【设计模式】JAVA Design Patterns——Abstract-document（抽象文档模式）

public interface Document {
 
  Void put(String key, Object value);
 
  Object get(String key);
 
  <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor);
}
 
public abstract class AbstractDocument implements Document {
 
  private final Map<String, Object> properties;
 
  protected AbstractDocument(Map<String, Object> properties) {
    Objects.requireNonNull(properties, "properties map is required");
    this.properties = properties;
  }
 
  @Override
  public Void put(String key, Object value) {
    properties.put(key, value);
    return null;
  }
 
  @Override
  public Object get(String key) {
    return properties.get(key);
  }
 
  @Override
  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
    return Stream.ofNullable(get(key))
        .filter(Objects::nonNull)
        .map(el -> (List<Map<String, Object>>) el)
        .findAny()
        .stream()
        .flatMap(Collection::stream)
        .map(constructor);
  }
  ...
}

public enum Property {
 
  PARTS, TYPE, PRICE, MODEL
}
 
public interface HasType extends Document {
 
  default Optional<String> getType() {
    return Optional.ofNullable((String) get(Property.TYPE.toString()));
  }
}
 
public interface HasPrice extends Document {
 
  default Optional<Number> getPrice() {
    return Optional.ofNullable((Number) get(Property.PRICE.toString()));
  }
}
public interface HasModel extends Document {
 
  default Optional<String> getModel() {
    return Optional.ofNullable((String) get(Property.MODEL.toString()));
  }
}
 
public interface HasParts extends Document {
 
  default Stream<Part> getParts() {
    return children(Property.PARTS.toString(), Part::new);
  }
}

public class Car extends AbstractDocument implements HasModel, HasPrice, HasParts {
 
  public Car(Map<String, Object> properties) {
    super(properties);
  }
}

    LOGGER.info("Constructing parts and car");
 
    var wheelProperties = Map.of(
        Property.TYPE.toString(), "wheel",
        Property.MODEL.toString(), "15C",
        Property.PRICE.toString(), 100L);
 
    var doorProperties = Map.of(
        Property.TYPE.toString(), "door",
        Property.MODEL.toString(), "Lambo",
        Property.PRICE.toString(), 300L);
 
    var carProperties = Map.of(
        Property.MODEL.toString(), "300SL",
        Property.PRICE.toString(), 10000L,
        Property.PARTS.toString(), List.of(wheelProperties, doorProperties));
 
    var car = new Car(carProperties);
 
    LOGGER.info("Here is our car:");
    LOGGER.info("-> model: {}", car.getModel().orElseThrow());
    LOGGER.info("-> price: {}", car.getPrice().orElseThrow());
    LOGGER.info("-> parts: ");
    car.getParts().forEach(p -> LOGGER.info("\t{}/{}/{}",
        p.getType().orElse(null),
        p.getModel().orElse(null),
        p.getPrice().orElse(null))
    );
 
    // Constructing parts and car
    // Here is our car:
    // model: 300SL
    // price: 10000
    // parts: 
    // wheel/15C/100
    // door/Lambo/300