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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.camel;
import org.slf4j.LoggerFactory;
/**
* A strategy for aggregating two exchanges together into a single exchange.
*
* On the first invocation of the {@link #aggregate(org.apache.camel.Exchange, org.apache.camel.Exchange) aggregate}
* method the oldExchange parameter is null. The reason is that we have not aggregated anything yet.
* So its only the newExchange that has a value. Usually you just return the newExchange in this
* situation. But you still have the power to decide what to do, for example you can do some alternation on the exchange
* or remove some headers. And a more common use case is for instance to count some values from the body payload. That
* could be to sum up a total amount etc.
*
* Note that oldExchange may be null more than once when this strategy is throwing a
* {@link java.lang.RuntimeException} and parallelProcessing is used. You can work around this behavior using
* the stopOnAggregateException option.
*
* It is possible that newExchange is null which could happen if there was no data possible to
* acquire. Such as when using a PollEnricher to poll from a JMS queue which is empty and a timeout was set.
*
* Important: In the aggregate method, do not create a new exchange instance to return, instead return either the old or
* new exchange from the input parameters; favor returning the old exchange whenever possible.
*
* Possible implementations include performing some kind of combining or delta processing, such as adding line items
* together into an invoice or just using the newest exchange and removing old exchanges such as for state tracking or
* market data prices; where old values are of little use.
*
* If an implementation also implements {@link org.apache.camel.Service} then any
* EIP that allowing configuring a {@link AggregationStrategy} will invoke the
* {@link org.apache.camel.Service#start()} and {@link org.apache.camel.Service#stop()} to control the lifecycle aligned
* with the EIP itself.
*
* If an implementation also implements {@link org.apache.camel.CamelContextAware} then any
* EIP that allowing configuring a {@link AggregationStrategy} will inject the
* {@link org.apache.camel.CamelContext} prior to using the aggregation strategy.
*/
public interface AggregationStrategy {
/**
* Aggregates an old and new exchange together to create a single combined exchange
*
* Important: In the aggregate method, do not create a new exchange instance to return, instead return either the
* old or new exchange from the input parameters; favor returning the old exchange whenever possible.
*
* @param oldExchange the oldest exchange (is null on first aggregation as we only have the new exchange)
* @param newExchange the newest exchange (can be null if there was no data possible to acquire)
* @return a combined composite of the two exchanges, return either the old or new exchange from the
* input parameters; favor returning the old exchange whenever possible)
*/
Exchange aggregate(Exchange oldExchange, Exchange newExchange);
/**
* Aggregates an old and new exchange together to create a single combined exchange.
*
* Important: In the aggregate method, do not create a new exchange instance to return, instead return either the
* old or new exchange from the input parameters; favor returning the old exchange whenever possible.
*
* Important: Only Multicast, Recipient List, and Splitter EIP supports this method with access to the input
* exchange. All other EIPs does not and uses the {@link #aggregate(Exchange, Exchange)} method instead.
*
* @param oldExchange the oldest exchange (is null on first aggregation as we only have the new
* exchange)
* @param newExchange the newest exchange (can be null if there was no data possible to acquire)
* @param inputExchange the input exchange (input to the EIP)
* @return a combined composite of the two exchanges, return either the old or new exchange from the
* input parameters; favor returning the old exchange whenever possible)
*/
default Exchange aggregate(Exchange oldExchange, Exchange newExchange, Exchange inputExchange) {
return aggregate(oldExchange, newExchange);
}
/**
* Indicates if this aggregation strategy uses pre-completion mode.
*
* @return true if this strategy uses pre-completion mode, or false otherwise.
*/
default boolean canPreComplete() {
return false;
}
/**
* Determines if the aggregation should complete the current group, and start a new group, or the aggregation should
* continue using the current group. This callback will only be called if {@link #canPreComplete()} returns
* true.
*
* @param oldExchange the oldest exchange (is null on first aggregation as we only have the new exchange)
* @param newExchange the newest exchange (can be null if there was no data possible to acquire)
* @return true to complete current group and start a new group, or false to keep
* using current
*/
default boolean preComplete(Exchange oldExchange, Exchange newExchange) {
return false;
}
/**
* The aggregated {@link Exchange} has completed
*
* Important: This method must not throw any exceptions.
*
* @param exchange the current aggregated exchange, or the original {@link org.apache.camel.Exchange} if no
* aggregation has been done before the completion occurred
*/
default void onCompletion(Exchange exchange) {
}
/**
* The aggregated {@link Exchange} has completed
*
* Important: This method must not throw any exceptions.
*
* @param exchange the current aggregated exchange, or the original {@link org.apache.camel.Exchange} if no
* aggregation has been done before the completion occurred
* @param inputExchange the input exchange (input to the EIP)
*/
default void onCompletion(Exchange exchange, Exchange inputExchange) {
onCompletion(exchange);
}
/**
* A timeout occurred.
*
* Important: This method must not throw any exceptions.
*
* @param exchange the current aggregated exchange, or the original {@link Exchange} if no aggregation has been done
* before the timeout occurred
* @param index the index, may be -1 if not possible to determine the index
* @param total the total, may be -1 if not possible to determine the total
* @param timeout the timeout value in millis, may be -1 if not possible to determine the timeout
*/
default void timeout(Exchange exchange, int index, int total, long timeout) {
}
/**
* Callback when the aggregated {@link Exchange} fails to add in the
* {@link org.apache.camel.spi.OptimisticLockingAggregationRepository} because of an
* {@link org.apache.camel.spi.OptimisticLockingAggregationRepository.OptimisticLockingException}.
*
* Please note that when aggregating {@link Exchange}'s to be careful not to modify and return the
* {@code oldExchange} from the
* {@link AggregationStrategy#aggregate(org.apache.camel.Exchange, org.apache.camel.Exchange)} method. If you are
* using the default MemoryAggregationRepository this will mean you have modified the value of an object already
* referenced/stored by the MemoryAggregationRepository. This makes it impossible for optimistic locking to work
* correctly with the MemoryAggregationRepository.
*
* You should instead return either the new {@code newExchange} or a completely new instance of {@link Exchange}.
* This is due to the nature of how the underlying {@link java.util.concurrent.ConcurrentHashMap} performs CAS
* operations on the value identity.
*
* @see java.util.concurrent.ConcurrentHashMap
*/
default void onOptimisticLockFailure(Exchange oldExchange, Exchange newExchange) {
LoggerFactory.getLogger(getClass()).trace(
"onOptimisticLockFailure with AggregationStrategy: {}, oldExchange: {}, newExchange: {}", this, oldExchange,
newExchange);
}
}
