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Option	Default	Description
correlationExpression		Mandatory Expression which evaluates the correlation key to use for aggregation. The Exchange which has the same correlation key is aggregated together. If the correlation key could not be evaluated an Exception is thrown. You can disable this by using the `ignoreBadCorrelationKeys` option.
aggregationStrategy		Mandatory `AggregationStrategy` which is used to merge the incoming Exchange with the existing already merged exchanges. At first call the `oldExchange` parameter is `null`. On subsequent invocations the `oldExchange` contains the merged exchanges and `newExchange` is of course the new incoming Exchange. From Camel 2.9.2 onwards the strategy can also be a `TimeoutAwareAggregationStrategy` implementation, supporting the timeout callback, see further below for more details. From Camel 2.16 onwards the strategy can also be a `PreCompletionAwareAggregationStrategy` implementation which then runs the completion check in pre-completion mode. See further below for more details.
strategyRef		A reference to lookup the `AggregationStrategy` in the Registry. From Camel 2.12 onwards you can also use a POJO as the `AggregationStrategy`, see further below for details.
strategyMethodName		Camel 2.12: This option can be used to explicit declare the method name to use, when using POJOs as the `AggregationStrategy`. See further below for more details.
strategyMethodAllowNull	`false`	Camel 2.12: If this option is `false` then the aggregate method is not used for the very first aggregation. If this option is `true` then `null` values is used as the `oldExchange` (at the very first aggregation), when using POJOs as the `AggregationStrategy`. See further below for more details.
completionSize		Number of messages aggregated before the aggregation is complete. This option can be set as either a fixed value or using an Expression which allows you to evaluate a size dynamically - will use `Integer` as result. If both are set Camel will fallback to use the fixed value if the Expression result was `null` or `0`.
completionTimeout		Time in millis that an aggregated exchange should be inactive before its complete. This option can be set as either a fixed value or using an Expression which allows you to evaluate a timeout dynamically - will use `Long` as result. If both are set Camel will fallback to use the fixed value if the Expression result was `null` or `0`. You cannot use this option together with completionInterval, only one of the two can be used.
completionInterval		A repeating period in millis by which the aggregator will complete all current aggregated exchanges. Camel has a background task which is triggered every period. You cannot use this option together with completionTimeout, only one of them can be used.
completionPredicate		A Predicate to indicate when an aggregated exchange is complete. Starting in Camel 2.15, if this is not specified and the AggregationStrategy object implements Predicate, the aggregationStrategy object will be used as the completionPredicate.
completionFromBatchConsumer	`false`	This option is if the exchanges are coming from a Batch Consumer. Then when enabled the Aggregator2 will use the batch size determined by the Batch Consumer in the message header `CamelBatchSize`. See more details at Batch Consumer. This can be used to aggregate all files consumed from a File endpoint in that given poll.
forceCompletionOnStop	`false`	Camel 2.9 Indicates to complete all current aggregated exchanges when the context is stopped
completeAllOnStop	`false`	Camel 2.16: Indicates to wait to complete all current and partial (pending) aggregated exchanges when the context is stopped. This also means that we will wait for all pending exchanges which are stored in the aggregation repository to complete so the repository is empty before we can stop. You may want to enable this when using the memory based aggregation repository that is memory based only, and do not store data on disk. When this option is enabled, then the aggregator is waiting to complete all those exchanges before its stopped, when stopping CamelContext or the route using it.
eagerCheckCompletion	`false`	Whether or not to eager check for completion when a new incoming Exchange has been received. This option influences the behavior of the `completionPredicate` option as the Exchange being passed in changes accordingly. When `false` the Exchange passed in the Predicate is the aggregated Exchange which means any information you may store on the aggregated Exchange from the `AggregationStrategy` is available for the Predicate. When `true` the Exchange passed in the Predicate is the incoming Exchange, which means you can access data from the incoming Exchange.
groupExchanges	`false`	If enabled then Camel will group all aggregated Exchanges into a single combined `org.apache.camel.impl.GroupedExchange` holder class that holds all the aggregated Exchanges. And as a result only one Exchange is being sent out from the aggregator. Can be used to combine many incoming Exchanges into a single output Exchange without coding a custom `AggregationStrategy` yourself. Important: This option does not support persistent repository with the aggregator. See further below for an example and more details.
ignoreInvalidCorrelationKeys	`false`	Whether or not to ignore correlation keys which could not be evaluated to a value. By default Camel will throw an Exception, but you can enable this option and ignore the situation instead.
closeCorrelationKeyOnCompletion		Whether or not too late Exchanges should be accepted or not. You can enable this to indicate that if a correlation key has already been completed, then any new exchanges with the same correlation key be denied. Camel will then throw a `closedCorrelationKeyException` exception. When using this option you pass in a `integer` which is a number for a LRUCache which keeps that last X number of closed correlation keys. You can pass in 0 or a negative value to indicate a unbounded cache. By passing in a number you are ensured that cache won't grow too big if you use a log of different correlation keys.
discardOnCompletionTimeout	`false`	Camel 2.5: Whether or not exchanges which complete due to a timeout should be discarded. If enabled then when a timeout occurs the aggregated message will not be sent out but dropped (discarded).
aggregationRepository		Allows you to plugin you own implementation of `org.apache.camel.spi.AggregationRepository` which keeps track of the current inflight aggregated exchanges. Camel uses by default a memory based implementation.
aggregationRepositoryRef		Reference to lookup a `aggregationRepository` in the Registry.
parallelProcessing	`false`	When aggregated are completed they are being send out of the aggregator. This option indicates whether or not Camel should use a thread pool with multiple threads for concurrency. If no custom thread pool has been specified then Camel creates a default pool with 10 concurrent threads.
executorService		If using `parallelProcessing` you can specify a custom thread pool to be used. In fact also if you are not using `parallelProcessing` this custom thread pool is used to send out aggregated exchanges as well.
executorServiceRef		Reference to lookup a `executorService` in the Registry
timeoutCheckerExecutorService		Camel 2.9: If using either of the `completionTimeout`, `completionTimeoutExpression`, or `completionInterval` options a background thread is created to check for the completion for every aggregator. Set this option to provide a custom thread pool to be used rather than creating a new thread for every aggregator.
timeoutCheckerExecutorServiceRef		Camel 2.9: Reference to lookup a `timeoutCheckerExecutorService` in the Registry
optimisticLocking	`false`	Camel 2.11: Turns on using optimistic locking, which requires the `aggregationRepository` being used, is supporting this by implementing the `org.apache.camel.spi.OptimisticLockingAggregationRepository` interface.
optimisticLockRetryPolicy		Camel 2.11.1: Allows to configure retry settings when using optimistic locking.

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In this example we want to aggregate all incoming messages and after 3 seconds of inactivity we want the aggregation to complete. This is done using the completionTimeout option as shown:

Wiki Markup
{snippet:id=e1\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/aggregator/AggregateSimpleTimeoutTest.java}