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DZone > Java Zone > Fail-fast Validations Using Java 8 Streams

Fail-fast Validations Using Java 8 Streams

Steve Chaloner user avatar by
Steve Chaloner
·
Jan. 15, 15 · Java Zone · Interview
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I’ve lost count of the number of times I’ve seen code which fail-fast validates the state of something, using an approach like

public class PersonValidator {
  public boolean validate(Person person) {
    boolean valid = person != null;
    if (valid) valid = person.givenName != null;
    if (valid) valid = person.familyName != null;
    if (valid) valid = person.age != null;
    if (valid) valid = person.gender != null;
    // ...and many more
  }
}

It works, but it’s a brute force approach that’s filled with repetition due to the valid check. If your code style enforces braces for if statements (+1 for that), your method is also three times longer and growing every time a new check is added to the validator.

Using Java 8’s new stream API, we can improve this by taking the guard condition of if (valid) and making a generic validator that handles the plumbing for you.

import java.util.LinkedList;
import java.util.List;
import java.util.function.Predicate;
 
public class GenericValidator<T> implements Predicate {
 
  private final List<Predicate<T>> validators = new LinkedList<>();
 
  public GenericValidator(List<Predicate<T>> validators) {
    this.validators.addAll(validators);
  }

  @Override
  public boolean test(final T toValidate) {
    return validators.parallelStream()
                     .allMatch(predicate -> predicate.test(toValidate));
  }
} 

Using this, we can rewrite the Person validator to be a specification of the required validations.

public class PersonValidator extends GenericValidator<Person> {

  private static final List<Predicate<Person>> VALIDATORS = new LinkedList<>();

  static {
    VALIDATORS.add(person -> person.givenName != null);
    VALIDATORS.add(person -> person.familyName != null);
    VALIDATORS.add(person -> person.age != null);
    VALIDATORS.add(person -> person.gender != null);
    // ...and many more
  }

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

PersonValidator, and all your other validators, can now focus completely on validation. The behaviour hasn’t changed – the validation still fails fast. There’s no boiler plate, which is A Good Thing.

This one’s going in the toolbox.

Java (programming language) Stream (computing)

Published at DZone with permission of Steve Chaloner, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

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