
密码
          

        
                  
        

          
输入验证码
          

            
            
            看不清，换一张
            ${imgError }
          
        
        
        

          

        
      
    
    
  
 

public class CheckImgServlet extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    int width = 120;
    int height = 40;
    // 先生成一张纸
    BufferedImage bufi = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    // 画笔
    Graphics g = bufi.getGraphics();
    // 设置背景颜色
    // 修改画笔颜色
    g.setColor(Color.white);
    // 填充
    g.fillRect(0, 0, width, height);
    // 绘制边框
    // 设置边框颜色
    g.setColor(Color.red);
    // 画边框
    g.drawRect(0, 0, width - 1, height - 1);
    // 准备一些数据
    String data = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890abcdefghijklmnopqrstuvwxyz";
    // 生成随机对象
    Random r = new Random();
    String checkcode = "";
    // 生成4个随机的数字
    for (int i = 0; i < 4; i++) {
      // 生成随机颜色
      g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
      // 设置字体
      g.setFont(new Font("宋体", Font.ITALIC, 25));
      String c = data.charAt(r.nextInt(data.length())) + "";
      g.drawString(c, 10 + (20 * i), 30);
      checkcode += c;
    }
    // 将生成的验证码放到 session中
    request.getSession().setAttribute("session_checkcode", checkcode);
    // 画干扰线
    for (int i = 0; i < 8; i++) {
      // 设置随机颜色
      g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
      // 画线 两点确定一线
      g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
    }
    // 将图片输出到浏览器
    ImageIO.write(bufi, "jpg", response.getOutputStream());
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  }
}

public class RegistServlet extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  }
  public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // 校验验证码的有效性: 服务端生成的验证码 和 表单提交的验证码一致才算有效
    // 服务端生成的验证码 保存在 session容器中
    // 获得session中的验证码
    HttpSession session = request.getSession();
    String session_checkcode = (String) session.getAttribute("session_checkcode");
    // 使用完后，迅速清除session中验证码的属性
    session.removeAttribute("session_checkcode");
    // 获得表单提交的验证码
    String form_checkcode = request.getParameter("form_checkcode");
    // 判断什么是非法 如果非法，终止
    if (session_checkcode == null || !session_checkcode.equals(form_checkcode)) {
      // 说明验证码错误
      request.setAttribute("imgError", "验证码错误！");
      // 将request对象转发给 login.jsp
      request.getRequestDispatcher("/login.jsp").forward(request, response);
      // 结束当前方法
      return;
    }
    // 如果合法， 继续校验用户名和密码的有效
    String username = request.getParameter("username");
    String password = request.getParameter("password");
  }
}