Spring Batch - Aggregating multiple lines in Processor - spring-batch

Question

I am trying to write an Spring Batch application that gets lots of data from a database and writes it to Excel. In this process I need to transpose some data that comes in rows into columns.
So imagine a query that returns:
id,name,value
1, me, 1
1, me, 3
1, me, 2
2, you, 4
3, her, 5
My excel would look like:
1, me, 1, 2, 3
2, you, 4
3, her, 5
Note that when transposing the lines into columns, I also sort the values, so doing this transpose in SQL is a bit tricky.
My idea was to create an ItemReader thar return each line as an object, and then in the Processor consolidate grouping lines into a single object, and an ExcelWriter that gets this DTO and writes to Excel.
To implement the Processor, I would do something like:
private ConsolidatedDTO consolidatedDTO = new ConsolidatedDTO();
public ConsolidatedDTO process(AnaliticDTO item) {
if (consolidatedDTO.getKey().equals(item.getKey)) {
consolidatedDTO.add(item);
} else {
ConsolidatedDTO result = consolidatedDTO;
consolidatedDTO = new ConsolidatedDTO(item);
return result;
}
}
The problem is that I'm returning after consolidating everything, when I receive a different item, but how do I deal with the LAST item? I needed a way to know in the Processor when I received the last item so I could return the consolidated immediately instead of waiting for the next line.
Thanks in advance