JSP实现验证码(2)

  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);

  response.setContentLength(buf.length);

  out.flush();

  out.close();

 }

 private int fun(char[] rands){

  int num1=Integer.parseInt(rands[0]+"")*10+Integer.parseInt(rands[1]+"");

  int num2=Integer.parseInt(rands[2]+"");

  int num=0;

  if(rands[2]=='+'){

   num=num1+num2;

  }else{

    num=num1-num2;

  }

  return num;

 }

 private void drawRands(Graphics g, char[] rands) {

  g.setColor(Color.black);

  g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));

  g.drawString(" "+rands[0],1,20);

  g.drawString(" "+rands[1],14,17);

  g.drawString(" "+rands[3],30,16);

  g.drawString(" "+rands[2],42,18);

  g.drawString(" "+rands[4],56,16);

 }

 private char[] generateCheckCode() {

  String chars="0123456789";

  String char1="+-";

  char[] rands=new char[5];

  rands[0]=chars.charAt((int) (Math.random()*2)+1);

  rands[1]=chars.charAt((int) (Math.random()*10));

  rands[2]=chars.charAt((int) (Math.random()*9)+1);

  rands[3]=char1.charAt((int) (Math.random()*2));

  rands[4]='=';

  return rands;

 }

 private void drawBackground(Graphics g) {