验证码实现步骤

package cn.kkforhai.web.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.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * @author KuKaFei.Hai
 * @date 2020/5/24 : 17:24
 */
@WebServlet("/VrificationCode")
public class VrificationCode extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.定义验证码的长，宽
        int width = 100;
        int height = 50;
        //2.创建一个对象，在内存中画图（验证码图像）
        BufferedImage vriImageCode = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //3.美化图片
        //3.1 获取画笔对象
        Graphics pen = vriImageCode.getGraphics();
        //3.2 用画笔颜色
        pen.setColor(Color.pink);
        //3.3 用画笔填充背景色
        pen.fillRect(0, 0, width, height);
        //3.4 重新设置画颜色，用来画边框
        pen.setColor(Color.blue);
        //3.5 画边框
        pen.drawRect(0, 0, width - 1, height - 1);
        //4 生成 4个随机的字符，并写入图片中
        //4.1 定义字符串
        String strCode = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        //4.2 生成随机坐标并取值
        Random ranNum = new Random();
        //4.3 循环4次
        for (int i = 1; i <= 4; i++) {
            //生成随机数角标
            int index = ranNum.nextInt(strCode.length());
            //获取字符
            char indexChar = strCode.charAt(index);
            //写入图片
            pen.drawString(String.valueOf(indexChar) + " ", width / 5 * i, height / 2);

        }
        //5 画干扰线
        //5.1设置画笔颜色
        pen.setColor(Color.green);
        for (int i = 0; i <= 4; i++) {
            //5.2 随机设置每条线起点，终点，坐标，
            int x1 = ranNum.nextInt(width);
            int y1 = ranNum.nextInt(height);
            int x2 = ranNum.nextInt(width);
            int y2 = ranNum.nextInt(height);
            //画线
            pen.drawLine(x1,y1,x2,y2);

        }
        //6.将图片输出到展示的页面
        ImageIO.write(vriImageCode, "jpg", resp.getOutputStream());
    }

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

页面引用：