Cannot understand why this method is unresolved

Question

I am studying Spring with Spring In Action book, i have the code from the book where it works fine:

@Slf4j
@Controller
@RequestMapping("/design")
public class DesignTacoController {
    @GetMapping
    public String showDesignForm(Model model) {
        List<Ingredient> ingredients = Arrays.asList(
                new Ingredient("FLTO", "Flour Tortilla", Type.WRAP),
                new Ingredient("COTO", "Corn Tortilla", Type.WRAP),
                new Ingredient("GRBF", "Ground Beef", Type.PROTEIN),
        );

        Type[] types = Ingredient.Type.values();
        for (Type type : types) {
            model.addAttribute(type.toString().toLowerCase(),
                    filterByType(ingredients, type));
        }

        model.addAttribute("design", new Taco());
        return "design";
    }
} 

but when i typed it in my IDEA it says that method filterByType cannot be resolved, but there is no such problem in the book, and no any comment about this problem. I am new in the Spring, tried google a lot, but couldn't find any information about this problem and it source. Could you help me with this problem, a cannot move further because of it. screenshot from IDEA

Answer 1

It looks like this book just contains an error, it does not list the filterByType() method. It's not a Spring method. Here you go:

private List<Ingredient> filterByType(List<Ingredient> ingredients, Type type) {

    return ingredients.stream()
            .filter(x -> x.getType().equals(type))
            .collect(Collectors.toList());

}

Source: Manning Publications