Java后端技术生成随机验证码图片

import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CaptchaGenerator {
  private static final int WIDTH = 90;
  private static final int HEIGHT = 30;
  private static final int FONT_SIZE = 20;

  public static void generate(HttpServletRequest request, HttpServletResponse response) throws Exception {
    response.setContentType("image/png");
    BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
    Graphics2D graphics = (Graphics2D) image.getGraphics();
    graphics.setColor(Color.WHITE);
    graphics.fillRect(0, 0, WIDTH, HEIGHT);
    graphics.setFont(new Font("Arial", Font.BOLD, FONT_SIZE));
    Random random = new Random();
    StringBuilder captchaBuilder = new StringBuilder();
    for (int i = 0; i <; 4; i++) {
      char captchaChar = (char) (random.nextInt(26) + 'A');
      captchaBuilder.append(captchaChar);
      graphics.setColor(new Color(random.nextFloat(), random.nextFloat(), random.nextFloat()));
      graphics.drawString(String.valueOf(captchaChar), i * 20 + 10, HEIGHT - (HEIGHT - FONT_SIZE) / 2);
    }
    request.getSession().setAttribute("captcha", captchaBuilder.toString());
    ServletOutputStream outputStream = response.getOutputStream();
    ImageIO.write(image, "png", outputStream);
    outputStream.flush();
    outputStream.close();
  }
}