设计模式之订阅发布模式

interface Subscriber {
    void update(String message);
}

class Publisher {
    private Map<String, List<Subscriber>> subscribers = new HashMap<>();

    public void subscribe(String topic, Subscriber subscriber) {
        List<Subscriber> subscriberList = subscribers.get(topic);
        if (subscriberList == null) {
            subscriberList = new ArrayList<>();
            subscribers.put(topic, subscriberList);
        }
        subscriberList.add(subscriber);
    }

    public void unsubscribe(String topic, Subscriber subscriber) {
        List<Subscriber> subscriberList = subscribers.get(topic);
        if (subscriberList != null) {
            subscriberList.remove(subscriber);
        }
    }

    public void publish(String topic, String message) {
        List<Subscriber> subscriberList = subscribers.get(topic);
        if (subscriberList != null) {
            for (Subscriber subscriber : subscriberList) {
                subscriber.update(message);
            }
        }
    }
}

class EmailSubscriber implements Subscriber {
    private String email;

    public EmailSubscriber(String email) {
        this.email = email;
    }

    public void update(String message) {
        System.out.println("Send email to " + email + ": " + message);
    }
}

class SMSSubscriber implements Subscriber {
    private String phoneNumber;

    public SMSSubscriber(String phoneNumber) {
        this.phoneNumber = phoneNumber;
    }

    public void update(String message) {
        System.out.println("Send SMS to " + phoneNumber + ": " + message);
    }
}

public class Main {
    public static void main(String[] args) {
        Publisher publisher = new Publisher();

        Subscriber emailSubscriber1 = new EmailSubscriber("foo@example.com");
        Subscriber smsSubscriber1 = new SMSSubscriber("1234567890");

        publisher.subscribe("news", emailSubscriber1);
        publisher.subscribe("news", smsSubscriber1);

        publisher.publish("news", "发布新消息1");
        publisher.unsubscribe("news", smsSubscriber1);
        publisher.publish("news", "发布新消息2");
    }
}

Send email to foo@example.com: 发布新消息1
Send SMS to 1234567890: 发布新消息1
Send email to foo@example.com: 发布新消息2

public class OrderEvent extends ApplicationEvent {
  void onApplicationEvent(Object event) {
    ...
  }
}

@Component
public class OrderListener implements ApplicationListener<OrderEvent> {
    @Override
    public void onApplicationEvent(OrderEvent event) {
    // 生成订单、删除购物车、扣减库存
    ...
    }
}

@Resource
private ApplicationEventPublisher applicationEventPublisher;

private void saveOrder(MallUserVO mallUserVO, Long couponUserId, List<ShopCatVO> shopcatVOList, String orderNo) {
    // 订单检查
    ...
    // 生成订单号
    String orderNo = NumberUtil.genOrderNo();
    // 发布订单事件，在事件监听中处理下单逻辑
    applicationEventPublisher.publishEvent(new OrderEvent(orderNo, mallUserVO, couponUserId, shopcatVOList));
    // 所有操作成功后，将订单号返回
    return orderNo;
    ...
}

/**
 * 系统启动时執行
 */
@Component
public class SpringBeanStartupRunner implements ApplicationRunner {

    @Override
    public void run(ApplicationArguments args) throws Exception {
        // 设置spring默认的事件监听为异步执行
        SimpleApplicationEventMulticaster multicaster = SpringContextUtil.getBean(SimpleApplicationEventMulticaster.class);
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
                5,
                10,
                60L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<>(500),
                new CustomizableThreadFactory("newbee—event-task"),
                new ThreadPoolExecutor.CallerRunsPolicy()
        );
        multicaster.setTaskExecutor(threadPoolExecutor);
    }
}