How to Implement Secure and Stylish Captchas with Mica‑Captcha in Spring Boot

Captcha Effect

Ensures captcha security while maintaining aesthetics; feel free to try it, more usage examples are available in the mica demo project.

Dependency Coordinates

Maven

<dependency>
    <groupId>net.dreamlu</groupId>
    <artifactId>mica-captcha</artifactId>
</dependency>

Gradle

implementation "net.dreamlu:mica-captcha"

Configuration Items

Configuration Item

Default Value

Description

mica.captcha.cache-name

micaCaptchaCache

Name of the captcha cache (default: micaCaptchaCache)

mica.captcha.cookie-name

mica-captcha

Name of the captcha cookie (default: mica-captcha)

mica.captcha.enabled

true

Whether the captcha is enabled (default: true)

Note: When used with the mica-cache-redis component from mica‑pro, the cache name can be automatically configured with a timeout using the # placeholder.

Usage

First configure a Spring cache (e.g., EhCache, Redis) and set a timeout for micaCaptchaCache.

Servlet

Generate captcha

@Autowired
private MicaCaptchaServlet micaCaptcha;

/**
 * Image captcha endpoint
 */
@GetMapping(value = "/captcha.jpg", produces = MediaType.IMAGE_JPEG_VALUE)
@ResponseBody
public ResponseEntity<Resource> captcha(HttpServletResponse response) {
    return micaCaptcha.generate(response);
}

Validate captcha

boolean validated = micaCaptcha.validate(response, userInputCaptcha);

WebFlux

Generate captcha

@Autowired
private MicaCaptchaReactive micaCaptcha;

/**
 * Image captcha endpoint for WebFlux
 */
@GetMapping(value = "/captcha.jpg", produces = MediaType.IMAGE_JPEG_VALUE)
@ResponseBody
public Mono<ResponseEntity<Resource>> captcha(ServerWebExchange exchange) {
    return Mono.just(micaCaptcha.generate(exchange));
}

Validate captcha

boolean validated = micaCaptcha.validate(exchange, userInputCaptcha);

Generate Other Types of Captchas

micaCaptcha.generateBase64

– Generates a Base64‑encoded image captcha, suitable for mobile apps or front‑end/back‑end separation. micaCaptcha.validateBase64 – Validates a Base64‑encoded image captcha.