How to process logically related rows after ItemReader in SpringBatch?

Question

Scenario

To make it simple, let\'s suppose I have an ItemReader that returns me 25 rows.

1. The first 10 rows belong to student A

2. The

Answer 1

because you changed your question i add a new answer

if the students are ordered then there is no need for list/map, you could use exactly one studentObject on the processor to keep the "current" and aggregate on it until there is a new one (read: id change)

if the students are not ordered you will never know when a specific student is "finished" and you'd have to keep all students in a map which can't be written until the end of the complete read sequence

beware:

• the processor needs to know when the reader is exhausted
• its hard to get it working with any commit-rate and "id" concept if you aggregate items that are somehow identical the processor just can't know if the currently processed item is the last one
• basically the usecase is either solved at reader level completely or at writer level (see other answer)

private SimpleItem currentItem;
private StepExecution stepExecution;

@Override
public SimpleItem process(SimpleItem newItem) throws Exception {
    SimpleItem returnItem = null;

    if (currentItem == null) {
        currentItem = new SimpleItem(newItem.getId(), newItem.getValue());
    } else if (currentItem.getId() == newItem.getId()) {
        // aggregate somehow
        String value = currentItem.getValue() + newItem.getValue();
        currentItem.setValue(value);
    } else {
        // "clone"/copy currentItem
        returnItem = new SimpleItem(currentItem.getId(), currentItem.getValue());
        // replace currentItem
        currentItem = newItem;
    }

    // reader exhausted?
    if(stepExecution.getExecutionContext().containsKey("readerExhausted")
            && (Boolean)stepExecution.getExecutionContext().get("readerExhausted")
            && currentItem.getId() == stepExecution.getExecutionContext().getInt("lastItemId")) {
        returnItem = new SimpleItem(currentItem.getId(), currentItem.getValue());
    }

    return returnItem;
}