└── fess-crawler-opensearch/  # OpenSearch backend
```

### Key Components

#### Core Engine
- **Crawler**: Main orchestrator managing crawl execution
- **CrawlerContext**: Execution context and configuration
- **CrawlerThread**: Individual crawler thread implementation

#### Client Architecture
- **HcHttpClient**: HTTP/HTTPS client using Apache HttpComponents

                throw new ExecutionTimeoutException("The command execution is timeout: " + cmdList);
            }
        } catch (final CrawlerSystemException e) {
            throw e;
        } catch (final InterruptedException e) {
            if (mt != null && mt.isTeminated()) {
                throw new ExecutionTimeoutException("The command execution is timeout: " + cmdList, e);
            }

    }

    /**
     * Gets the execution time for processing this response.
     *
     * @return the execution time in milliseconds
     */
    public long getExecutionTime() {
        return executionTime;
    }

    /**
     * Sets the execution time for processing this response.
     *
     * @param executionTime the execution time in milliseconds
     */

 * <ol>
 *   <li>Initialization: Sets up the crawler context and initializes the URL filter.</li>
 *   <li>Thread Creation: Creates a group of crawler threads to perform the actual crawling.</li>
 *   <li>Execution: Starts the crawler threads and waits for them to complete.</li>
 *   <li>Cleanup: Deletes the crawled data and clears the URL filter.</li>
 * </ol>
 *

    /**
     * Test rule processor chain behavior
     */
    public void test_ruleProcessorChain() {
        final List<String> executionOrder = new ArrayList<>();

        // Create custom processor that tracks execution
        ResponseProcessor processor = new ResponseProcessor() {
            @Override
            public void process(ResponseData responseData) {
                executionOrder.add("processor_executed");
            }

import org.codelibs.fess.crawler.entity.OpenSearchAccessResult;
import org.codelibs.fess.crawler.entity.OpenSearchAccessResultData;
import org.codelibs.fess.crawler.exception.CrawlingAccessException;
import org.codelibs.fess.crawler.exception.OpenSearchAccessException;
import org.codelibs.fess.crawler.util.OpenSearchResultList;
import org.joda.time.DateTimeZone;
import org.joda.time.format.DateTimeFormatter;

     */
    public void test_concurrentNameChanges() throws Exception {
        final int threadCount = 10;
        final CountDownLatch startLatch = new CountDownLatch(1);
        final CountDownLatch endLatch = new CountDownLatch(threadCount);
        final List<Exception> exceptions = new ArrayList<>();

        ExecutorService executor = Executors.newFixedThreadPool(threadCount);

            fail("Should throw CrawlerSystemException");
        } catch (CrawlerSystemException e) {
            assertEquals("Transform exception", e.getMessage());
        }
    }

    /**
     * Test exception handling in getData
     */
    public void test_exceptionHandling_getData() {

        assertNotNull(exception);
        assertNull(exception.getCause());
        assertNull(exception.getMessage());
    }

    /**
     * Test constructor with various cause types
     */
    public void test_constructor_withVariousCauseTypes() {
        // With Exception cause
        Exception exceptionCause = new Exception("Exception cause");

     */
    public void test_concurrentOperations() throws Exception {
        final int threadCount = 10;
        final int operationsPerThread = 100;
        final CountDownLatch startLatch = new CountDownLatch(1);
        final CountDownLatch endLatch = new CountDownLatch(threadCount);
        final List<Exception> exceptions = new ArrayList<>();

        ExecutorService executor = Executors.newFixedThreadPool(threadCount);