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<h1>Image CAPTCHA</h1>
<p>Image CAPTCHA helps prevent malicious activities such as bot registration and spamming. It is generally recommended to add this protection when performing write operations on public-facing interfaces.</p>
<h2>Usage</h2>
<h3>YAML Configuration</h3>
<pre><code class="language-yaml">security:
ImageCaptcha: # Image CAPTCHA
enabled: true
expireSeconds: 60
</code></pre>
<h2>Configuration</h2>
<p>Create a configuration class and add it to the Spring container. The main purpose is to determine which image generator and caching method to use. For simplicity, we use the JVM's built-in <code>SimpleCache</code> here.<br>
If you want to switch to Redis, you can configure <code>SaveToRam</code>, <code>CaptchaCodeFromRam</code>, and <code>RemoveByKey</code> as shown below.</p>
<pre><code class="language-java">static final SimpleCache RAM = new SimpleCache(); // JVM cache
@Bean
ImageCaptchaConfig ImageCaptchaConfig() {
ImageCaptchaConfig config = new ImageCaptchaConfig();
config.setCaptchaImageProvider(new SimpleCaptchaImage());
config.setSaveToRam(RAM::add);
config.setCaptchaCodeFromRam(key -> {
SimpleCache.Item item = RAM.get(key);
return item == null ? null : item.getValue();
});
config.setRemoveByKey(RAM::remove);
return config;
}
</code></pre>
<h3>Add a Controller</h3>
<p>Add an API endpoint that returns the image CAPTCHA:</p>
<pre><code class="language-java">@Autowired
ImageCaptcha imageCaptcha;
@GetMapping("/captcha")
void showCaptcha(HttpServletRequest req, HttpServletResponse response) {
imageCaptcha.captchaImage(req, response);
}
</code></pre>
<p>The frontend must include a <code>uuid</code> parameter when requesting this endpoint, which serves as the unique identifier for this CAPTCHA generation. It's recommended to pass it via query string, for example: <code>/captcha?uuid=xxx</code>.</p>
<h3>Protect an API</h3>
<p>Add the <code>@ImageCaptchaCheck</code> annotation to the API you want to protect:</p>
<pre><code class="language-java">@PostMapping("/create_user")
@ImageCaptchaCheck
boolean createUser(@ModelAttribute User user);
</code></pre>
<p>That's basically all you need. The interceptor will automatically verify the CAPTCHA. If valid, the request proceeds to the business logic; otherwise, an exception is thrown and intercepted.</p>
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