//PrintWriter out = response.getWriter();

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

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

  response.setIntHeader("Expires",0);

  //背景

 

  BufferedImage bi = new BufferedImage(WIDTH, HEIGHT,BufferedImage.TYPE_INT_RGB);

  Graphics g = bi.getGraphics();

  drawBackground(g);

 

  //随机产生验证码

  char[] rands=generateCheckCode();

 

  //System.out.println(fun(rands));

 

  HttpSession session=request.getSession();

 

  session.setAttribute("num",fun(rands)+"");//验证码==12-9=3；写入sesion对象

 

  drawRands(g,rands);

 

  ByteArrayOutputStream bos=new ByteArrayOutputStream();

 

  ImageIO.write(bi, "JPEG", bos);

 

  byte[] buf=bos.toByteArray();//将bi对象里面内容转化成字符

 

  out.write(buf);