java验证码代码实现（servlet演示）

杨.某某

于 2020-09-03 19:38:25 发布

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分类专栏：后端文章标签： servlet 验证码

本文链接：https://blog.youkuaiyun.com/qq_37823003/article/details/108391585

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以前看见各大网站都有图形化的验证码（虽然现在已经很少大型网站都不使用了）的时候就超级非常的好奇这个验证码到底是怎么实现的，真的是超级的羡慕…今天学习了很多东西，然后自己也来试着写了一下，为此记录下来，说不定以后会用得到吧 ~

这里以最原生的servlet来演示：

package com.service;

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;

//servlet3.0及以上可以使用注解，
@WebServlet("/ValidateCodeServlet")
public class ValidateCodeServlet extends HttpServlet {

//这个地方其实数字1和字母l，还有数字0和字母0很多时候会混淆，可以去掉。
//字符数组用来生成验证码
    private char[] codeSequence = {'A', '1', 'B', 'C', '2', 'D', '3', 'E', '4', 'F', '5', 'G', '6', 'H', '7', 'I', '8', 'J',
            'K', '9', 'L', '1', 'M', '2', 'N', 'P', '3', 'Q', '4', 'R', 'S', 'T', 'U', 'V', 'W',
            'X', 'Y', 'Z'};

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        int width = 76;
        int height = 45;
        Random random = new Random();
        //设置response头信息
        //禁止缓存
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);

        //生成缓冲区image类
        BufferedImage image = new BufferedImage(width, height, 1);
        //产生image类的Graphics用于绘制操作
        Graphics g = image.getGraphics();
        //Graphics类的样式 背景颜色
        g.setColor(new Color(16, 48, 77));//颜色可以随便改
        g.setFont(new Font("Times New Roman", 0, 25));
        g.fillRect(0, 0, width, height);
        //绘制干扰线
        for (int i = 0; i < 20; i++) {
            g.setColor(this.getColor(130, 200));
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            int x1 = random.nextInt(12);
            int y1 = random.nextInt(12);
            g.drawLine(x, y, x + x1, y + y1);
        }

        //绘制字符
        String strCode = "";
        for (int i = 0; i < 4; i++) {
            String rand = String.valueOf(codeSequence[random.nextInt(codeSequence.length)]);
            strCode = strCode + rand;
//            g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
            //设置字体颜色
            g.setColor(new Color(255, 255, 255));
            g.drawString(rand, 13 * i + 8, 30);//这里是所处图片的位置
        }
        //将字符保存到session中用于前端的验证
        request.getSession().setAttribute("authCode", strCode.toLowerCase());
        g.dispose();

        ImageIO.write(image, "JPEG", response.getOutputStream());
        response.getOutputStream().flush();

    }

    public Color getColor(int fc, int bc) {
        Random random = new Random();
        if (fc > 255)
            fc = 255;
        if (bc > 255)
            bc = 255;
        int r = fc + random.nextInt(bc - fc);
        int g = fc + random.nextInt(bc - fc);
        int b = fc + random.nextInt(bc - fc);
        return new Color(r, g, b);
    }
}

servlet3.0以下代码需要在web.xml中加入下面的映射

<servlet>
        <servlet-name>ValidateCodeServlet</servlet-name>
        <servlet-class>com.service.ValidateCodeServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ValidateCodeServlet</servlet-name>
        <url-pattern>/ValidateCodeServlet</url-pattern>
    </servlet-mapping>

最后来写个网页来演示一下：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>验证码测试</title>
</head>
<body>
<img src="/firstWeb/ValidateCodeServlet" />
</body>
</html>