观察者模式在Java微服务间的使用

一.、使用RabbitMQ来实现

(1) 生产者（订单微服务）

import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.stereotype.Service;

@Service
public class OrderService {
    private final RabbitTemplate rabbitTemplate;

    public OrderService(RabbitTemplate rabbitTemplate) {
        this.rabbitTemplate = rabbitTemplate;
    }

    public void createOrder(Long orderId) {
        // 创建订单逻辑
        System.out.println("订单创建成功: " + orderId);

        // 发送消息到 RabbitMQ
        rabbitTemplate.convertAndSend("order.exchange", "order.created", orderId);
    }
}

(2) 消费者（通知微服务）

import org.springframework.amqp.rabbit.annotation.RabbitListener;
import org.springframework.stereotype.Component;

@Component
public class NotificationService {

    @RabbitListener(queues = "order.queue")
    public void handleOrderCreated(Long orderId) {
        System.out.println("【通知服务】订单 " + orderId + " 创建成功，发送通知！");
    }
}

(3) 配置 RabbitMQ 交换机和队列

import org.springframework.amqp.core.*;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class RabbitMQConfig {

    @Bean
    public DirectExchange orderExchange() {
        return new DirectExchange("order.exchange");
    }

    @Bean
    public Queue orderQueue() {
        return new Queue("order.queue");
    }

    @Bean
    public Binding binding(Queue orderQueue, DirectExchange orderExchange) {
        return BindingBuilder.bind(orderQueue).to(orderExchange).with("order.created");
    }
}

二. 使用 Spring Cloud Stream

Spring Cloud Stream 结合 Kafka 或 RabbitMQ，可以简化微服务间的事件驱动架构。

(1) 生产者

import org.springframework.cloud.stream.function.StreamBridge;
import org.springframework.stereotype.Service;

@Service
public class OrderService {
    private final StreamBridge streamBridge;

    public OrderService(StreamBridge streamBridge) {
        this.streamBridge = streamBridge;
    }

    public void createOrder(Long orderId) {
        System.out.println("订单创建成功: " + orderId);

        // 发送事件
        streamBridge.send("orderCreated-out-0", orderId);
    }
}

(2) 消费者

import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Service;
import java.util.function.Consumer;

@Service
public class NotificationService {

    @Bean
    public Consumer<Long> orderCreated() {
        return orderId -> System.out.println("【通知服务】订单 " + orderId + " 创建成功，发送通知！");
    }
}

(3) 配置 application.yml

spring:
  cloud:
    stream:
      bindings:
        orderCreated-out-0:
          destination: order-events
        orderCreated-in-0:
          destination: order-events
      defaultBinder: rabbit