org.springframework.data.domain.PageImpl cannot be cast to

Question

New to Java. In my project I was getting data by findAll(spec) like this:

public interface ProductRepository extends JpaRepository<Product, Long> {
    List<Product> findAll(Specification<Product> spec);

and in the controller, I was converting response into DTOs like this: (ProductResponse is a DTO)

private List<ProductResponse> convertProductListToResponse(List<Product> products) {

    List<ProductResponse> productResponseList = new ArrayList<ProductResponse>();
    for(int i = 0; i < products.size(); i++) {
        ProductResponse productResponse = new ProductResponse();
            productResponse.convert(products.get(i));
            productResponseList.add(productResponse);
    }

    return productResponseList;

}

@PostMapping("getProducts/{page}")
public List<ProductResponse> getAllProducts(@PathVariable("page") int page) {
    ProductSpecification nameSpecification = new ProductSpecification(new SearchCriteria("title", ":", "First Product"));
    // Service simply uses repository method:
    List<Product> filterProducts = productService.findAll(Specification.where(nameSpecification));

    List<ProductResponse> productResponseList = this.convertProductListToResponse(filterProducts);
    return productResponseList;
}

Than I decided to get data with pagination so I changed the repository:

public interface ProductRepository extends PagingAndSortingRepository<Product, Long> {
     List<Product> findAll(Specification<Product> spec, Pageable pageable);

Now I get the following error:

java.lang.ClassCastException: org.springframework.data.domain.PageImpl cannot be cast to com.vendo.app.entity.Product

Than I output the response (filterProducts) directly in the controller and found a response structured like this:

[ { "content": [
        { "id": 1, "deleted": false, "title": "First Product", ...
        ....// array of product objects

I really don't understand, how can a method with response type of List return such a response? How can I get list of products from this response and convert into DTOs?

Thank you.

Answer 1

在findAll方法中，您应该返回Page<Product>而不是List<Product>

Answer 2

Basically default findAll has 2 variants

Simple if you want to convert Page<Product> to List<Product>

productRepository.findAll(PageRequest.of(0, count)).toList();

Answer 3

By the help of KamilW , I realized that my mistake was using List instead of Page for return type of findAll.

Repository should be as follows:

  Page<Product> findAll(Specification<Product> spec, Pageable pageable);

and controller should be as follows:

    @PostMapping("getProducts/{page}")
public List<ProductResponse> getAllProducts(@PathVariable("page") int page) {

    Pageable productPageable = PageRequest.of(0, page);

    ProductSpecification nameSpecification = new ProductSpecification(new SearchCriteria("title", ":", "First Product"));

    Page<Product> filterProducts = productService.findAll(Specification.where(nameSpecification), productPageable);

    List<ProductResponse> productResponseList = this.convertProductListToResponse(filterProducts.getContent());
    return productResponseList;
}