/** Configuration key for crawler clients used in parameter maps */
    protected static final String CRAWLER_CLIENTS = "crawlerClients";

    /** HTTP status code for Not Found */
    private static final int HTTP_STATUS_NOT_FOUND = 404;

    /** HTTP status code for OK */
    private static final int HTTP_STATUS_OK = 200;

    /**

└── 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 ThumbnailGenerationException("No CrawlerClient: " + configId + ", url: " + url);
            }
            String u = url;
            for (int i = 0; i < maxRedirectCount; i++) {

        final CrawlerClient client = mock(CrawlerClient.class);
        when(clientFactory.getClient("http://example.com/")).thenReturn(client);

        // Use reflection to access protected method
        final java.lang.reflect.Method method = CrawlerThread.class.getDeclaredMethod("getClient", String.class);
        method.setAccessible(true);

        assertEquals(5, testClient.count);
        assertEquals(url, response.getUrl());
        assertEquals(Constants.HEAD_METHOD, response.getMethod());
    }

    static class TestClient implements CrawlerClient {
        int count;

        int exceptionCount;

        long interval = 500;

        long previousTime;

        @Override

import org.codelibs.core.io.CloseableUtil;
import org.codelibs.core.lang.StringUtil;
import org.codelibs.core.lang.SystemUtil;
import org.codelibs.fess.crawler.builder.RequestDataBuilder;
import org.codelibs.fess.crawler.client.CrawlerClient;
import org.codelibs.fess.crawler.client.CrawlerClientFactory;
import org.codelibs.fess.crawler.container.CrawlerContainer;
import org.codelibs.fess.crawler.entity.AccessResult;

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;
            }

     */
    @Override
    public void close() {
        smbAuthenticationHolder = null;
    }

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

    /**