Spring Boot 生成图片验证码

基本原理就是用Java画张指定大小的图片，在图片上随机摆上若干个数字或字母，数字或字母要有一定的倾斜和位移，要变一下字体和颜色，再画几条干扰线，然后就可以返回给客户端了。

创建文件 CaptchaUtil.java，代码如下：

// Write your package


import javax.imageio.ImageIO;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.util.Base64;
import java.util.Random;

public class CaptchaUtil {

    private static Random random = new Random();
    private int width = 165;
    private int height = 45;
    private int lineSize = 30;
    private int randomStrNum = 6;

    private String randomString = "0123456789abcdefghijklmnpqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWSYZ";
    private final String sessionKey = "CAPTCHA_CODE";

    private static Color getRandomColor(int fc, int bc) {

        fc = Math.min(fc, 255);
        bc = Math.min(bc, 255);

        int r = fc + random.nextInt(bc - fc - 16);
        int g = fc + random.nextInt(bc - fc - 14);
        int b = fc + random.nextInt(bc - fc - 12);

        return new Color(r, g, b);
    }
    
    private Font getFont() {
        return new Font("Times New Roman", Font.ROMAN_BASELINE, 40);
    }

    private void drawLine(Graphics g) {
        int x = random.nextInt(width);
        int y = random.nextInt(height);
        int xl = random.nextInt(20);
        int yl = random.nextInt(10);
        g.drawLine(x, y, x + xl, y + yl);

    }

    private String getRandomString(int num) {
        num = num > 0 ? num : randomString.length();
        return String.valueOf(randomString.charAt(random.nextInt(num)));
    }

    private String drawString(Graphics g, String randomStr, int i) {
        g.setFont(getFont());
        g.setColor(getRandomColor(108, 190));
        // System.out.println(random.nextInt(randomString.length()));
        String rand = getRandomString(random.nextInt(randomString.length()));
        randomStr += rand;
        g.translate(random.nextInt(3), random.nextInt(6));
        g.drawString(rand, 40 * i + 10, 25);
        return randomStr;
    }

    public boolean validateCode(HttpServletRequest request, String captcha) {
        HttpSession session = request.getSession();
        if (session == null || captcha == null) {
            return false;
        }
        if (session.getAttribute(sessionKey) == null) {
            return false;
        }
        return session.getAttribute(sessionKey).toString().toLowerCase().equals(captcha.toLowerCase());
    }

    public void clear(HttpServletRequest request) {
        HttpSession session = request.getSession();
        session.removeAttribute(sessionKey);
    }

    public void getRandomCodeImage(HttpServletRequest request, HttpServletResponse response) {
        HttpSession session = request.getSession();
        // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        Graphics g = image.getGraphics();
        g.fillRect(0, 0, width, height);
        g.setColor(getRandomColor(105, 189));
        g.setFont(getFont());
        // 干扰线
        for (int i = 0; i < lineSize; i++) {
            drawLine(g);
        }
        // 随机字符
        String randomStr = "";
        for (int i = 0; i < randomStrNum; i++) {
            randomStr = drawString(g, randomStr, i);
        }
        System.out.println("随机字符：" + randomStr);
        g.dispose();
        // 移除之前的session中的验证码信息
        session.removeAttribute(sessionKey);
        // 重新将验证码放入session
        session.setAttribute(sessionKey, randomStr);
        try {
            // 将图片以png格式返回,返回的是图片
            ImageIO.write(image, "PNG", response.getOutputStream());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    // 生成随机图片的base64编码字符串
    public String getRandomCodeBase64(HttpServletRequest request, HttpServletResponse response) {
        HttpSession session = request.getSession();
        // BufferedImage类是具有缓冲区的Image类,Image类是用于描述图像信息的类
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
        Graphics g = image.getGraphics();
        g.fillRect(0, 0, width, height);
        g.setColor(getRandomColor(105, 189));
        g.setFont(getFont());
        // 干扰线
        for (int i = 0; i < lineSize; i++) {
            drawLine(g);
        }

        // 随机字符
        String randomStr = "";
        for (int i = 0; i < randomStrNum; i++) {
            randomStr = drawString(g, randomStr, i);
        }
        System.out.println("随机字符：" + randomStr);
        g.dispose();
        session.removeAttribute(sessionKey);
        session.setAttribute(sessionKey, randomStr);
        String base64String = "";
        try {
            // 直接返回图片
            // ImageIO.write(image, "PNG", response.getOutputStream());
            // 返回 base64
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            ImageIO.write(image, "PNG", bos);

            byte[] bytes = bos.toByteArray();
            Base64.Encoder encoder = Base64.getEncoder();
            base64String = encoder.encodeToString(bytes);

        } catch (Exception e) {
            e.printStackTrace();
        }
        return base64String;
    }
}

可随机生成图片或Base64。在字母中去掉了o和I这两个容易引起误判的字母。

接下来就是 Controller，创建图片的 Controller：

    @GetMapping(value = "/api/captcha")
    @ApiOperation("获取验证码")
    public void getCaptchaImg(HttpServletRequest request, HttpServletResponse response, HttpSession session) {
        try {
            response.setContentType("image/png");
            response.setHeader("Cache-Control", "no-cache");
            response.setHeader("Expire", "0");
            response.setHeader("Pragma", "no-cache");
            ValidateCodeUtil validateCode = new ValidateCodeUtil();
            validateCode.getRandomCodeImage(request, response);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

在登录的 Controller 中进行验证：

ValidateCodeUtil validateCode = new ValidateCodeUtil();
if (!validateCode.validateCode(request, user.getCaptcha())) {
    throw new Exception("验证码错误");
} else {
    validateCode.clear(request);
}

验证成功后，clear 一下。