Why spring batch itemWriter has method write with list of data

Why spring batch itemWriter has method write with list of data

I am new in spring batch so maybe I am wrong but I dont understand why
write method in itemWriter need list of data:
void write(List<? extends T> items) throws Exception;
If I understand this process first is itemReader which read list of item.
In first iteration read first item and so on... Next step is itemProcessor
which gets data from itemReader. Then there is some processing and
itemProcessor return new class which we want to save somewhere. So last
step is itemWriter which get this class which return itemProcessor. So I
dont know when itemWriter gets list of data. When I debugging my simple
sample project there is still just one item in this list. Please someone
explain me it
thx a lot