Offset calculation in Spring Pagination - spring

Question

I have a service with pagination index starting from 1.I get the list of entity after some logic I return the same(responses) as below
totalCount = responses.size();
return new PageImpl<>(responses, pageable, totalCount);
and when I have requested the 1st page as
new PageRequest(1, 100)
I get back the response as
{"content": [
{
"id": "e1",
}{
"id": "2",
}
],
"last": false,
"totalElements": 102,
"totalPages": 2,
"size": 100,
"number": 1,
"sort": null,
"first": true,
"numberOfElements": 2
}
Here even though I have "numberOfElements": 2 I get back "totalElements": 102
The issue which I found is because of pageable.getOffset() calculation in PageImpl
this.total = !content.isEmpty() && pageable != null && pageable.getOffset()
+ pageable.getPageSize() > total
? pageable.getOffset() + content.size() : total;
In my scenario for the 1st Page I'am getting offset as 100 (1*100). How do I resolve this.
Note : I use a third party service to get the responses which is indexed 1 . So I am trying to align my service to that so that the entire logic follow the same indexing.

Answer 1

The result you get is correct, since PageRequest used zero-based pages as stated in the API docs:
Parameters:
page - zero-based page index.
size - the size of the page to be returned.
So that means you're retrieving the second page (not the first one), and since you have a limit of 100 records and a total of 102 records, you'll only retrieve the last two of them.
You can still expose a 1-based number though:
new PageRequest(page-1, 100);
Alternatively, you can customize this by implementing Pageable. This allows you to override the actual offset being used by Spring data.
Nonetheless, this doesn't change the fact that Spring data expects getPageNumber() to be a zero based number. You cannot change that, you can only add an abstraction layer on top of it to make it meet your requirements.

Answer 2

And what's wrong with that? totalElements tells you how many elements are stored within the data source. numberOfElements tells you how many elements the current page contains.
When have 102 elements in total and you requesting page 2 with size 100, you should get exactly the response you received.
What probably confuses you:
With new PageRequest(1, 100) you are requesting the 2nd page as the index starts at 0.