* java -Dfess.crawler.http.client=hc5 ...
 * // or simply
 * java ...
 * }
 * </pre>
 *
 * @author shinsuke
 */
public class SwitchableHttpClient extends FaultTolerantClient {

    private static final Logger logger = LogManager.getLogger(SwitchableHttpClient.class);

    /** System property name to select HTTP client implementation. */
    public static final String HTTP_CLIENT_PROPERTY = "fess.crawler.http.client";

**Fault Tolerance**: `FaultTolerantClient` wrapper (retry, circuit breaker), `SwitchableHttpClient` for HTTP client fallback

---

## Key Components

### Core Classes

- **Crawler** (`Crawler.java`): Main orchestrator - `execute()`, `addUrl()`, `cleanup()`, `stop()`

		instance="prototype">
		<property name="connectionTimeout">15000</property>
		<property name="soTimeout">30000</property>
	</component>
	<component name="httpClient"
		class="org.codelibs.fess.crawler.client.http.SwitchableHttpClient" instance="prototype">
		<property name="hc5Client">internalHttpClient</property>
		<property name="hc4Client">internalHc4HttpClient</property>
		<property name="maxRetryCount">5</property>