@Override
  public void send (String aRoutingKey, Object aMessage) {
    List<Receiver> list = listeners.get(aRoutingKey);
    Assert.isTrue(list!=null&&list.size()>0,"no listeners subscribed for: " + aRoutingKey);
    for(Receiver receiver : list) {
      receiver.receive(aMessage);
    }
  }
a simple, non-thread-safe implementation of the 
{@link MessageBroker} interface. Useful for testing.

@author Arik Cohen
@since Jul 10, 2016
src/main/java/com/creactiviti/piper/core/messagebroker/SyncMessageBroker.java