CrawlerContext context = new CrawlerContext();
        context.setSessionId("test");
        CrawlingParameterUtil.setCrawlerContext(context);
        assertNotNull(CrawlingParameterUtil.getCrawlerContext());

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

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

 * UrlQueue<?> urlQueue = CrawlingParameterUtil.getUrlQueue();
 * CrawlingParameterUtil.setUrlQueue(newUrlQueue);
 *
 * CrawlerContext context = CrawlingParameterUtil.getCrawlerContext();
 * CrawlingParameterUtil.setCrawlerContext(newContext);
 *
 * UrlQueueService<UrlQueue<?>> urlQueueService = CrawlingParameterUtil.getUrlQueueService();
 * CrawlingParameterUtil.setUrlQueueService(newUrlQueueService);
 *

     */
    @Override
    public void run() {
        log(logHelper, LogType.START_THREAD, crawlerContext);
        int threadCheckCount = 0;
        // set urlQueue to thread
        CrawlingParameterUtil.setCrawlerContext(crawlerContext);
        CrawlingParameterUtil.setUrlQueueService(urlQueueService);
        CrawlingParameterUtil.setDataService(dataService);
        try {

            final String sessionId = "id1";
            urlFilter.init(sessionId);
            crawlerContext.setUrlFilter(urlFilter);
            CrawlingParameterUtil.setCrawlerContext(crawlerContext);
            httpClient.init();
            httpClient.processRobotsTxt(url);
            assertEquals(1, crawlerContext.getRobotsTxtUrlSet().size());

ExtractException (checked)          # Extraction failures
  └─ UnsupportedExtractException
```

### Thread-Local Storage

```java
// Set (in CrawlerThread)
CrawlingParameterUtil.setCrawlerContext(context);
CrawlingParameterUtil.setUrlQueue(urlQueue);

// Get (anywhere in same thread)
CrawlerContext ctx = CrawlingParameterUtil.getCrawlerContext();

// Clear (ALWAYS in finally)

        for (int i = 0; i < crawlerContext.getNumOfThread(); i++) {
            final CrawlerThread crawlerThread = crawlerContainer.getComponent("crawlerThread");
            crawlerThread.setCrawlerContext(crawlerContext);
            crawlerThread.setClientFactory(clientFactory);
            threads[i] =

        crawlerThread.crawlerContainer = crawlerContainer;
        crawlerThread.logHelper = logHelper;
        crawlerThread.setClientFactory(clientFactory);
        crawlerThread.setCrawlerContext(crawlerContext);

        when(crawlerContainer.available()).thenReturn(true);
    }

    /**
     * Test isValid method with a valid URL queue.
     */