聊聊dddsample-core的Specification

public interface Specification<T> {

  /**
   * Check if {@code t} is satisfied by the specification.
   *
   * @param t Object to test.
   * @return {@code true} if {@code t} satisfies the specification.
   */
  boolean isSatisfiedBy(T t);

  /**
   * Create a new specification that is the AND operation of {@code this} specification and another specification.
   * @param specification Specification to AND.
   * @return A new specification.
   */
  Specification<T> and(Specification<T> specification);

  /**
   * Create a new specification that is the OR operation of {@code this} specification and another specification.
   * @param specification Specification to OR.
   * @return A new specification.
   */
  Specification<T> or(Specification<T> specification);

  /**
   * Create a new specification that is the NOT operation of {@code this} specification.
   * @param specification Specification to NOT.
   * @return A new specification.
   */
  Specification<T> not(Specification<T> specification);
}

/**
 * Abstract base implementation of composite {@link Specification} with default
 * implementations for {@code and}, {@code or} and {@code not}.
 */
public abstract class AbstractSpecification<T> implements Specification<T> {

  /**
   * {@inheritDoc}
   */
  public abstract boolean isSatisfiedBy(T t);

  /**
   * {@inheritDoc}
   */
  public Specification<T> and(final Specification<T> specification) {
    return new AndSpecification<T>(this, specification);
  }

  /**
   * {@inheritDoc}
   */
  public Specification<T> or(final Specification<T> specification) {
    return new OrSpecification<T>(this, specification);
  }

  /**
   * {@inheritDoc}
   */
  public Specification<T> not(final Specification<T> specification) {
    return new NotSpecification<T>(specification);
  }
}

public class AndSpecification<T> extends AbstractSpecification<T> {

  private Specification<T> spec1;
  private Specification<T> spec2;

  /**
   * Create a new AND specification based on two other spec.
   *
   * @param spec1 Specification one.
   * @param spec2 Specification two.
   */
  public AndSpecification(final Specification<T> spec1, final Specification<T> spec2) {
    this.spec1 = spec1;
    this.spec2 = spec2;
  }

  /**
   * {@inheritDoc}
   */
  public boolean isSatisfiedBy(final T t) {
    return spec1.isSatisfiedBy(t) && spec2.isSatisfiedBy(t);
  }
}

public class OrSpecification<T> extends AbstractSpecification<T> {

  private Specification<T> spec1;
  private Specification<T> spec2;

  /**
   * Create a new OR specification based on two other spec.
   *
   * @param spec1 Specification one.
   * @param spec2 Specification two.
   */
  public OrSpecification(final Specification<T> spec1, final Specification<T> spec2) {
    this.spec1 = spec1;
    this.spec2 = spec2;
  }

  /**
   * {@inheritDoc}
   */
  public boolean isSatisfiedBy(final T t) {
    return spec1.isSatisfiedBy(t) || spec2.isSatisfiedBy(t);
  }
}

public class NotSpecification<T> extends AbstractSpecification<T> {

  private Specification<T> spec1;

  /**
   * Create a new NOT specification based on another spec.
   *
   * @param spec1 Specification instance to not.
   */
  public NotSpecification(final Specification<T> spec1) {
    this.spec1 = spec1;
  }

  /**
   * {@inheritDoc}
   */
  public boolean isSatisfiedBy(final T t) {
    return !spec1.isSatisfiedBy(t);
  }
}