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 */

        final CrawlerClientFactory crawlerClientFactory = crawlingConfig.initializeClientFactory(ComponentUtil::getCrawlerClientFactory);
        final CrawlerClient client = crawlerClientFactory.getClient(url);
        if (client == null) {
            throw new CrawlingAccessException(
                    "CrawlerClient is null for URL: " + url + ". Unable to access the document without a crawler client.");
        }

                return;
            }

            final String url = dataMap.get(fessConfig.getIndexFieldUrl()).toString();
            final CrawlerClient client = crawlerClientFactory.getClient(url);
            if (client == null) {
                logger.warn("CrawlerClient not available for url='{}'. Protocol may not be supported.", url);
                return;
            }

└── 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);
    }

    /**

     */
    public void setCharset(final String charset) {
        this.charset = charset;
    }

    /*
     * (non-Javadoc)
     *
     * @see org.codelibs.fess.crawler.client.CrawlerClient#doGet(java.lang.String)
     */
    @Override
    public ResponseData doGet(final String uri) {
        return processRequest(uri, true);
    }

    /**
     * Executes a HEAD request for the given URL.