掌握UML类图：使用PlantUML进行系统设计的实战案例研究

@startuml
class Order {
  -orderId: String
  -orderDate: Date
  +calculateTotal(): Double
  +addItem(item: Product, qty: int): void
}
@enduml

@startuml
title 概念模型：电子商务领域

class Customer {
  name
  email
  shippingAddress
}

class Product {
  name
  description
  basePrice
}

class Category {
  name
  description
}

class Order {
  orderNumber
  orderDate
  status
  totalAmount
}

class OrderItem {
  quantity
  unitPrice
  subtotal
}

class Payment {
  paymentMethod
  transactionId
  amount
  timestamp
}

' 关系
Customer "1" -- "0..*" Order : 提出 >
Order "1" *-- "1..*" OrderItem : 包含 >
Product "1" -- "0..*" OrderItem : 出现在 >
Product "0..*" -- "1" Category : 属于 >
Order "1" -- "1..*" Payment : 由...结算 >

note right of Order
  订单代表客户的
  购买意图和交易
end note

@enduml

@startuml
title 规范模型：服务接口

interface IOrderService {
  +createOrder(customerId: String, items: List<OrderItemDTO>): OrderDTO
  +getOrder(orderId: String): OrderDTO
  +updateOrderStatus(orderId: String, status: OrderStatus): boolean
  +calculateOrderTotal(orderId: String): Money
}

interface IPaymentProcessor {
  +processPayment(orderId: String, paymentDetails: PaymentDTO): PaymentResult
  +refundPayment(transactionId: String, amount: Money): RefundResult
}

interface IInventoryService {
  +checkAvailability(productId: String, quantity: int): boolean
  +reserveItems(orderId: String, items: List<ReservationItem>): boolean
  +releaseReservation(orderId: String): void
}

class OrderDTO {
  +orderId: String
  +customerId: String
  +items: List<OrderItemDTO>
  +total: Money
  +status: OrderStatus
}

class OrderItemDTO {
  +productId: String
  +quantity: int
  +unitPrice: Money
}

' 依赖关系
IOrderService ..> IInventoryService : 使用 >
IOrderService ..> IPaymentProcessor : 协调 >
IOrderService ..> OrderDTO : 返回 >

note bottom of IOrderService
  定义订单管理的契约。
  实现方式可能不同（微服务、单体等）
end note

@enduml

@startuml
title 实现模型：Java/Spring Boot类

package com.ecommerce.order.entity {
  class Order {
    -@Id orderId: UUID
    -@ManyToOne customer: Customer
    -@OneToMany(cascade=ALL) items: List<OrderItem>
    -orderDate: LocalDateTime
    -status: OrderStatus
    -totalAmount: BigDecimal
    
    +addItem(product: Product, qty: int): void
    +calculateTotal(): BigDecimal
    +markAsShipped(): void
  }
  
  class OrderItem {
    -@Id itemId: UUID
    -@ManyToOne order: Order
    -@ManyToOne product: Product
    -quantity: int
    -unitPrice: BigDecimal
    
    +getSubtotal(): BigDecimal
  }
  
  enum OrderStatus {
    PENDING
    CONFIRMED
    SHIPPED
    DELIVERED
    CANCELLED
  }
}

package com.ecommerce.payment.service {
  class PaymentService {
    -@Autowired paymentGateway: PaymentGateway
    -@Autowired orderRepository: OrderRepository
    
    +processPayment(orderId: UUID, dto: PaymentRequest): PaymentResponse
    -validatePaymentDetails(dto: PaymentRequest): void
    -updateOrderPaymentStatus(orderId: UUID, status: PaymentStatus): void
  }
  
  interface PaymentGateway {
    +charge(amount: BigDecimal, card: CardDetails): TransactionResult
    +refund(transactionId: String, amount: BigDecimal): RefundResult
  }
}

' 关系
Order "1" *-- "1..*" OrderItem : 组合 >
Order ..> PaymentService : 依赖于 >
PaymentService ..> PaymentGateway : 通过实现 >

note right of OrderItem
  @Entity 注解映射到数据库表。
  Cascade=ALL 确保项目随订单一起持久化。
end note

@enduml

@startuml
class BankAccount {
  +accountNumber: String
  +getBalance(): BigDecimal
  -balance: BigDecimal
  -transactionHistory: List<Transaction>
  #calculateInterest(rate: double): BigDecimal
  ~internalAudit(): void
}

note right of BankAccount
  + 公共：外部客户端的 API
  - 私有：内部状态，外部不可访问
  # 受保护：用于子类扩展
  ~ 包：在同一模块内可见
end note
@enduml

@startuml
class ShoppingCart {
  +addItem(product: Product, qty: int): void
  +removeItem(productId: String): boolean
}

class Product {
  +name: String
  +price: BigDecimal
  +inStock: boolean
}

' 购物车可以包含 0 到多个商品
' 每个商品都恰好引用一个产品
ShoppingCart "1" *-- "0..*" Product : 包含 >

note bottom
  多重性规则：
  • 0..* = 可选，多个（最常见）
  • 1 = 恰好一个（必需）
  • 0..1 = 可选，单个（例如，个人资料图片）
  • 1..* = 至少一个（例如，订单项）
end note
@enduml

@startuml
abstract class Notification {
  #recipient: String
  #message: String
  +abstract send(): boolean
  +logDelivery(): void
}

interface EmailNotification {
  +subject: String
  +send(): boolean
}

interface SMSNotification {
  +phoneNumber: String
  +send(): boolean
}

Notification <|-- EmailNotification
Notification <|-- SMSNotification

note right of Notification
  抽象类：共享状态 + 部分实现
  接口：纯粹契约，支持多重继承
end note
@enduml