if (getLogger().isDebugEnabled()) {
                getLogger().debug("ExtractData: {}", extractData);
            }
            // meta
            extractData.getKeySet().stream().filter(k -> extractData.getValues(k) != null).forEach(key -> {
                final String[] values = extractData.getValues(key);
                metaDataMap.put(key, values);

                // meta -> content

```java
public class CustomExtractor extends AbstractExtractor {
    @Override
    public ExtractData getText(final InputStream inputStream, final Map<String, String> params) {
        // Custom extraction logic
        ExtractData extractData = new ExtractData();
        // ... implementation
        return extractData;
    }
}

// Register custom extractor

- Implementations: `UrlQueueServiceImpl`, `DataServiceImpl` (in-memory), `OpenSearchDataService` (persistent)

### Processing Pipeline

```
CrawlerThread → Client → ResponseProcessor → Transformer → Extractor → ExtractData
                                                                            ↓
                         ← UrlQueueService ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← ←
                         ← DataService ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← ← ←