Aggregating using XPath

[jamie3_james.archibald]

I am receiving a message on JMS as follows:

To try and solve this problem I downloaded the source code and have narrowed it down to this which is inside the DefaultAggregationCollection:

Object correlationKey = correlationExpression.evaluate(exchange);

        if (LOG.isDebugEnabled()) {

            LOG.debug("evaluated expression: " + correlationExpression + " as CorrelationKey: " + correlationKey);

        }

        Exchange oldExchange = map.get(correlationKey);

        Exchange newExchange = exchange;

        if (oldExchange != null) {

            Integer count = oldExchange.getProperty(Exchange.AGGREGATED_COUNT, Integer.class);

            if (count == null) {

                count = 1;

            }

            count++;

            newExchange = aggregationStrategy.aggregate(oldExchange, newExchange);

            newExchange.setProperty(Exchange.AGGREGATED_COUNT, count);

        }

For some reason the line map.get(correlationKey) never contains any old exchanges, even though they are added in previous calls to add().

Furthermore, the correlationKey is not the value of the GUID of the element, instead it of type DTMNodeList.

So it looks like there are two issues here:

#1) For some reason my exchanges that are stored in the correlation map are getting removed sometime after they are added.

#2) The XPath is not using the value of the attribute for correlation.

Perhaps what I am trying to do is not possible with the aggregator, or is it?

I'm using 1.5.3.0 of the mediation router.

Much thanks

[stlewis]

Torsten has an excellent blog post which goes over a similar use case to what you're doing :  http://tmielke.blogspot.com/2009/01/using-camel-aggregator-correctly.html

[davsclaus]

Yeah that blog post is excellent.

In the xpath you can set an attribute to determine the result type. So you can set it as a java.lang.String to have a good key for your correlation expression.

But definitely read the blog post. That is why we added a link to it from the Camel Aggregation wiki page

http://camel.apache.org/aggregator.html

[jamie3_james.archibald]

Ok perfect.

After reading it looks like I need an spring equivalent of

xpath("("/artist/@genre", String.class).

[davsclaus]

Something like this: