How to aggregate many marshalled (json) objects to one file - apache-camel

Question

I created a route to buffer/store marshaled objects (json) into files. This route (and the other route to read the buffer) work fine.
storing in buffer:
from(DIRECT_IN).marshal().json().marshal().gzip().to(fileTarget());
reading from buffer:
from(fileTarget()).unmarshal().gzip().unmarshal().json().to("mock:a")
To reduce i/o i want to aggregate many exchanges in one file. I tried to just aggregate after json and before it so i added this after json() or from(...):
.aggregate(constant(true)).completionSize(20).completionTimeout(1000).groupExchanges()
In both cases i get conversion exceptions. How to do it correctly? I would prefer a way without custom aggregator. And it would be nice if just many exchanges/object are aggregated in one json (as list of objects) or in one text file - one json object per line.
Thanks in advance.

Answer 1

Meanwhile i added a simple aggreagtor:
public class LineAggregator implements AggregationStrategy {
#Override
public final Exchange aggregate(final Exchange oldExchange, final Exchange newExchange) {
//if first message of aggregation
if (oldExchange == null) {
return newExchange;
}
//else aggregate
String oldBody = oldExchange.getIn().getBody(String.class);
String newBody = newExchange.getIn().getBody(String.class);
String aggregate = oldBody + System.lineSeparator() + newBody;
oldExchange.getIn().setBody(aggregate);
return oldExchange;
}
}
The routes look like that, to buffer:
from(...)// marshal objects to json
.marshal()
.json()
.aggregate(constant(true), lineAggregator)
.completionSize(BUFFER_PACK_SIZE)
.completionTimeout(BUFFER_PACK_TIMEOUT)
.marshal()
.gzip()
.to(...)
from buffer:
from(...).unmarshal()
.gzip()
.split()
.tokenize("\r\n|\n|\r")
.unmarshal()
.json()
.to(....)
But the question remains, is the aggregator necessary?