Spring Batch how to regroup/aggregate user datas into a single object - spring

Question

I am trying to transform user operations (like purshases) into a user summary class (expenses by user). A user can have multiple operations but only one summary. I cannot sum purshases in the reader because I need a processor to reject some operation depending to another service.
So some code :
class UserOperation {
String userId;
Integer price;
}
class UserSummary {
String userId;
Long sum;
}
#Bean
public Step retrieveOobClientStep1(StepBuilderFactory stepBuilderFactory, ItemReader<UserOperation> userInformationJdbcCursorItemReader, ItemProcessor<UserOperation, UserSummary> userInformationsProcessor, ItemWriter<UserSummary> flatFileWriter) {
return stepBuilderFactory.get("Step1").<UserOperation, UserSummary>chunk(100) // chunck result that need to be aggregated... not good
.reader(userInformationJdbcCursorItemReader) // read all user operations from DB
.processor(userInformationsProcessor) // I need to reject or not some operations - but here 1 operation = 1 summary that is not good
.writer(flatFileWriter) // write result into flat file
.build();
}
I thing that ItemReader/ItemProcessor/ItemWriter is for single item processing.
But how to regroup multiples records into a single object using Spring Batch ? only Tasklet ?
Possibility but cause problems with small commit interval :
public class UserSummaryAggregatorItemStreamWriter implements ItemStreamWriter<UserSummary>, InitializingBean {
private ItemStreamWriter<UserSummary> delegate;
#Override
public void afterPropertiesSet() throws Exception {
Assert.notNull(delegate, "'delegate' may not be null.");
}
public void setDelegate(ItemStreamWriter<UserSummary> delegate) {
this.delegate = delegate;
}
#Override
public void write(List<? extends UserSummary> items) throws Exception {
Map<String, UserSummary> userSummaryMap = new HashMap<String, UserSummary>();
// Aggregate
for (UserSummary item : items) {
UserSummary savedUserSummary = userSummaryMap.get(item.getUserId());
if (savedUserSummary != null) {
savedUserSummary.incrementSum(item.getSum()); // sum
} else {
savedUserSummary = item;
}
userSummaryMap.put(item.getSubscriptionCode(), savedUserSummary);
}
Collection<UserSummary> values = userSummaryMap.values();
if(values != null) {
delegate.write(new ArrayList<UserSummary>(values));
}
}
#Override
public void open(ExecutionContext executionContext) throws ItemStreamException {
delegate.open(executionContext);
}
#Override
public void update(ExecutionContext executionContext) throws ItemStreamException {
delegate.update(executionContext);
}
#Override
public void close() throws ItemStreamException {
delegate.close();
}
}