Obtain a data map with list of product name by category

ProductCategory.java

    @RequestMapping("/product-category")
    Map<String, List<String>> getProductsByCategory(List<Product> productList) {
        return productRepos.findAll().stream().collect(Collectors.groupingBy(com.mycompany.functional.programming.
                        exercises.models.Product::getCategory, Collectors.mapping(product -> product.getName(),
                Collectors.toList())));
    }