JAVA代码制作验证码，可用于注册等功能页面

要导入servlet-api.jar包

创建验证码的Util工具类：

先创建图片并生成随机的验证码字母

设置图片的底色，并用setFont函数将验证码画在图片上，如果想让验证码难一点，可以添加for循环的代码给图片增加旋转角度

给验证码增加干扰线，提高安全性

设置边框

创建VerifyPic的servlet，通过Util类获取代码，并存入session中，然后输送去前端页面

前端页面验证码如下：

完整Util工具类代码如下：

package com.sport.util;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.HashMap;
import java.util.Map;

public class VerifyUtil {
    public static Map<String, Object> generateVerify(){
        //创建一张图片
        BufferedImage verifyPic = new BufferedImage(120,40,BufferedImage.TYPE_3BYTE_BGR);
        //通过图片获取画笔
        Graphics2D g = verifyPic.createGraphics();
        //准备一个字母+数字的字典
        String letters = "23456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
        //规定验证码的位数
        int verifyLength = 4;
        //生成随机验证码
        String verifyCode = "";
        //循环取值
        for(int i=0; i<verifyLength; i++) {
            verifyCode +=letters.charAt((int)(Math.random()*letters.length()));
        }
        //将图片的底板由黑变白
        g.setColor(Color.white);
        g.fillRect(0, 0, 120, 40);
        //将验证码画在图片之上
        g.setFont(new Font("微软雅黑",Font.BOLD, 24));
        for (int i = 0; i < verifyLength; i++) {
            //随机产生一个角度
            double theta = Math.random() * Math.PI / 4 * ((int)(Math.random()*2) == 0?1:-1);
            //产生偏转
            g.rotate(theta, 24+i*22, 20);
            //每画一个字幕之前都随机给一个颜色
            g.setColor(new Color((int)(Math.random()*256), (int)(Math.random()*256), (int)(Math.random()*256)));
            g.drawString(verifyCode.charAt(i)+"", 20+i*22 , 26);
            //回正
            g.rotate(-theta, 24+i*22, 20);
        }
        //加入干扰线
        for (int i = 0; i < 5; i++) {
            //给随机颜色
            g.setColor(new Color((int)(Math.random()*256), (int)(Math.random()*256), (int)(Math.random()*256)));
            //画线
            g.drawLine((int)(Math.random()*120), (int)(Math.random()*40),
                    (int)(Math.random()*120), (int)(Math.random()*40));
        }
        //设置边框颜色
        g.setColor(Color.black);
        //给验证码一个外边框
        g.drawRect(0, 0, 118, 38);

        //将验证码和图片一起存入map
        Map<String, Object> data = new HashMap<String, Object>();
        data.put("verifyCode", verifyCode);
        data.put("verifyPic", verifyPic);

        return data;
    }
}

完整VerifyPic的代码如下：

package com.sport.servlet;

import com.sport.util.VerifyUtil;

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 javax.servlet.http.HttpSession;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Map;

@WebServlet("/VerifyPic")
public class VerifyPic extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Map<String, Object> data = VerifyUtil.generateVerify();
        //获取验证码
        String verifyCode = (String) data.get("verifyCode");
        //将验证码存入session
        HttpSession session = request.getSession();
        session.setAttribute("verifyCode", verifyCode);
        //获取图片
        BufferedImage verifyPic = (BufferedImage) data.get("verifyPic");
        //输出图片给前端，使用工具类ImageIO
        ImageIO.write(verifyPic, "jpg", response.getOutputStream());

    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }
}