### Multi-Instance Crawling

```java
// Create multiple crawler instances
Crawler crawler1 = container.getComponent("crawler");
crawler1.setSessionId("session1");
crawler1.addUrl("https://site1.com");

Crawler crawler2 = container.getComponent("crawler");  
crawler2.setSessionId("session2");
crawler2.addUrl("https://site2.com");

// Execute concurrently
crawler1.setBackground(true);
crawler2.setBackground(true);

        accessResult1.setMethod("GET");
        accessResult1.setMimeType("text/plain");
        accessResult1.setParentUrl("http://www.parent.com/");
        accessResult1.setRuleId("htmlRule");
        accessResult1.setSessionId("id1");
        accessResult1.setStatus(200);
        accessResult1.setUrl("http://www.id1.com/");

        dataService.store(accessResult1);

        urlQueue.setSessionId("id1");
        urlQueue.setUrl("http://www.id1.com/");

        urlQueueService.insert(urlQueue);

        final OpenSearchUrlQueue urlQueue2 = new OpenSearchUrlQueue();
        urlQueue2.setCreateTime(System.currentTimeMillis());
        urlQueue2.setDepth(1);
        urlQueue2.setMethod("GET");
        urlQueue2.setSessionId("id2");

    @Override
    public String getSessionId() {
        return sessionId;
    }

    /*
     * (non-Javadoc)
     *
     * @see org.codelibs.fess.crawler.entity.UrlQueue#setSessionId(java.lang.String)
     */
    @Override
    public void setSessionId(final String sessionId) {
        this.sessionId = sessionId;
    }

    /*
     * (non-Javadoc)
     *

        accessResult1.setMethod("GET");
        accessResult1.setMimeType("text/plain");
        accessResult1.setParentUrl("http://www.parent.com/");
        accessResult1.setRuleId("htmlRule");
        accessResult1.setSessionId("id1");
        accessResult1.setStatus(200);
        accessResult1.setUrl("http://www.id1.com/");

        dataService.store(accessResult1);

     */
    @Override
    public void addIncludeUrlFilter(final String sessionId, final String url) {
        final OpenSearchUrlFilter esUrlFilter = new OpenSearchUrlFilter();
        esUrlFilter.setSessionId(sessionId);
        esUrlFilter.setFilterType(INCLUDE);
        esUrlFilter.setUrl(url);
        insert(esUrlFilter, OpType.INDEX);
        includeFilterCache.invalidate(sessionId);
    }

    /**

     */
    public String getSessionId() {
        return sessionId;
    }

    /**
     * Sets the session ID.
     * @param sessionId The session ID.
     */
    public void setSessionId(final String sessionId) {
        this.sessionId = sessionId;
    }

    /**
     * Returns the filter type.
     * @return The filter type.
     */
    public String getFilterType() {

        final Queue<UrlQueueImpl<Long>> urlQueueList = dataHelper.getUrlQueueList(sessionId);
        synchronized (urlQueueList) {
            final UrlQueueImpl<Long> urlQueue = new UrlQueueImpl<>();
            urlQueue.setSessionId(sessionId);
            urlQueue.setMethod(Constants.GET_METHOD);
            urlQueue.setUrl(url);
            urlQueue.setDepth(0);
            urlQueue.setCreateTime(SystemUtil.currentTimeMillis());

    public void add(final String sessionId, final String url) {
        if (exists(sessionId, url)) {
            return;
        }
        final OpenSearchUrlQueue urlQueue = new OpenSearchUrlQueue();
        urlQueue.setSessionId(sessionId);
        urlQueue.setUrl(url);
        urlQueue.setCreateTime(System.currentTimeMillis());
        urlQueue.setLastModified(0L);
        urlQueue.setDepth(0);

        assertNull(crawlerContext.getSessionId());

        crawlerContext.setSessionId("test-session-001");
        assertEquals("test-session-001", crawlerContext.getSessionId());

        crawlerContext.setSessionId(null);
        assertNull(crawlerContext.getSessionId());

        crawlerContext.setSessionId("");
        assertEquals("", crawlerContext.getSessionId());