Camel: Poll Enrich with Aggregation

Question

From the camel book, section 'Using pollEnrich to merge additional data with an existing message', it shows that you can merge the oldExchange(from the quarz) with the new one (from ftp).

The problem is that I have a file from a topic(old Exchange) and I use pollEnrich to get a new file from a ftp server and I want to merge this too. I am interested in set some headers from oldExchange to the newExchange.

The problem that I am facing is that the oldExchange is all the time null. I have read the examples from camel book, for aggregator and there said: "The first message arrives for the first group. == null". I don't understand, then where is my oldExchange? the one from the topic. Why only at the second iteration the exchange is not null (for the same group).

from("myTopic")
    .pollEnrich()
    .simple("ftp://myUrl&fileName=${in.headers.test}")
    .aggregate((Exchange oldExchange, Exchange newExchange) -> {
        final String oldHeader = oldExchange.getIn().getHeader("test", String.class);
        newExchange.getIn().setHeader("test", oldHeader);
        return newExchange;
    })

I have read this: http://camel.465427.n5.nabble.com/Split-and-Aggregate-Old-Exchange-is-null-everytime-in-AggregationStrategy-td5746365.html#a5746405 and still I don't understand how can both messages belong to the same group.

Answer 1

@burki true, is it working as you said with the aggregationStrategy inside the pollEnrich() but I need the simple because I am calling an endpoint dynamically and I cannot do this in the pollEnrich (or at least I don't know how).

I was able to solve like this:

from("myTopic")
.pollEnrich()
.simple("ftp://myUrl&fileName=${in.headers.test}")
.aggregationStrategy((Exchange oldExchange, Exchange newExchange) -> {
    final String oldHeader = oldExchange.getIn().getHeader("test", String.class);
    newExchange.getIn().setHeader("test", oldHeader);
    return newExchange;
})

So instead of the .aggregate call, I am using .aggregationStrategy , what I understood is that the .aggregate call is for the standard aggregation (as @burki mentioned) if we want to aggregate multiple messages and the .aggregationStrategy call can be used to merge 2 messages (one of them is from an external service).