src/main/java
└── com
    └── icoderoad
        └── common
            └── util
                └── CaptchaCodeUtil.java

package com.icoderoad.common.util;

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.util.Random;

public class CaptchaCodeUtil {
    
    public static final String SESSION_KEY = "CAPTCHA_CODE";
    
    private final Random random = new Random();
    private final String codeSource = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    
    private int width = 80;
    private int height = 26;
    private int codeLength = 4;
    private int lineCount = 40;
    
    private Font getFont() {
        return new Font("Fixedsys", Font.PLAIN, 18);
    }
    
    private Color randomColor(int min, int max) {
        min = Math.min(min, 255);
        max = Math.min(max, 255);
        int r = min + random.nextInt(max - min);
        int g = min + random.nextInt(max - min);
        int b = min + random.nextInt(max - min);
        return new Color(r, g, b);
    }
    
    private void drawLine(Graphics g) {
        int x = random.nextInt(width);
        int y = random.nextInt(height);
        int xl = random.nextInt(12);
        int yl = random.nextInt(12);
        g.drawLine(x, y, x + xl, y + yl);
    }
    
    private String drawChar(Graphics g, int index) {
        g.setFont(getFont());
        g.setColor(randomColor(50, 160));
        String ch = String.valueOf(codeSource.charAt(random.nextInt(codeSource.length())));
        g.drawString(ch, 15 * index, 18);
        return ch;
    }
    
    public void generate(HttpServletRequest request, HttpServletResponse response) {
        HttpSession session = request.getSession();
        
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        
        for (int i = 0; i < lineCount; i++) {
            g.setColor(randomColor(120, 200));
            drawLine(g);
        }
        
        StringBuilder code = new StringBuilder();
        for (int i = 1; i <= codeLength; i++) {
            code.append(drawChar(g, i));
        }
        
        session.setAttribute(SESSION_KEY, code.toString());
        g.dispose();
        
        try {
            ImageIO.write(image, "JPEG", response.getOutputStream());
        } catch (Exception e) {
            throw new RuntimeException("生成驗(yàn)證碼失敗", e);
        }
    }
}

package com.icoderoad.web.controller;

import com.icoderoad.common.util.CaptchaCodeUtil;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@RestController
public class CaptchaController {
    
    @GetMapping("/captcha/custom")
    public void customCaptcha(HttpServletRequest request, HttpServletResponse response) {
        response.setContentType("image/jpeg");
        response.setHeader("Cache-Control", "no-cache");
        response.setHeader("Pragma", "no-cache");
        response.setDateHeader("Expires", 0);
        
        new CaptchaCodeUtil().generate(request, response);
    }
}

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-captcha</artifactId>
    <version>5.8.6</version>
</dependency>

@GetMapping("/captcha/line")
public void line(HttpServletResponse response) throws IOException {
    LineCaptcha captcha = CaptchaUtil.createLineCaptcha(130, 38, 5, 5);
    response.setContentType("image/jpeg");
    response.setHeader("Cache-Control", "no-cache");
    captcha.write(response.getOutputStream());
}

@GetMapping("/captcha/circle")
public void circle(HttpServletResponse response) throws IOException {
    CircleCaptcha captcha = CaptchaUtil.createCircleCaptcha(130, 38, 5, 20);
    response.setContentType("image/jpeg");
    response.setHeader("Cache-Control", "no-cache");
    captcha.write(response.getOutputStream());
}

@GetMapping("/captcha/shear")
public void shear(HttpServletResponse response) throws IOException {
    ShearCaptcha captcha = CaptchaUtil.createShearCaptcha(130, 38, 5, 5);
    response.setContentType("image/jpeg");
    response.setHeader("Cache-Control", "no-cache");
    captcha.write(response.getOutputStream());
}

@GetMapping("/captcha/gif")
public void gif(HttpServletResponse response) throws IOException {
    GifCaptcha captcha = CaptchaUtil.createGifCaptcha(130, 38, 5);
    response.setContentType("image/jpeg");
    response.setHeader("Cache-Control", "no-cache");
    captcha.write(response.getOutputStream());
}

@GetMapping("/captcha/number")
public void number(HttpServletResponse response) throws IOException {
    RandomGenerator generator = new RandomGenerator("0123456789", 4);
    LineCaptcha captcha = CaptchaUtil.createLineCaptcha(200, 80);
    captcha.setGenerator(generator);
    captcha.createCode();
    captcha.write(response.getOutputStream());
}

@GetMapping("/captcha/math")
public void math(HttpServletResponse response, HttpSession session) throws IOException {
    ShearCaptcha captcha = CaptchaUtil.createShearCaptcha(200, 45, 4, 4);
    captcha.setGenerator(new MathGenerator());
    captcha.createCode();
    session.setAttribute("MATH_CODE", captcha.getCode());
    captcha.write(response.getOutputStream());
}