After upgrading from Apache Camel 2.x to 3.7.2 in our Java 11 project we experience some crudities in a route configuration class, extending the RouteBuilder (Documentation) class. With Camel 2 I used the SimpleExpression ${property[" Exchange.GROUPED_EXCHANGE "]}, which has now been renamed in Camel 3.x to exchangeProperty (Migration Guide). So far, so good.

@Override
public void configure() throws Exception {

    final SimpleExpression documentAppendix =
        new SimpleExpression("${body.appendix}");

    final SimpleExpression groupedExchanges =
        new SimpleExpression("${exchangeProperty["   Exchange.GROUPED_EXCHANGE   "]}");

    from("direct://input")
        .choice()
            .when(documentAppendix)
                .split(documentAppendix, new GroupedExchangeAggregationStrategy())
                .to("direct://input.splitted")
                .end()
                .setBody(groupedExchanges)
                .endChoice()
            .otherwise()
                .setBody(constant(Lists.newArrayList()))
        .end();
    
    // ... omitted
    
}

After running the tests, everything failed because the body did not contain the expected number of appendices. At first, we thought there might be a problem with exchangeProperty but after some time spent with the debugger we've found out the following trail where the property gets "lost":

         GroupedExchangeAggregationStrategy
                         |
                         v
           AbstractListAggregationStrategy
(This class sets the "CamelGroupedExchange" property!)
                         |
                         v
                 AggregateProcessor
                 doAggregation(...)
       ExchangeHelper.preparteAggregation(...)

The expected return after aggregation should be a list of objects, accessible via the CamelGroupedExchange or ${exchangeProperty[" Exchange.GROUPED_EXCHANGE "]} but it gets overridden with the newExchange in ExchangeHelper.preparteAggregation.

As we did not find more evidence, could someone explain this weird behaviour after upgrading Camel to 3.7.2? Maybe there have been breaking changes in ExchangeHelper and the available ExchangePattern/MEP Pattern (CAMEL-13286) but we were not able to break down the issue.

Thanks for your help guys!

CodePudding user response：

We figured out that the AbstractListAggregationStrategy in Camel 3.7.2 now sets the property as In body on completion:

public abstract class AbstractListAggregationStrategy<V> implements AggregationStrategy {
    public AbstractListAggregationStrategy() {
    }

    public abstract V getValue(Exchange exchange);

    public boolean isStoreAsBodyOnCompletion() {
        return true;
    }

    public void onCompletion(Exchange exchange) {
        if (exchange != null && this.isStoreAsBodyOnCompletion()) {
            List<V> list = (List)exchange.removeProperty("CamelGroupedExchange");
            if (list != null) {
                exchange.getIn().setBody(list);
            }
        }

    }

    // omitted

}

With this change our .setBody(groupedExchanges) is redundant and we are able to access the list of exchanges via getIn().