OA system -- save the verification code to session

package com.bjsxt.controller;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.sql.rowset.serial.SerialException;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;

@WebServlet("/codeServlet")
class CodeServlet extends HttpServlet{
    
   @override
   protected void service(HttpServletRequest req,HttpServletResponse resp)throws SerialException, IOException {
    
      // Create images in memory 
      int width = 110,height = 30;
      BufferedImage image = new BufferedImage(width,herght,BufferedImage,TYPE_INT_RGB);
      // Get the image context 
      Graphics g = image.getGraphics();
      // Set background color 
      g.setColor(getRandColor(fc:200,bc:250));
      g.fillRect(x:0,y:0,width,height);
      // set font 
      g.setFont(new Font(name:"Times New Roman", Font.PLAIN,size:20));
      // Randomly generated 155 Interference lines , Make the authentication code in the image difficult to be detected by other software 
      g.setColor(getRandColor(fc:160,bc:200));
      for(int i=0;i<155;i++){
    
         int x = randdom.nextInt(width);
         int y = randdom.nextInt(height);
         int x1 = randdom.nextInt(12);
         int y1 = randdom.nextInt(12);
         g.drawLine(x,y,x2:x+x1,y2:y+y1);
      }
      // Randomly generated authentication code （6 Digit number ）
      String sRand = "";
      for(int i = 0;i<6;i++){
    
         String rand = String.valueOf(randm.nextInt(10));
         sRand+=rand;
         // Display the authentication code in the image 
         g.setColor(new Color(20 + random.nextInt(100),20 + rand.nexInt(110),20 + rand.nextInt(110)));
         // Call the function out of the same color , Maybe because the seed table is close to , So we can only generate 
         g.drawString(rand,13 * i +6,16);
      }
      // Image generation 
      g.dispose();
      try{
    
         InmageIO.write(image,image,"JPEG",response.getOutputStream());
      }catch(Exception e){
    
         System.out.println(" Error in captcha image generation ："+e.toString());
      }
      // Save the verification code to Session
      request.getSession().setAttribute("randStr",sRand);
   }

}