Apply a series of validations to an object using a stream, with subsequent validations only applied if earlier ones succeeded.

GenericValidator.java

package be.objectify.example.validators;

import java.util.LinkedList;
import java.util.List;
import java.util.function.Function;

public class GenericValidator<T> implements Function<T, Boolean> {

    private final List<Function<T, Boolean>> validators = new LinkedList<>();

    public GenericValidator(List<Function<T, Boolean>> validators) {
        this.validators.addAll(validators);
    }
    
    @Override
    public Boolean apply(final T toValidate) {
        final boolean[] guard = {true};
        return validators.stream()
                          .filter(validator -> guard[0])
                          .map(validator -> validator.apply(toValidate))
                          .map(result -> {
                              guard[0] = result;
                              return result;
                          })
                          .reduce(guard[0], (a, b) -> a && b);
    }
}

PersonValidator.java

package be.objectify.example.validators;

import java.util.LinkedList;
import java.util.List;
import java.util.function.Function;

import be.objectify.example.utils.StringUtils;

public class PersonValidator extends GenericValidator<Person> {

    private static final List<Function<Person, Boolean>> VALIDATIONS = new LinkedList<>();

    static {
        VALIDATIONS.add(person -> person != null);
        VALIDATIONS.add(person -> StringUtils.isNotEmpty(person.givenName));
        VALIDATIONS.add(person -> StringUtils.isNotEmpty(person.familyName));
        VALIDATIONS.add(person -> person.gender != null);
    }

    public PersonValidator() {
        super(VALIDATIONS);
    }
}