* @param client The CrawlerClient instance.
     */
    @Override
    public void addClient(final String regex, final CrawlerClient client) {
        factory.addClient(regex, client);
    }

    /**
     * Adds a client to the wrapped factory at a specific position.
     * @param regex The regular expression for the client.
     * @param client The CrawlerClient instance.

     */
    public CrawlerClient getClient(final String urlKey) {
        if (StringUtil.isBlank(urlKey)) {
            return null;
        }

        for (final Map.Entry<Pattern, CrawlerClient> entry : clientMap.entrySet()) {
            final Matcher matcher = entry.getKey().matcher(urlKey);
            if (matcher.matches()) {
                return entry.getValue();
            }

    }

    /**
     * Closes the underlying CrawlerClient and releases any resources associated with it.
     *
     * @throws Exception if an error occurs during the close operation
     */
    @Override
    public void close() throws Exception {
        client.close();
    }

    /**
     * Returns the underlying CrawlerClient.
     * @return The CrawlerClient instance.
     */

    /** Value for HC5 client selection. */
    public static final String HC5_CLIENT = "hc5";

    /** The HC4 HTTP client instance. */
    protected CrawlerClient hc4Client;

    /** The HC5 HTTP client instance. */
    protected CrawlerClient hc5Client;

    /** Flag indicating which client is selected (true = hc5, false = hc4). */
    private boolean useHc5 = true;

    /**

                    config.initializeClientFactory(() -> ComponentUtil.getComponent(CrawlerClientFactory.class));
            final CrawlerClient client = crawlerClientFactory.getClient(url);
            if (client == null) {
                throw new ThumbnailGenerationException("No CrawlerClient: " + configId + ", url: " + url);
            }
            String u = url;
            for (int i = 0; i < maxRedirectCount; i++) {

import jakarta.annotation.Resource;

/**
 * Abstract base class for CrawlerClient implementations.
 * Provides common functionality for handling initialization parameters,
 * content length checks, and default method implementations.
 * It defines the basic structure and configuration options for crawler clients.
 */
public abstract class AbstractCrawlerClient implements CrawlerClient {

        if (logger.isDebugEnabled()) {
            logger.debug("loading {}", componentName);
        }
        try (CrawlerClient client = crawlerContainer.getComponent(componentName)) {
            crawlerClientFactory.addClient(regex, client);
        } catch (final Exception e) {
            if (logger.isDebugEnabled()) {

import org.codelibs.fess.crawler.helper.ContentLengthHelper;
import org.codelibs.fess.crawler.helper.MimeTypeHelper;

import jakarta.annotation.Resource;

/**
 * FileSystemClient is CrawlerClient implementation to crawl files on a file
 * system.
 *
 * @author shinsuke
 *
 */
public class FileSystemClient extends AbstractCrawlerClient {

    /** Logger instance for this class */

└── fess-crawler-opensearch/   # OpenSearch backend
```

### Key Design Patterns

- **Factory**: `CrawlerClientFactory`, `ExtractorFactory` - protocol/format-specific component selection
- **Strategy**: `CrawlerClient`, `Extractor`, `Transformer` - pluggable implementations
- **Builder**: `RequestDataBuilder`, `ExtractorBuilder` - fluent construction
- **Template Method**: `AbstractCrawlerClient`, `AbstractExtractor` - common logic with overrides

                config.initializeClientFactory(() -> ComponentUtil.getComponent(CrawlerClientFactory.class));
        final CrawlerClient client = crawlerClientFactory.getClient(url);
        if (client == null) {
            throw new FessSystemException("No CrawlerClient: " + configId + ", url: " + url);
        }
        return writeContent(configId, url, client);
    }

    /**