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From snowbug <laji.in...@gmail.com>
Subject Re: Why does ExchangeHelper.prepareAggregation modify the in body?
Date Wed, 02 Sep 2009 06:02:39 GMT

Thanks for the explanation, it makes sense, especially for the pipeline
pattern.

Based on your recommendation, looking into setting the exchange property for
storing information that I'd like to persist, I encountered some problem. In
my splitter bean, the split method looks like this (modified for this post
to make the discussion easier):
    @Handler
    public List<MyMessage> split(Exchange exchange) throws Exception {
        MyMessage msg = (MyMessage) exchange.getIn().getBody();
        exchange.setProperty("myheader", msg.getHeader());

        List<MyMessage> splitted = new ArrayList<MyMessage>();
        for (int i=0; i<5; i++) {
            // create a new message 
            MyMessage part = messageUtil.newMsg(msg);
            part.getBody().setId(i);
            splitted.add(part);
        }

        return splitted;
    }

What I found is that the property I set "myheader" is not preserved in the
next endpoint where the splitted method is processed. It seems that the
splitter used a copy of the exchange when invoking this method, thus any
header I set to the exchange is lost when the copy is discarded.


So any workaround for me to preserve some information? What I can think of
is to add a bean processing after the previous step to create the "myheader"
property before hitting split (haven't tried but should work), but I'd like
to know if there is any easier approach, or if I am doing anything wrong -
I'm quite new to Camel.

BTW, I think it's shouldn't be rare to have the need to preserve the
original message during the processing of generating the response. One often
need to correlate the response with the original message.
Thanks, Alan
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