简单的验证码

package org.example.servlet;

import com.sun.javafx.iio.ImageStorage;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class ImageServletDemo extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器5秒自动刷新一次
        resp.setHeader("refresh","3");
        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(120, 80, BufferedImage.TYPE_INT_RGB);
        //获得画笔对象
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
        //设置图片的背景颜色
        graphics.setColor(Color.black);
        graphics.fillRect(0,0,120,80);
        //给图片写数据
        graphics.setColor(Color.white);
        graphics.setFont(new Font("",Font.BOLD,20));
        for (int i = 0; i < 4; i++) {
            graphics.drawString(getRandomData(),20*i+20,50);
        }
        //告诉浏览器，这个请求以图片的形式打开
        resp.setContentType("image/jpeg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //把图片写给浏览器
        ImageIO.write(bufferedImage,"jpg",resp.getOutputStream());
    }

    private String getRandomData(){
        String data="1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        int rand=new Random().nextInt(data.length());
        return String.valueOf(data.charAt(rand));
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req,resp);
    }
}

验证码样式

ps: 可根据注释改变颜色和背景色