观察者模式

观察者模式

• 观察者模式，也叫发布-订阅模式，是一种一对多的关系，一个对象状态发生改变，所有依赖于它的对象都得到通知并被自动更新。

定义事件

// OrderCreatedEvent.java
public static class OrderCreatedEvent extends ApplicationEvent {

    private final String orderId;
    private final String userId;

    public OrderCreatedEvent(Object source, String orderId, String userId) {
        super(source); // source 通常是发布事件的 bean
        this.orderId = orderId;
        this.userId = userId;
    }

    // Getters
    public String getOrderId() { return orderId; }
    public String getUserId() { return userId; }
}

    @Data
    public static class Item{
        private String name;
    }

发布事件

    // OrderService.java
    @Service
    public static class OrderService {

        // Spring 自动注入事件发布器
        @Autowired
        private ApplicationEventPublisher eventPublisher;

        public void createOrder(String userId, List<Item> items) {
            // 1. 创建订单逻辑
            String orderId = saveOrder(userId, items);

            // 2. 发布事件！ 👈 关键步骤
            eventPublisher.publishEvent(
                    new OrderCreatedEvent(this, orderId, userId)
            );

            // 后续逻辑...
        }

        private String saveOrder(String userId, List<Item> items) {
            // 保存到数据库
            return "ORD-" + System.currentTimeMillis();
        }
    }

监听器

    // EmailNotificationListener.java
    @Slf4j
    @Component
    public static class EmailNotificationListener {

//        private static final Logger log = LoggerFactory.getLogger(EmailNotificationListener.class);

        // 监听 OrderCreatedEvent 事件
        @EventListener
        public void handleOrderCreated(OrderCreatedEvent event) {
            log.info("📧 发送邮件通知: 用户 {} 的订单 {} 已创建",
                    event.getUserId(), event.getOrderId());
            // 实际发送邮件逻辑...
        }
    }

监听器

    // SmsNotificationListener.java
    @Component
    public static class SmsNotificationListener {

        @EventListener
        public void handleOrderCreated(OrderCreatedEvent event) {
            System.out.println("📱 发送短信通知: 订单 " + event.getOrderId() + " 已创建");
            // 实际发送短信逻辑...
        }
    }

监听器

    // InventoryUpdateListener.java
    @Component
    public static class InventoryUpdateListener {

        @EventListener
        public void updateInventory(OrderCreatedEvent event) {
            System.out.println("📦 扣减库存: 处理订单 " + event.getOrderId());
            // 扣减商品库存...
        }
    }

完整代码

@RestController
@SpringBootApplication
public class ObserverApplication {

    public static void main(String[] args) {
        SpringApplication.run(ObserverApplication.class, args);
    }

    // OrderCreatedEvent.java
    public static class OrderCreatedEvent extends ApplicationEvent {

        private final String orderId;
        private final String userId;

        public OrderCreatedEvent(Object source, String orderId, String userId) {
            super(source); // source 通常是发布事件的 bean
            this.orderId = orderId;
            this.userId = userId;
        }

        // Getters
        public String getOrderId() { return orderId; }
        public String getUserId() { return userId; }
    }
    @Data
    public static class Item{
        private String name;
    }

    // OrderService.java
    @Service
    public static class OrderService {

        // Spring 自动注入事件发布器
        @Autowired
        private ApplicationEventPublisher eventPublisher;

        public void createOrder(String userId, List<Item> items) {
            // 1. 创建订单逻辑
            String orderId = saveOrder(userId, items);

            // 2. 发布事件！ 👈 关键步骤
            eventPublisher.publishEvent(
                    new OrderCreatedEvent(this, orderId, userId)
            );

            // 后续逻辑...
        }

        private String saveOrder(String userId, List<Item> items) {
            // 保存到数据库
            return "ORD-" + System.currentTimeMillis();
        }
    }
    // EmailNotificationListener.java
    @Slf4j
    @Component
    public static class EmailNotificationListener {

//        private static final Logger log = LoggerFactory.getLogger(EmailNotificationListener.class);

        // 监听 OrderCreatedEvent 事件
        @EventListener
        public void handleOrderCreated(OrderCreatedEvent event) {
            log.info("📧 发送邮件通知: 用户 {} 的订单 {} 已创建",
                    event.getUserId(), event.getOrderId());
            // 实际发送邮件逻辑...
        }
    }
    // SmsNotificationListener.java
    @Component
    public static class SmsNotificationListener {

        @EventListener
        public void handleOrderCreated(OrderCreatedEvent event) {
            System.out.println("📱 发送短信通知: 订单 " + event.getOrderId() + " 已创建");
            // 实际发送短信逻辑...
        }
    }
    // InventoryUpdateListener.java
    @Component
    public static class InventoryUpdateListener {

        @EventListener
        public void updateInventory(OrderCreatedEvent event) {
            System.out.println("📦 扣减库存: 处理订单 " + event.getOrderId());
            // 扣减商品库存...
        }
    }

    @Resource
    OrderService orderService;

    @PostMapping("/create-order")
    public String createOrder(@RequestBody List<Item> items) {
        orderService.createOrder("user-1", items);
        return "订单创建成功！";
    }

}