1、添加kaptcha依赖

<!-- kaptcha验证码 -->
<dependency>
    <groupId>com.github.penggle</groupId>
    <artifactId>kaptcha</artifactId>
    <version>2.3.2</version>
</dependency>

2、新建KaptchaConfig配置类

package com.kuangstudy.config.code;

import com.google.code.kaptcha.impl.DefaultKaptcha;
import com.google.code.kaptcha.util.Config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Properties;

@Configuration
public class KaptchaConfig {
    @Bean
    public DefaultKaptcha getDefaultKaptcha(){
        DefaultKaptcha captchaProducer = new DefaultKaptcha();
        Properties properties = new Properties();
        properties.setProperty("kaptcha.border", "yes");
        properties.setProperty("kaptcha.border.color", "105,179,90");
        properties.setProperty("kaptcha.textproducer.font.color", "blue");
        properties.setProperty("kaptcha.image.width", "110");
        properties.setProperty("kaptcha.image.height", "40");
        properties.setProperty("kaptcha.textproducer.font.size", "30");
        properties.setProperty("kaptcha.session.key", "code");
        properties.setProperty("kaptcha.textproducer.char.length", "4");
        properties.setProperty("kaptcha.textproducer.font.names", "宋体,楷体,微软雅黑");
        Config config = new Config(properties);
        captchaProducer.setConfig(config);
        return captchaProducer;

    }
}

3、编写一个请求来生成验证码

package com.kuangstudy.controller.code;

import com.google.code.kaptcha.Constants;
import com.google.code.kaptcha.Producer;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.awt.image.BufferedImage;

@Controller
public class CodeController {
    @Autowired
    private Producer captchaProducer ;

    @RequestMapping("/kaptcha")
    public void getKaptchaImage(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpSession session = request.getSession();
        response.setDateHeader("Expires", 0);
        response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");
        response.addHeader("Cache-Control", "post-check=0, pre-check=0");
        response.setHeader("Pragma", "no-cache");
        response.setContentType("image/jpeg");
        //生成验证码
        String capText = captchaProducer.createText();
        session.setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);
        //向客户端写出
        BufferedImage bi = captchaProducer.createImage(capText);
        ServletOutputStream out = response.getOutputStream();
        ImageIO.write(bi, "jpg", out);
        try {
            out.flush();
        } finally {
            out.close();
        }
    }
}

4、页面显示

 <img src="/kaptcha" title="看不清，点击换一张！" onclick="this.src='/kaptcha?d='+new Date().getTime()" id="img">