How to refactor if statements with a Map using Java 8 Lambdas-CodePudding

I would like to know how i can refactor my code using a Map Data Structure and Lambdas.

Here is my method:

private void validateUserFields(User user) {
    if(user.getName() == null){
        throw new RuntimeException("The user's name cannot be null");
    }
    if(user.getLastName() == null){
        throw new RuntimeException("The user's lastName cannot be null");
    }
    if(user.getDni() == null){
        throw new RuntimeException("The user's dni cannot be null");
    }
    if(user.getVehicle() == null){
        throw new RuntimeException("The user's vehicle cannot be null");
    }
}

I expect a elegant an a simple way to refactor my code.

CodePudding user response：

This is what you asked for, I dont't know if it's elegant, your method looks fine as is to me, the only thing I would change is to create an InvalidUserException which takes in the name of the null field.

This can be a good exercise to understand data structures and the Functional Interface, but I wouldn't do it this way for something as simple as this.

You could check out the simplified strategy pattern with lambdas.

EDIT: This could be useful if you have a very complex validation logic on many fields, but simply for checking that no field is null I agree with using the Lombok approach as suggested in the comments.

public class App {
    public static HashMap<String, Predicate<User>> VALIDATION_FUNCTIONS = new HashMap<>();
    static {
        VALIDATION_FUNCTIONS.put("NAME", user -> user.getName() != null);
        VALIDATION_FUNCTIONS.put("MOREFIELDS", user -> user.getMorefields() != null);
    }
    public static void main(String[] args) {
        validateUserFields(new User());
    }
    private static void validateUserFields(User user) {
         VALIDATION_FUNCTIONS.forEach((field,function) -> {
                    if (!function.test(user)) {
                        throw new RuntimeException(field   " is null");
                    }
                }
        );
    }
    @Getter
    @NoArgsConstructor
    static class User {
        private String name;
        private String morefields;
    }
}

CodePudding user response：

Try a map of validations:

private static Map<String, Function<User, ?>> VALIDATIONS = Map.of(
        "name", User::getName,
        "lastName", User::getLastName,
        "dni", User::getDni,
        "vehicle", User::getVehicle
);

private void validateUserFields(User user) {
    VALIDATIONS.entrySet().stream()
        .filter(entry -> entry.getValue().apply(user) == null)
        .findFirst()
        .ifPresent(entry -> {
            throw new RuntimeException("The user's "   entry.getKey()   " cannot be null");
        });
}

I don't know if it's "elegant", but it is scaleable and flexible.