HttpServletResponse验证码功能实现

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

            resp.setHeader("refresh","3");//浏览器3秒刷新一次
           BufferedImage image = new BufferedImage(100,40,BufferedImage.TYPE_INT_RGB);//创建一张图片
            Graphics2D g = (Graphics2D) image.getGraphics(); //获得一支笔
           g.setColor(Color.white);
           g.fillRect(0,0,100,40);
            resp.setContentType("image/jpg"); //告诉浏览器请求用图片格式响应
            g.setColor(Color.blue);
              g.setFont(new Font(null,Font.BOLD,20));
            g.drawString(makenum(),10,20);
            //不让浏览器缓存
              resp.setDateHeader("expires",-1);
               resp.setHeader("Cache- Control","no-Cache");
               resp.setHeader("Pragma","no-Cache");
               //写出图片
             ImageIO.write(image,"png",resp.getOutputStream());


  }
      //生成随机数
         private  String  makenum(){

           Random random = new Random();
          String a = random.nextInt(8888888) +"";
              StringBuffer sb = new StringBuffer();


              for (int i =0;i<7-a.length();i++){

                         sb.append("0");
              }
             a= sb.toString()+a;
              return a;
         }
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    doGet(req, resp);
  }
}