How list of object return a Spring Page with Mongo repository?

I have a GET request in which the user can pass a list of book codes as a parameter. Like this:

@GetMapping("/books")
public ResponseEntity<Page<BooksView>> findAvailableBooks(@RequestParam(value = "codes") String[] codes

I need to take this array of codes and verify which book codes exist in the database and if they are available in stock to return them as a Spring page. I tried this:

1) First check if the code array is filled

2) If so, for each code in the array I check with mongo repository if that code exists in the database and if the available is true

3) If so, I add the current code to a list

4) But I don't know if this logic works (is there a simpler or cleaner way to do it?) and I also don't know how to treat this list so that the return is a Page

public Page<Book> findBooks(String[] codes) {

        if(codes.length > 0) {

            List<String> listOfCodes = null;

            for (String code : codes){

                if(repository.existsByCodeAndAvailable(Long.parseLong(code))){
                   listOfCodes.add(code);
                }
            }

        return ???

        }
}

Solution

you can write custom method in the repository like below,

public interface BookRepository extends MongoRepository<Book, String> {

   Page<Book> findAllByCodeIn(String[] codes, Pageable pageable);
}

you can call the custom method from your service,

bookRepository.findAllByCodeIn(codes, PageRequest.of(0, 10))

I have the below test data inside my db,

bookRepository.save(new Book("S001", "Java"));
bookRepository.save(new Book("S002", "Spring"));
bookRepository.save(new Book("S003", "Kotlin"));

Different test case scenario's

GET http://localhost:8080/books?codes=

{
 "content": [],
 "pageable": {
 "sort": {
   "sorted": false,
   "unsorted": true,
   "empty": true
 },
 "offset": 0,
 "pageNumber": 0,
 "pageSize": 10,
 "paged": true,
 "unpaged": false
},
"totalPages": 0,
"totalElements": 0,
"last": true,
"size": 10,
"number": 0,
"numberOfElements": 0,
"first": true,
"sort": {
  "sorted": false,
  "unsorted": true,
  "empty": true
 },
 "empty": true
}

Test 2:

GET http://localhost:8080/books?codes=S001
{
 "content": [
   {
      "code": "S001",
      "name": "Java"
   }

Test 3:

GET http://localhost:8080/books?codes=S001,S002
{
  "content": [
   {
     "code": "S001",
     "name": "Java"
   },
   {
    "code": "S002",
     "name": "Spring"
   }
 ],