}
        };
        CrawlingParameterUtil.setDataService(service);
        assertNotNull(CrawlingParameterUtil.getDataService());

        // Set to null
        CrawlingParameterUtil.setDataService(null);

        // Should be null now
        assertNull(CrawlingParameterUtil.getDataService());
    }

 * CrawlingParameterUtil.setUrlQueueService(newUrlQueueService);
 *
 * DataService<AccessResult<?>> dataService = CrawlingParameterUtil.getDataService();
 * CrawlingParameterUtil.setDataService(newDataService);
 * }
 * </pre>
 *
 * <p>Note: If a parameter is set to {@code null}, the corresponding ThreadLocal variable is removed.</p>
 */
public final class CrawlingParameterUtil {

        // set urlQueue to thread
        CrawlingParameterUtil.setCrawlerContext(crawlerContext);
        CrawlingParameterUtil.setUrlQueueService(urlQueueService);
        CrawlingParameterUtil.setDataService(dataService);
        try {
            while (crawlerContext.getStatus() != CrawlerStatus.DONE && isContinue(threadCheckCount)) {
                final UrlQueue<?> urlQueue = urlQueueService.poll(crawlerContext.sessionId);