利用java实现验证码生成并完成验证

public void showCheckCode(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {  // 调用业务逻辑  String checkCode = getCheckCode();  //将验证码字符放入session域对象中  req.getSession().setAttribute("checkCode", checkCode);  //图片宽  int width = 80;  //图片高  int height = 30;  //在内存中创建一个图片  BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);  //获取一个画笔  Graphics g = image.getGraphics();  //设置画笔颜色，用灰色做背景  g.setColor(Color.GRAY);  //向Image中填充灰色  g.fillRect(0,0,width,height);  Random r = new Random();  //设置3条干扰线  for (int i = 0; i < 3; i++) {    g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255)));    g.drawLine(r.nextInt(80), r.nextInt(30), r.nextInt(80), r.nextInt(80));  }  //设置验证码字符串的颜色  g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255)));  //设置字符的大小  g.setFont(new Font("黑体",Font.BOLD,24));  //在图片中写入验证码字符串  g.drawString(checkCode,15,20);  //将Image对象以PNG格式输出给所有的客户端  ImageIO.write(image,"PNG",resp.getOutputStream());}public static String getCheckCode(){  //验证码中的字符由数字和大小写字母组成  String code = "0123456789qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";  Random r = new Random();  StringBuffer sb = new StringBuffer();  for (int i = 0; i < 4; i++) {    sb.append(code.charAt(r.nextInt(code.length())));  }  return sb.toString();}