Writing many lines from one item in FlatFileItemReader

I am using the FlatFileItemWriter to write data read by a reader. Each read item results in writing N lines in the file.
What is the strategy to be used in this case ?

My first idea is to set up a ItemTransformer that transforms the item into a List of N sub-items. The list is passed as a single item to the FlatFileItemWriter.write() method; a FieldSetCreator creates a huge FieldSet containing N*nb_fields_per_sub_item fields, and a LineAggregator creates a String containing N lines (i.e. the returned String contains \n characters), with a double nested loop: (for i=0..N) and for (j=0..nb_fields_per_sub_item).
There is however a problem with this : the FlatFileItemReader increments its the linesWritten counter by one for each written line, even if the line contains \n characters.

I really need to the know the exact number of written lines, as each line of the output file must start with the line number.

Couldn't you just call write multiple times?

In order to call write() multiple times, I would need to write my own ItemWriter that delegates to the FlatFileItemWriter and invokes the FFIW write() method multiple times in my write() method. While this sounds possible, I was wondering if a solution exists, that allows me to use the FFIW as is (without the need to write my own ItemWriter wrapping it) and just configure it with a special FieldSetCreator and LineAggregator that would do the work.

So, do you think writing my own ItemWriter wrapping a FFIW is a better way to go than using the FFIW as is and configure it with home-made FieldSetCreator and LineAggregator components ?

I would wrap the FFIW, the other approach is much more complex I think, and I don't see any problem with the composite writer.