Specification Pattern

복잡한 Domain Logic을 좀 더 이해하기 쉽게 "AND", "OR", "NOT" 의 논리 연산으로 추상화 한다.

복잡한 Logic을 하나 하나 풀어 각각의 Specification으로 정의하고, 각 Specification을 위 "AND", "OR", "NOT" 논리연산으로 연결한다.

public interface Specification {
	Specification and(Specification other);
	Specification or(Specification other);
	Specification not();
	boolean isSatisfiedBy(Object candidate);
}

public abstract class AbstractSpecification implements Specification { 
	public Specification and(Specification other) { 
		return new AndSpecification(this, other); 
	}

	public Specification or(Specification other) { 
		return new OrSpecification(this, other); 
	}

	public Specification not() { 
		return new NotSpecification (this); 
	}
}

public class AndSpecification extends AbstractSpecification { 
	private Specification some; 
	private Specification other; 

	public AndSpecification(Specification some, Specification other) { 
		some = some; 
		other = other; 
	}

	public boolean isSatisfiedBy(Object candidate) { 
		return some.isSatisfiedBy(candidate) && other.isSatisfiedBy(candidate); 
	}
}

public class OrSpecif ication extends AbstractSpecif ication { 
	private Specification some; 
	private Specification other; 

	public OrSpecification(Specification some, Specification other) { 
		some = some; 
		other = other; 
	}

	public boolean isSatisfiedBy(Object candidate) { 
		return some.isSatisfiedBy(candidate) || other.isSatisfiedBy(candidate); 
	}
}

public class NotSpecification extends AbstractSpecification { 
	private Specification wrapped; 

	public NotSpecification(Specification some) { 
		wrapped = some; 
	}

	public boolean isSatisfiedBy(Object candidate) { 
		return !wrapped.isSatisfiedBy(candidate); 
	}
}

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java에서 predicate로 이미 구현되어 있더라...