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();
            }

     */
    protected ResponseData doGet(final String url) {
        throw new CrawlerSystemException("GET method is not supported.");
    }

    /**
     * Performs a HEAD request.
     * @param url The URL to request.
     * @return The ResponseData.
     */
    protected ResponseData doHead(final String url) {
        throw new CrawlerSystemException("HEAD method is not supported.");
    }

    /**

     * @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);
        }
    }

    /**

### Exception Hierarchy

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

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

package org.codelibs.fess.crawler.exception;

/**
 * This exception is thrown when an error occurs during OpenSearch access.
 *
 * @author shinsuke
 *
 */
public class OpenSearchAccessException extends CrawlerSystemException {

    private static final long serialVersionUID = 1L;

    /**
     * Creates a new instance of OpenSearchAccessException.
     *
     * @param message the detail message
     */

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;