[5] [接口隔离] ( 1 ) 门面模式 facade

总结

• facade模式有什么用?
  解耦Client和subSystem.
  
  
  
  

• 怎么做到的"解耦Client和subSystem"?
  在Client和subSystem中间加一个facade层,
  facade层负责提供一个统一稳定的交互接口.
  (这就做到了, 无论subSystem怎么变, facede不变, 客户端代码不变)
  .
  
  
  
  

• facade的常见形式?
  facade更注重架构层次看整个系统, 而不是单个类的层次.
  facede很多时候更是一种架构设计模式.
  
  
  

• 非集装箱
  facede简化了客户端和复杂子系统的交互方式,
  但facade并非一个集装箱,任意放进任何多个对象,
  facade组件的内部是"相互耦合关系比较大的一系列组件",
  而不是一个简单的功能集合.
  
  
  

• GOF定义
  为子系统中的一组接口提供一个一致(稳定）的界面，
  Facade模式定义了一个高层接口，
  这个接口使得这一子系统更加容易使用(复用）。
  
  
  

• 场景
  复杂的library
  电商系统...
  
  
  
  
  

java例子1

重构前

package v19_facade.java;

class Projector {
    public void on() {
        System.out.println("Turning on the projector...");
    }

    public void off() {
        System.out.println("Turning off the projector...");
    }
}

class DVDPlayer {
    public void play() {
        System.out.println("Playing the movie...");
    }

    public void stop() {
        System.out.println("Stopping the movie...");
    }
}

class SoundSystem {
    public void on() {
        System.out.println("Turning on the sound system...");
    }

    public void off() {
        System.out.println("Turning off the sound system...");
    }
}

public class Movie1 {
    public static void main(String[] args) {
        Projector projector = new Projector();
        DVDPlayer dvdPlayer = new DVDPlayer();
        SoundSystem soundSystem = new SoundSystem();

        projector.on();
        dvdPlayer.play();
        soundSystem.on();
    }
}

重构后

package v19_facade.java;

class Projector {
    public void on() {
        System.out.println("Turning on the projector...");
    }

    public void off() {
        System.out.println("Turning off the projector...");
    }
}

class DVDPlayer {
    public void play() {
        System.out.println("Playing the movie...");
    }

    public void stop() {
        System.out.println("Stopping the movie...");
    }
}

class SoundSystem {
    public void on() {
        System.out.println("Turning on the sound system...");
    }

    public void off() {
        System.out.println("Turning off the sound system...");
    }
}

class HomeTheaterFacade {
    private Projector projector;
    private DVDPlayer dvdPlayer;
    private SoundSystem soundSystem;

    public HomeTheaterFacade(Projector projector, DVDPlayer dvdPlayer, SoundSystem soundSystem) {
        this.projector = projector;
        this.dvdPlayer = dvdPlayer;
        this.soundSystem = soundSystem;
    }

    public void watchMovie() {
        projector.on();
        dvdPlayer.play();
        soundSystem.on();
    }

    public void stopMovie() {
        projector.off();
        dvdPlayer.stop();
        soundSystem.off();
    }
}

public class Movie2 {
    public static void main(String[] args) {
        Projector projector = new Projector();
        DVDPlayer dvdPlayer = new DVDPlayer();
        SoundSystem soundSystem = new SoundSystem();

        HomeTheaterFacade homeTheater = new HomeTheaterFacade(projector, dvdPlayer, soundSystem);
        homeTheater.watchMovie();
    }
}

java例子2

package v19_facade.java;

// 支付
class Payment {
    private double amount; // 数额

    public Payment(double amount) {
        this.amount = amount;
    }

    public double getAmount() {
        return amount;
    }
}

// 退款状态
enum RefundStatus {
    SUCCESS, FAILURE
}

// 退款相关
class Billing {
    public Payment getPaymentForOrder(int orderId) {
        // Simple Implementation
        return new Payment(50.0);
    }

    public RefundStatus processRefund(Payment payment) {
        // Simple Implementation
        if (payment.getAmount() > 0) {
            return RefundStatus.SUCCESS;
        } else {
            return RefundStatus.FAILURE;
        }
    }
}

// 订单
class Shipping {
    public void updateShippingAddress(int orderId, String newAddress) {
        System.out.println("Shipping address for order " + orderId + " updated to: " + newAddress);
    }
}

// 特殊问题
class Issue {
    private String description;

    public Issue(String description) {
        this.description = description;
    }

    public String getDescription() {
        return description;
    }
}

// 消费者服务
class CustomerService {
    public void notifyCustomer(String message) {
        System.out.println("Notification sent to customer: " + message);
    }

    public void escalateToManager(Issue issue) {
        System.out.println("Issue escalated to manager: " + issue.getDescription());
    }
}

// 外观类
class CustomerSupportFacade {
    private Billing billing;
    private Shipping shipping;
    private CustomerService customerService;

    public CustomerSupportFacade(Billing billing, Shipping shipping, CustomerService customerService) {
        this.billing = billing;
        this.shipping = shipping;
        this.customerService = customerService;
    }

    // 处理退款请求
    public void handleRefundRequest(int orderId) {
        Payment payment = billing.getPaymentForOrder(orderId);
        RefundStatus refundStatus = billing.processRefund(payment);
        customerService.notifyCustomer("Refund status: " + refundStatus);
    }

    // 修改配送地址
    public void changeShippingAddress(int orderId, String newAddress) {
        shipping.updateShippingAddress(orderId, newAddress);
        customerService.notifyCustomer("Shipping address updated");
    }

    // 升级至经理
    public void escalateToManager(Issue issue) {
        customerService.escalateToManager(issue);
    }
}

public class CustomerSuportClient {
    public static void main(String[] args) {
        Billing billing = new Billing();
        Shipping shipping = new Shipping();
        CustomerService customerService = new CustomerService();

        // 外观类
        CustomerSupportFacade customerSupport = new CustomerSupportFacade(billing, shipping, customerService);

        // 给消费者退款
        customerSupport.handleRefundRequest(12345);

        // 修改订单信息
        customerSupport.changeShippingAddress(12345, "123 New Street, New York, NY 10001");

        // 找经理处理问题
        Issue issue = new Issue("Product not working properly");
        customerSupport.escalateToManager(issue);
    }
}