https://code.google.com/archive/p/kaptcha/wikis/SpringUsage.wiki

<dependency>
    <groupId>com.github.penggle</groupId>
    <artifactId>kaptcha</artifactId>
    <version>2.3.2</version>
</dependency>

import com.google.code.kaptcha.Constants;
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 {

    /**
     * 验证码生成器参数
     */
    @Bean
    public DefaultKaptcha captchaProducer() {
        DefaultKaptcha captchaProducer = new DefaultKaptcha();
        Properties properties = new Properties();
        properties.setProperty(Constants.KAPTCHA_IMAGE_WIDTH, "100");
        properties.setProperty(Constants.KAPTCHA_IMAGE_HEIGHT, "30");
        properties.setProperty(Constants.KAPTCHA_TEXTPRODUCER_FONT_SIZE, "22");
        properties.setProperty(Constants.KAPTCHA_TEXTPRODUCER_CHAR_LENGTH, "4");
        properties.setProperty(Constants.KAPTCHA_TEXTPRODUCER_CHAR_SPACE, "6");
        properties.setProperty(Constants.KAPTCHA_TEXTPRODUCER_FONT_COLOR, "black");
        properties.setProperty(Constants.KAPTCHA_BORDER_COLOR, "LIGHT_GRAY");
        properties.setProperty(Constants.KAPTCHA_BACKGROUND_CLR_FROM, "WHITE");
        properties.setProperty(Constants.KAPTCHA_NOISE_IMPL, "com.google.code.kaptcha.impl.NoNoise");
        properties.setProperty(Constants.KAPTCHA_OBSCURIFICATOR_IMPL, "com.google.code.kaptcha.impl.ShadowGimpy");
        properties.setProperty(Constants.KAPTCHA_TEXTPRODUCER_CHAR_STRING, "0123456789");
        properties.setProperty(Constants.KAPTCHA_SESSION_CONFIG_KEY, "checkCode");
        Config config = new Config(properties);
        captchaProducer.setConfig(config);
        return captchaProducer;
    }

}

https://code.google.com/archive/p/kaptcha/wikis/ConfigParameters.wiki

import com.google.code.kaptcha.Constants;
import com.google.code.kaptcha.Producer;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;

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

@Slf4j
@Controller
@RequestMapping("/kaptcha")
public class KaptchaController {

    @Autowired
    private Producer captchaProducer;

    @RequestMapping("/getCode")
    public ModelAndView getKaptchaImage(HttpServletRequest request, HttpServletResponse response) throws Exception {
        response.setDateHeader("Expires", 0);
        // Set standard HTTP/1.1 no-cache headers.
        response.setHeader("Cache-Control", "no-store, no-cache, must-revalidate");
        // Set IE extended HTTP/1.1 no-cache headers (use addHeader).
        response.addHeader("Cache-Control", "post-check=0, pre-check=0");
        // Set standard HTTP/1.0 no-cache header.
        response.setHeader("Pragma", "no-cache");
        response.setContentType("image/jpeg");
        // create the text for the image
        String capText = captchaProducer.createText();
        log.info("******************验证码是: " + capText + "******************");
        // store the text in the session
        request.getSession().setAttribute(Constants.KAPTCHA_SESSION_KEY, capText);
        // create the image with the text
        BufferedImage bi = captchaProducer.createImage(capText);
        ServletOutputStream out = response.getOutputStream();
        // write the data out
        ImageIO.write(bi, "jpg", out);
        try {
            out.flush();
        } finally {
            out.close();
        }
        return null;
    }
}

kaptcha.border                     	| Border around kaptcha. Legal values are yes or no.                     			| yes 
kaptcha.border.color                   | Color of the border. Legal values are r,g,b (and optional alpha) or white,black,blue.         | black 
kaptcha.border.thickness               | Thickness of the border around kaptcha. Legal values are > 0.                   	        | 1 
kaptcha.image.width                    | Width in pixels of the kaptcha image.                    				        | 200 
kaptcha.image.height                   | Height in pixels of the kaptcha image.                   				        | 50 
kaptcha.producer.impl                  | The image producer.                       						        | com.google.code.kaptcha.impl.DefaultKaptcha 
kaptcha.textproducer.impl              | The text producer.                    						        | com.google.code.kaptcha.text.impl.DefaultTextCreator 
kaptcha.textproducer.char.string       | The characters that will create the kaptcha.                  			        | abcde2345678gfynmnpwx 
kaptcha.textproducer.char.length       | The number of characters to display.                    				        | 5 
kaptcha.textproducer.font.names        | A list of comma separated font names.                  				        | Arial, Courier 
kaptcha.textproducer.font.size         | The size of the font to use.                    					        | 40px. 
kaptcha.textproducer.font.color        | The color to use for the font. Legal values are r,g,b.              			        | black 
kaptcha.textproducer.char.space        | The space between the characters                					        | 2 
kaptcha.noise.impl                     | The noise producer.                  							        | com.google.code.kaptcha.impl.DefaultNoise 
kaptcha.noise.color                    | The noise color. Legal values are r,g,b.          				                | black 
kaptcha.obscurificator.impl            | The obscurificator implementation.                  					        | com.google.code.kaptcha.impl.WaterRipple 
kaptcha.background.impl                | The background implementation.                    					        | com.google.code.kaptcha.impl.DefaultBackground 
kaptcha.background.clear.from          | Starting background color. Legal values are r,g,b.                    		        | light grey 
kaptcha.background.clear.to            | Ending background color. Legal values are r,g,b.                   			        | white 
kaptcha.word.impl                      | The word renderer implementation.                     					| com.google.code.kaptcha.text.impl.DefaultWordRenderer 
kaptcha.session.key                    | The value for the kaptcha is generated and is put into the HttpSession. 			| KAPTCHA_SESSION_KEY 
				  This is the key value for that item in the session.                     
kaptcha.session.date                   | The date the kaptcha is generated is put into the HttpSession. 				| KAPTCHA_SESSION_DATE
				  This is the key value for that item in the session.