POM依赖

        <dependency>
            <groupId>com.github.whvcse</groupId>
            <artifactId>easy-captcha</artifactId>
            <version>1.6.2</version>
        </dependency>

DEMO

import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@RestController
public class EasyCaptchaController {

    @RequestMapping("/png")
    public void png(HttpServletResponse response) throws IOException {
        // png类型
        SpecCaptcha captcha = new SpecCaptcha(130, 48);
        String text = captcha.text();// 获取验证码的字符
        char[] chars = captcha.textChar();// 获取验证码的字符数组

        System.out.println("验证码：" + text);
        System.out.println(chars);
        // 输出验证码
        captcha.out(response.getOutputStream());
    }

    @RequestMapping("/gif")
    public void gif(HttpServletResponse response) throws IOException {

        // 三个参数分别为宽、高、位数
        GifCaptcha gifCaptcha = new GifCaptcha(100, 48, 4);
        // 设置类型：字母数字混合
        gifCaptcha.setCharType(Captcha.TYPE_DEFAULT);
        //获取验证码
        String text = gifCaptcha.text();
        System.out.println("验证码为：" + text);
        // 输出验证码
        gifCaptcha.out(response.getOutputStream());
    }

    @RequestMapping("/zh")
    public void zh(HttpServletResponse response) throws IOException {

        // 中文类型
        ChineseCaptcha captcha = new ChineseCaptcha(130, 48);
        //获取验证码
        String text = captcha.text();
        System.out.println("验证码为：" + text);
        // 输出验证码
        captcha.out(response.getOutputStream());
    }

    @RequestMapping("/arithmetic")
    public void arithmetic(HttpServletResponse response) throws IOException {
        // 算术类型
        ArithmeticCaptcha captcha = new ArithmeticCaptcha(130, 48);
        captcha.setLen(3);  // 几位数运算，默认是两位
        captcha.getArithmeticString();  // 获取运算的公式：4-9+1=?
        String text = captcha.text();// 获取运算的结果：-4

        System.out.println("计算结果为："+text);
        // 输出验证码
        captcha.out(response.getOutputStream());
    }

}