retrieve registered extensions by instance type

histream-core/src/main/java/de/sekmi/histream/ObservationFactory.java

@@ -38,6 +38,8 @@ public interface ObservationFactory {
 	 */
 	void registerExtension(Extension<?> extension);
 	
+	<T> Extension<T> getExtension(Class<T> type);
+
 	/**
 	 * Get a list of currently registered extensions
 	 * @return currently registered extensions

histream-core/src/main/java/de/sekmi/histream/impl/ObservationFactoryImpl.java

@@ -190,5 +190,14 @@ public class ObservationFactoryImpl implements ObservationFactory{
 			}
 		};
 	}
+	@SuppressWarnings("unchecked")
+	@Override
+	public <T> Extension<T> getExtension(Class<T> extensionType) {
+		ExtensionEntry e = extensions.get(extensionType);
+		if( e == null ){
+			return null;
+		}
+		return (Extension<T>) e.extension;
+	}
 
 }