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

Question

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.

Answer 1

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)
        .map(Map.Entry::getKey)
        .map(field -> String.format("The user's %s cannot be null", field))
        .map(RuntimeException::new)
        .findFirst()
        .ifPresent(e -> {
            throw e;
        });
}

or this briefer version that bypasses the use of method references:

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

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