<!--kaptcha-->
<dependency>
   <groupId>com.baomidou</groupId>
   <artifactId>kaptcha-spring-boot-starter</artifactId>
   <version>1.1.0</version>
</dependency>

#驗證碼
kaptcha:
 content:
   #源字符
   source: wjl

package com.example.security.security;

import com.google.code.kaptcha.Producer;
import org.apache.commons.codec.binary.Base64;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.util.FastByteArrayOutputStream;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.imageio.ImageIO;
import javax.servlet.http.HttpSession;
import java.awt.image.BufferedImage;
import java.io.IOException;

@RestController
public class KaptchaController{
   @Autowired
   private Producer producer;
   @GetMapping("/verify-code.png")
   public String getVerifyCode(HttpSession session) throws IOException{
       //1.生成驗證碼
       String kaptcha=producer.createText();
       //驗證碼圖片
       BufferedImage bi=producer.createImage(kaptcha);
       //2.存入session
       session.setAttribute("kaptcha",kaptcha);
       //3.把驗證碼圖片轉換成base64然后返回,前端拿到后解碼然后渲染即可成圖片.
       FastByteArrayOutputStream fos=new FastByteArrayOutputStream();
       ImageIO.write(bi,"png",fos);
       return Base64.encodeBase64String(fos.toByteArray());
   }
}