设计模式之工厂方法模式

在工厂方法模式中，工厂父类负责定义创建产品对象的公共接口，而工厂子类则负责生成具体的产品对象，这样做的目的是将产品类的实例化操作延迟到工厂子类中完成，即通过工厂子类来确定究竟应该实例化哪一个具体产品类。

使用场景

• 我们不能预测要创建类的具体对象
• 我们想要一个类的子类来指定需要创建的对象
• 当类将创建对象的职责委托给多个帮助子类中的某一个，并且你希望将哪一个帮助子类是代理者这一信息局部化的时候。

知名工厂方法类

• java.util.Calendar
• java.util.ResourceBundle
• java.text.NumberFormat
• java.nio.charset.Charset
• java.net.URLStreamHandlerFactory
• java.util.EnumSet
• javax.xml.bind.JAXBContext

实例

/**
 * 
 * 定义一个包含生产对象方法的接口
 * 
 */
public interface Blacksmith {

  Weapon manufactureWeapon(WeaponType weaponType);

}

/**
 * 
 * 创建新对象的具体子类
 * 
 */
public class OrcBlacksmith implements Blacksmith {

  public Weapon manufactureWeapon(WeaponType weaponType) {
    return new OrcWeapon(weaponType);
  }
}

/**
 * 
 * 创建新对象的具体子类
 * 
 */
public class ElfBlacksmith implements Blacksmith {

  public Weapon manufactureWeapon(WeaponType weaponType) {
    return new ElfWeapon(weaponType);
  }

}

/**
 * 
 * 武器类型枚举
 * 
 */
public enum WeaponType {

  SHORT_SWORD("short sword"), SPEAR("spear"), AXE("axe"), UNDEFINED("");

  private String title;

  WeaponType(String title) {
    this.title = title;
  }

  @Override
  public String toString() {
    return title;
  }
}

/**
 * 
 * 武器接口
 * 
 */
public interface Weapon {

  WeaponType getWeaponType();

}

/**
 * 
 * 兽族武器
 * 
 */
public class OrcWeapon implements Weapon {

  private WeaponType weaponType;

  public OrcWeapon(WeaponType weaponType) {
    this.weaponType = weaponType;
  }

  @Override
  public String toString() {
    return "Orcish " + weaponType;
  }

  @Override
  public WeaponType getWeaponType() {
    return weaponType;
  }
}

/**
 * 
 * 精灵族武器
 * 
 */
public class ElfWeapon implements Weapon {

  private WeaponType weaponType;

  public ElfWeapon(WeaponType weaponType) {
    this.weaponType = weaponType;
  }

  @Override
  public String toString() {
    return "Elven " + weaponType;
  }

  @Override
  public WeaponType getWeaponType() {
    return weaponType;
  }
}

/**
 * 
 * 创建一个APP实例，它可以指示铁匠去铸造战争所使用的武器
 * APP 不关心它使用的是哪一个铁匠
 * APP使用配置或者根据战争的种族决定 
 * 
 */
 public class App {

  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);

  private final Blacksmith blacksmith;
  

  public App(Blacksmith blacksmith) {
    this.blacksmith = blacksmith;
  }
  
  public static void main(String[] args) {
    // 让我们使用兽族的武器去战斗吧
    App app = new App(new OrcBlacksmith());
    app.manufactureWeapons();
    
    // 让我们使用精灵族的武器去战斗吧
    app = new App(new ElfBlacksmith());
    app.manufactureWeapons();
  }
  
  private void manufactureWeapons() {
    Weapon weapon;
    weapon = blacksmith.manufactureWeapon(WeaponType.SPEAR);
    LOGGER.info(weapon.toString());
    weapon = blacksmith.manufactureWeapon(WeaponType.AXE);
    LOGGER.info(weapon.toString());
  }
}

输出结果

08:18:45.512 [main] INFO com.iluwatar.factory.method.App - Orcish spear
08:18:45.517 [main] INFO com.iluwatar.factory.method.App - Orcish axe
08:18:45.518 [main] INFO com.iluwatar.factory.method.App - Elven spear
08:18:45.518 [main] INFO com.iluwatar.factory.method.App - Elven axe