### HTTP Client Architecture

```
SwitchableHttpClient (extends FaultTolerantClient)
    ├── Hc5HttpClient (default) - Apache HttpComponents 5.x
    └── Hc4HttpClient (fallback) - Apache HttpComponents 4.x

HcHttpClient (abstract base class)
    ├── Hc4HttpClient
    └── Hc5HttpClient
```

Switch via system property: `-Dfess.crawler.http.client=hc4` or `hc5` (default)