try {
            server.start();
        } catch (final Exception e) {
            throw new CrawlerSystemException(e);
        }
    }

    public void stop() {
        try {
            server.stop();
            server.join();
        } catch (final Exception e) {
            throw new CrawlerSystemException(e);
        } finally {
            if (tempDocRoot) {
                docRoot.delete();
            }

        if (StringUtil.isBlank(regex)) {
            throw new CrawlerSystemException(
                    "URL pattern regular expression is null or blank. Cannot register client without a valid pattern.");
        }
        if (client == null) {
            throw new CrawlerSystemException("CrawlerClient instance is null. Cannot register null client.");
        }

        try {
            server.start();
        } catch (final Exception e) {
            throw new CrawlerSystemException(e);
        }
    }

    public void stop() {
        try {
            server.stop();
            server.join();
        } catch (final Exception e) {
            throw new CrawlerSystemException(e);
        } finally {
            if (tempDocRoot) {
                docRoot.delete();
            }

     *
     * @param uri the URI to preprocess
     * @return the preprocessed URI
     * @throws CrawlerSystemException if the URI is empty
     */
    protected String preprocessUri(final String uri) {
        if (StringUtil.isEmpty(uri)) {
            throw new CrawlerSystemException("File system URI is empty. Please provide a valid file path or file:// URI.");
        }

        String filePath = uri;

     * @return The list of compiled include patterns.
     * @throws CrawlerSystemException if the patterns cannot be loaded.
     */
    @Override
    public List<Pattern> getIncludeUrlPatternList(final String sessionId) {
        try {
            return includeFilterCache.get(sessionId);
        } catch (final ExecutionException e) {
            throw new CrawlerSystemException(e);
        }
    }

    /**

     * @param uri the URI to preprocess
     * @return the preprocessed URI with gcs:// prefix
     * @throws CrawlerSystemException if the URI is empty
     */
    protected String preprocessUri(final String uri) {
        if (StringUtil.isEmpty(uri)) {
            throw new CrawlerSystemException("GCS URI is empty. Please provide a valid GCS URI (gcs://...).");
        }

        String filePath = uri;

### Exception Hierarchy

All exceptions are unchecked (extend `RuntimeException` via `CrawlerSystemException`).

```
CrawlerSystemException (RuntimeException)
  ├─ CrawlingAccessException
  │     └─ MaxLengthExceededException
  ├─ ChildUrlsException
  ├─ ExtractException
  │     └─ UnsupportedExtractException

import org.codelibs.fess.crawler.client.http.config.WebAuthenticationConfig;
import org.codelibs.fess.crawler.client.http.config.WebAuthenticationConfig.AuthSchemeType;
import org.codelibs.fess.crawler.exception.CrawlerSystemException;
import org.codelibs.fess.opensearch.config.bsentity.BsWebAuthentication;
import org.codelibs.fess.opensearch.config.exentity.CrawlingConfig.ConfigName;

import org.codelibs.core.lang.StringUtil;
import org.codelibs.core.lang.ThreadUtil;
import org.codelibs.fess.crawler.Constants;
import org.codelibs.fess.crawler.exception.CrawlerSystemException;
import org.codelibs.fess.exception.CommandExecutionException;
import org.codelibs.fess.opensearch.user.exentity.User;

/**
 * Authentication chain implementation that executes external commands for user operations.

import org.codelibs.fess.crawler.entity.ResponseData;
import org.codelibs.fess.crawler.entity.ResultData;
import org.codelibs.fess.crawler.exception.ChildUrlsException;
import org.codelibs.fess.crawler.exception.CrawlerSystemException;
import org.codelibs.fess.crawler.exception.CrawlingAccessException;
import org.codelibs.fess.crawler.extractor.Extractor;
import org.codelibs.fess.crawler.extractor.impl.TikaExtractor;