产生随机验证码

 
protected void processRequest(HttpServletRequest request,

   HttpServletResponse response) throws ServletException, IOException {

  response.setContentType("image/jpeg");

  response.setHeader("Pragma", "No-cache");

  response.setHeader("Cache-Control", "no-cache");

  response.setDateHeader("Expires", 0);

  HttpSession session = request.getSession();

  // 在内存中创建图象

  int width = 60, height = 18;

  BufferedImage image = new BufferedImage(width, height,

    BufferedImage.TYPE_INT_RGB);

  // 获取图形上下文

  Graphics g = image.getGraphics();

  //生成随机类

  Random random = new Random();

  // 设定背景色

  g.setColor(getRandColor(200, 250));

  g.fillRect(0, 0, width, height);

  //设定字体

  g.setFont(new Font("Times New Roman", Font.PLAIN, 18));

  //画边框

  //g.setColor(new Color());

  //g.drawRect(0,0,width-1,height-1);

  // 随机产生155条干扰线，使图象中的认证码不逸被其它程序探测到

  g.setColor(getRandColor(160, 200));

  for (int i = 0; i < 155; i++) {

   int x = random.nextInt(width);

   int y = random.nextInt(height);

   int xl = random.nextInt(12);

   int yl = random.nextInt(12);

   g.drawLine(x, y, x + xl, y + yl);

  }

  // 取随机产生的认证码(4位数字)

  String sRand = "";

  for (int i = 0; i < 4; i++) {

   String rand = String.valueOf(random.nextInt(10));

   if(rand.equals("4")){

    rand="8";

   }

   sRand += rand;

   // 将认证码显示到图象中

   g.setColor(new Color(20 + random.nextInt(110), 20 + random

     .nextInt(110), 20 + random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成

   g.drawString(rand, 13 * i + 6, 16);

  }

  // 将认证码存入SESSION

  Object obj = request.getSession(false).getAttribute(SESSION_CAPTCHA);

  if(obj!=null){

   request.getSession(false).removeAttribute(SESSION_CAPTCHA);

  }

  session.setAttribute(SESSION_CAPTCHA, sRand);

  // 图象生效

  g.dispose();

  ServletOutputStream responseOutputStream = response.getOutputStream();

  // 输出图象到页面

  ImageIO.write(image, "JPEG", responseOutputStream);

  //以下关闭输入流！

  responseOutputStream.flush();

  responseOutputStream.close();

 }

 Color getRandColor(int fc, int bc) {//给定范围获得随机颜色

  Random random = new Random();

  if (fc > 255)

   fc = 255;

  if (bc > 255)

   bc = 255;

  int r = fc + random.nextInt(bc - fc);

  int g = fc + random.nextInt(bc - fc);

  int b = fc + random.nextInt(bc - fc);

  return new Color(r, g, b);

 }