OpenHub uses Apache Camel events concept:

all Camel events extend java.util.EventObject resp. org.apache.camel.management.event.AbstractExchangeEvent. There are many events already defined in Camel, e.g. ExchangeCompletedEvent, ExchangeFailedEvent, ExchangeSendingEvent etc. These events are generated automatically by Camel.
if you want to catch these events then you have to implement EventNotifier interface and this notifier add to Camel context. It's possible to use method addEventNotifier in class AbstractBasicRoute for our routes.

Usage example: EventNotifier to log details about all sent Exchanges

There are new events defined in OpenHub framework which can be caught anywhere by EventNotifier:

ProcessingMsgAsynchEvent
WaitingMsgAsynchEvent
PartlyFailedMsgAsynchEvent
FailedMsgAsynchEvent
CompletedMsgAsynchEvent

There was discussion if use Spring or Camel events. Finally we use Camel events because we use native support in Camel with lot of predefined events and Spring framework is only one implementation of bean registry and therefore we didn't want to be dependant on specific implementation.

Usage

There is @EventNotifier annotation that marks classes which implement org.apache.camel.spi.EventNotifier interface for listening to Camel events.

EventNotifier implementations have special behaviour in Camel, most of them are Camel services with well-defined lifecycle. Use parent class EventNotifierBase to meet these requirements.

If event notifier extends EventNotifierBase class then it's not necessary to initialize them in Camel context, it's automatically by default.

Custom event:

/**
 * Event for failed VF call. This event occurs when asynch. message with calling VF failed.
 */
public class FailedFromVfEvent extends FailedMsgAsynchEvent {
	private static final long serialVersionUID = 8376176024372186281L;
 
    /**
     * Creates new event.
     *
     * @param exchange the exchange
     * @param message  the message
     */
	public FailedFromVfEvent(Exchange exchange, Message message) {
        super(exchange, message);
	}
}

Event throwing, method notifyFailedFromVf:

/**
 * Helper class for creating events.
 */
public final class CustomEventHelper {
    private CustomEventHelper() {
    }
 
    /**
     * Throws {@link FailedFromVfEvent} and notifies all registered event notifiers.
     *
     * @param exchange the exchange
     */
	public static void notifyFailedFromVf(Exchange exchange) {
        AsynchEventHelper.notifyMsg(exchange, new EventNotifierCallback() {
            @Override
            public boolean ignore(EventNotifier notifier) {
                return notifier.isIgnoreExchangeEvents() || notifier.isIgnoreExchangeCompletedEvent();
            }
            @Override
            public AbstractAsynchEvent createEvent(Exchange exchange) {
                return new FailedFromVfEvent(exchange, getMsgFromExchange(exchange));
            }
        });
	}
 
    private static Message getMsgFromExchange(Exchange exchange) {
        return (Message) exchange.getIn().getHeader(AsynchConstants.MSG_HEADER);
    }
}

Notifier implementation:

/**
 * Event notifier for listening to {@link FailedFromVfEvent} events.
 */
@EventNotifier
public class VfTopUpFailedEventNotifier extends EventNotifierBase<FailedFromVfEvent> {
 
    @Override
    public void doNotify(FailedFromVfEvent event) throws Exception {
        Message message = event.getExchange().getIn().getHeader(AsynchConstants.MSG_HEADER, Message.class);
        if ("createTopUp".equals(message.getOperationName())) {
            getProducerTemplate().send(CreateTopUpRoute.URI_CREATE_TOP_UP_VF_FAILED, event.getExchange());
        }
    }
}

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