建造者模式

• 分离复杂对象的构建和表示
• 同样的构建过程可以创建不同的表示
• 构造函数方法为 private，定义 Builder 类，通过一些方法完善对应属性，调用 build 方法创建对象。

为什么要使用建造者模式

• 对于一个对象构建参数特别多，如果用 new 可能会把参数传递错误。
• 如果类属性之间有一定的依赖关系，使用 Set 方法，无法进行依赖关系和约束条件校验。
• 需要创建不可变对象，对象创建之后，就不能再修改内部的属性值，因此不能暴露 set 方法。

流式建造者模式

public class User {

  private final String firstName;

  private final String lastName;

  private final int age;

  private final String phone;

  private final String address;

  private User(UserBuilder builder) {
    this.firstName = builder.firstName;
    this.lastName = builder.lastName;
    this.age = builder.age;
    this.phone = builder.phone;
    this.address = builder.address;
  }


  public String getFirstName() {
    return firstName;
  }

  public String getLastName() {
    return lastName;
  }

  public int getAge() {
    return age;
  }

  public String getPhone() {
    return phone;
  }

  public String getAddress() {
    return address;
  }

  @Override
  public String toString() {
    return "User{" +
      "firstName='" + firstName + '\'' +
      ", lastName='" + lastName + '\'' +
      ", age=" + age +
      ", phone='" + phone + '\'' +
      ", address='" + address + '\'' +
      '}';
  }

  public static class UserBuilder {
    private final String firstName;

    private final String lastName;

    private int age;

    private String phone;

    private String address;

    public UserBuilder(String firstName, String lastName) {
      this.firstName = firstName;
      this.lastName = lastName;
    }

    public UserBuilder age(int age) {
      this.age = age;
      return this;
    }

    public UserBuilder phone(String phone) {
      this.phone = phone;
      return this;
    }

    public UserBuilder address(String address) {
      this.address = address;
      return this;
    }

    public User builder() {
      User user = new User(this);
      validateUserObject(user);
      return user;
    }

    private void validateUserObject(User user) {
    }

  }
}

经典建造者模式

public interface IMobilePhoneBuilder {
  /**
     * 组装电池
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  void buildBattery();

  /**
     * 组装操作系统
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  void buildOS();

  /**
     * 组装屏幕
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  void buildScreen();

  /**
     * 是否触屏
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:36
     */
  void buildStylus();

  /**
     * 获取实体
     * @return MobilePhone
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:50
     */
  MobilePhone builder();
}

public class AndroidPhoneBuilder implements IMobilePhoneBuilder {

  // 手机实体
  private MobilePhone mobilePhone;

  public AndroidPhoneBuilder() {
    this.mobilePhone = new MobilePhone("Android Phone!");
  }


  /**
     * 组装电池
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildBattery() {
    mobilePhone.setPhoneBattery(BatteryType.MAH_1500);
  }

  /**
     * 组装操作系统
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildOS() {
    mobilePhone.setOperationSystemType(OperationSystemType.ANDROID);
  }

  /**
     * 组装屏幕
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildScreen() {
    mobilePhone.setPhoneScreenType(ScreenType.SCREEN_TYPE_TOUCH_RESISTIVE);
  }

  /**
     * 是否触屏
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:36
     */
  @Override
  public void buildStylus() {
    mobilePhone.setStylusType(StylusType.YES);
  }

  /**
     * 获取实体
     * @return MobilePhone
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:50
     */
  @Override
  public MobilePhone builder() {
    return this.mobilePhone;
  }
}

public class WindowsPhoneBuilder implements IMobilePhoneBuilder {

  private MobilePhone mobilePhone;

  public WindowsPhoneBuilder() {
    this.mobilePhone = new MobilePhone("Windows Phone");
  }

  /**
     * 组装电池
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildBattery() {
    mobilePhone.setPhoneBattery(BatteryType.MAH_1000);
  }

  /**
     * 组装操作系统
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildOS() {
    mobilePhone.setOperationSystemType(OperationSystemType.WINDOWS_PHONE);
  }

  /**
     * 组装屏幕
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:35
     */
  @Override
  public void buildScreen() {
    mobilePhone.setPhoneScreenType(ScreenType.SCREEN_TYPE_TOUCH_CAPACITIVE);
  }

  /**
     * 是否触屏
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:36
     */
  @Override
  public void buildStylus() {
    mobilePhone.setStylusType(StylusType.YES);
  }

  /**
     * 获取实体
     * @return MobilePhone
     * @author HoldDie
     * @email HoldDie@163.com
     * @date 2018/5/25 10:50
     */
  @Override
  public MobilePhone builder() {
    return this.mobilePhone;
  }
}

public class Manufacturer {

  public void construct(IMobilePhoneBuilder phoneBuilder){
    phoneBuilder.buildBattery();
    phoneBuilder.buildOS();
    phoneBuilder.buildScreen();
    phoneBuilder.buildStylus();
  }
}

@Data
public class MobilePhone {

  private String phoneName;

  private ScreenType phoneScreenType;

  private BatteryType phoneBattery;

  private OperationSystemType operationSystemType;

  private StylusType stylusType;

  public MobilePhone(String s) {
    this.phoneName = s;
  }
}

public static void main(String[] args) {

  System.out.println("Hello World!");

  Manufacturer manufacturer = new Manufacturer();

  // 构建一个安卓系统
  IMobilePhoneBuilder androidPhoneBuilder = new AndroidPhoneBuilder();

  manufacturer.construct(androidPhoneBuilder);

  System.out.println(androidPhoneBuilder.builder().getOperationSystemType());

  // 构建一个 windows 系统
  WindowsPhoneBuilder windowsPhoneBuilder = new WindowsPhoneBuilder();

  manufacturer.construct(windowsPhoneBuilder);

  System.out.println(windowsPhoneBuilder.builder().getPhoneName());

}

和工厂模式的区别

• 两者主要是在创建对象的的关注点上不同。
• 工厂模式：用来创建不同但是相关类型的对象（继承同一父类或者接口的一组子类），由给定的参数来决定创建哪种类型的对象。
• 建造者模式：创建一种类型的复杂对象，通过设置不同的可选参数，“定制化”地创建不同的对象。