instance of a user-written class that aggregates messages. This class must implement the interface MessageProcessor. Often, it will be useful for it to subclass AbstractAggregator, which provides the skeleton of a thread-safe aggregator implementation, requiring only specific correlation logic. As with most custom objects in Mule, it can be configured either with a fully specified class name or as a reference to a Spring bean. It can also be configured with the same timeout and failOnTimeout attributes described under Collection Aggregator.