解密Facade与服务层模式：设计模式的结构与架构之辨

// 假设这是子系统中的复杂服务
class ProductAvailabilityService {
    public boolean checkAvailability(List<String> productIds) {
        System.out.println("检查商品库存...");
        // 实际的库存检查逻辑
        return true;
    }
}

class PaymentService {
    public boolean processPayment(String userId, double amount) {
        System.out.println("处理支付...");
        // 实际的支付处理逻辑
        return true;
    }
}

class EmailNotificationService {
    public void sendPurchaseConfirmation(String userId, List<String> productIds) {
        System.out.println("发送购买确认邮件...");
        // 实际的邮件发送逻辑
    }
}

// Facade类，提供简化的接口
public class ShopFacade {
    private ProductAvailabilityService availabilityService;
    private PaymentService paymentService;
    private EmailNotificationService emailService;

    public ShopFacade() {
        this.availabilityService = new ProductAvailabilityService();
        this.paymentService = new PaymentService();
        this.emailService = new EmailNotificationService();
    }

    // 客户端只需调用此方法即可完成购买流程
    public boolean buyProducts(String userId, List<String> productIds, double totalAmount) {
        System.out.println("--- 开始购买流程 ---");
        if (!availabilityService.checkAvailability(productIds)) {
            System.out.println("购买失败：部分商品缺货。");
            return false;
        }
        if (!paymentService.processPayment(userId, totalAmount)) {
            System.out.println("购买失败：支付处理失败。");
            return false;
        }
        emailService.sendPurchaseConfirmation(userId, productIds);
        System.out.println("--- 购买成功，已发送邮件通知 ---");
        return true;
    }

    public static void main(String[] args) {
        ShopFacade shop = new ShopFacade();
        List<String> items = Arrays.asList("Laptop", "Mouse");
        shop.buyProducts("user123", items, 1200.00);
    }
}

// 假设这是底层的数据访问或领域模型
class PatientRepository {
    public Patient getPatientById(String id) { /* ... */ return new Patient(id, "张三"); }
    public List<Prescription> getPrescriptionsForPatient(String patientId) { /* ... */ return Arrays.asList(new Prescription("感冒药")); }
}

class DoctorRepository {
    public Doctor getDoctorById(String id) { /* ... */ return new Doctor(id, "李医生"); }
    public List<Appointment> getDoctorAppointments(String doctorId) { /* ... */ return Arrays.asList(new Appointment("病人A", new Date())); }
}

// 病人服务层
public class PatientService {
    private PatientRepository patientRepo;

    public PatientService() { this.patientRepo = new PatientRepository(); }

    public Patient retrievePatientHistory(String patientId) {
        System.out.println("获取病人历史信息...");
        return patientRepo.getPatientById(patientId); // 实际可能更复杂，涉及多表查询
    }

    public List<Prescription> getCurrentPrescriptions(String patientId) {
        System.out.println("获取病人当前处方...");
        return patientRepo.getPrescriptionsForPatient(patientId);
    }
    // 其他病人相关业务方法，如更新病人信息、添加诊断等
}

// 医生服务层
public class DoctorService {
    private DoctorRepository doctorRepo;

    public DoctorService() { this.doctorRepo = new DoctorRepository(); }

    public List<Appointment> getDoctorAppointments(String doctorId) {
        System.out.println("获取医生预约信息...");
        return doctorRepo.getDoctorAppointments(doctorId);
    }

    public void scheduleAppointment(String doctorId, String patientId, Date time) {
        System.out.println("安排预约...");
        // 实际的预约逻辑，可能涉及事务管理、冲突检测等
    }
    // 其他医生相关业务方法，如更新医生日程、查看病人详情等
}

public class HospitalApplication {
    public static void main(String[] args) {
        PatientService patientService = new PatientService();
        DoctorService doctorService = new DoctorService();

        // 客户端通过服务层调用业务逻辑
        Patient p = patientService.retrievePatientHistory("P001");
        System.out.println("病人姓名: " + p.getName());

        List<Appointment> appointments = doctorService.getDoctorAppointments("D001");
        System.out.println("医生预约: " + appointments.size() + "个");
    }
}