CrawlingAccessException (checked)   # Runtime crawl errors
  ├─ MaxLengthExceededException
  └─ ChildUrlsException
ExtractException (checked)          # Extraction failures
  └─ UnsupportedExtractException
```

### Thread-Local Storage

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