DeadEvent considerations - 6.3

Talend ESB Mediation Developer Guide

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6.3
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Talend Data Fabric
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Design and Development
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Talend ESB

Keep in mind that due to the limitations caused by the design of the Guava EventBus, you cannot specify event class to be received by the listener without creating class annotated with @Subscribe method. This limitation implies that endpoint with eventClass option specified actually listens to all possible events (java.lang.Object) and filter appropriate messages programmatically at runtime. The snipped below demonstrates an appropriate excerpt from the Camel code base.

@Subscribe
public void eventReceived(Object event) {
  if (eventClass == null || eventClass.isAssignableFrom(event.getClass())) {
    doEventReceived(event);
...

This drawback of this approach is that EventBus instance used by Camel will never generate com.google.common.eventbus.DeadEvent notifications. If you want Camel to listen only to the precisely specified event (and therefore enable DeadEvent support), use listenerInterface endpoint option. Camel will create dynamic proxy over the interface you specify with the latter option and listen only to messages specified by the interface handler methods. The example of the listener interface with single method handling only SpecificEvent instances is demonstrated below.

package com.example;
 
public interface CustomListener {
 
  @Subscribe
  void eventReceived(SpecificEvent event);
 
}

The listener presented above could be used in the endpoint definition as follows.

from("guava-eventbus:busName?listenerInterface=com.example.CustomListener")
   .to("seda:queue");