spring-batch-demo

You need to be consistent in what the type of the items is that you want to handle on batch level. According to your step definition it is Trade. By calling chunk(1) on the step builder, you declare that your batch should read items of type Trade with a chunk size of 1 (i.e. one at a time) and pass these on to a writer for items of type Trade. In this case, you need to supply a reader of type ItemReader, a writer of type ItemWriter and optionally a processor of type ItemProcessor.

The problem is that your reader is of type ItemReader>, i.e. it does not yield a Trade for each invocation of its read method but a list of trades.

If you want to use the AggregateItemReader you need to wrap it into a custom reader that works as an adapter and actually returns Trade items and not List.

For example, the custom read method could look like this: