Java implements production verification code

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Java implements production verification code

package com.example.demo05_1;

import javax.imageio.ImageIO;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.annotation.*;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * @Auther：沈公子
 * @Date：2023/3/10 - 9:43
 * 后端实现验证码功能
 **/

@WebServlet(name = "CodeServlet", value = "/CodeServlet")
public class CodeServlet extends HttpServlet {
    
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
        // 如何让浏览器3秒自动刷新一次
        response.setHeader("refresh","3");
        // 在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(45, 20, BufferedImage.TYPE_INT_RGB);
        // 得到图片
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
        // 设置图片的背景颜色
        graphics.setColor(Color.WHITE);
        graphics.fillRect(0,0,45,20);
        // 给图片写数据
        graphics.setColor(Color.BLUE);
        graphics.setFont(new Font(null,Font.BOLD,20));
        graphics.drawString(makeNum(),0,20);
        // 告诉浏览器，这个请求用图片的方式打开
        response.setContentType("image/jpeg");
        // 网站存在缓存，不让浏览器缓存
        response.setDateHeader("expires", -1);
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        // 把图片写给浏览器
        ImageIO.write(bufferedImage,"jpg",response.getOutputStream());
    }

    // 生成随机数
    private String makeNum() {
    
    
        Random random = new Random();
        String num = random.nextInt(9999)+"";
        StringBuffer stringBuffer = new StringBuffer();
        for (int i = 0; i < 4-num.length(); i++) {
    
    
            stringBuffer.append("0");
        }
        num = stringBuffer.toString()+num;
        return num;
    }
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    

    }
}