So implementieren Sie die Codefunktion für die Webseitenüberprüfung in Java

package cn.bdqn.servlet;
 
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.font.ImageGraphicAttribute;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
 
 
@WebServlet(name = "Servlet",urlPatterns = "/yanCode")
public class Servlet extends HttpServlet {
 public void doPost(javax.servlet.http.HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
  this.doGet(request,response);
 
 }
 
 public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
  String s="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  Random random = new Random();
  int width=500;
  int height=50;
  BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
  Graphics graphics = image.getGraphics();//相当于画笔
  //画背景
  graphics.setColor(Color.gray);
  graphics.fillRect(0,0,width,height);
  graphics.setColor(Color.black);
  for (int i = 0; i <4 ; i++) {
   int index = random.nextInt(s.length());
   String c = s.substring(index, index + 1);
   graphics.drawString(c,width/5*(i+1),15);
  }
 
  ImageIO.write(image,"jpg",response.getOutputStream());
 
 
 }
}