Java write verification code

out.println("验证码<input  type='text' name='checkcode'/>

<img src='/Servlet4/CreateCode'/><br />");

src='/project name/ class name'
public class CreateCode extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1. Disable browser caching of random images       response.setDateHeader("Expires", - 1);       response.setHeader("Cache-Control", "no-cache");       response.setHeader("Pragma", "no-cache");     //2. Notify the client to open the sent data       response as a picture .setHeader("Content-Type", "image/jpep");       //1. Create a picture in memory       BufferedImage image=new BufferedImage(80,30,BufferedImage.TYPE_INT_BGR);       //2. Write data up       Graphics g=image.getGraphics();       //Set the background color       g.setColor(Color.BLACK);     



     
 

     





     


      g.fillRect(0,0,80,30);
     
      //3. Set the color and font of the written data
       g.setColor(Color.WHITE);
       g.setFont(new Font(null,Font.BOLD,20)) ;//???
     // 4. Write data to the picture
       String num=makeNum();
       //This sentence is a randomly generated value, which is saved to session
       request.getSession().setAttribute("checkcode", num );
       g.drawString(num, 0, 20);
      
      //3. Output the written data image to the browser
       ImageIO.write(image, "jpg",response.getOutputStream());
      
}   
   //4. The Randomly generate 7 digits when the function is used
    public String makeNum(){
  Random r=new Random();
  String num =r.nextInt(9999999)+"";
  StringBuffer sb=new StringBuffer();
  for(int i=0;i <7-num.length();i++){
  sb.append("0");
  }
  num=sb.toString()+num;
  return num;
}