RabbitMQ使用topic Exchange实现微服务分组订阅

        案例场景：用户下单后需要多个微服务（如营销、会员）分别订阅并处理订单事件，且每个微服务可能有多个集群实例，需要保证同一个微服务的集群中，只有一个实例消费到消息。

        不同于Kafka和rocketMQ有分组消费的功能，rabbitMQ需要通过topic Exchange实现。

        1、消息设计

{
  "event_type": "order_created",  // 事件类型（如下单、支付成功）
  "order_id": "123456",
  "user_id": "user_789",
  "items": [
    {"product_id": "p1001", "quantity": 2},
    {"product_id": "p1002", "quantity": 1}
  ],
  "total_amount": 399.00,
  "created_at": "2025-07-01T12:00:00Z"
}

        2、rabbitMQ设计

        使用 topic 类型的 Exchange：支持灵活的路由规则，不同微服务可通过 binding key 订阅特定事件。
        Exchange 名称示例：order_events。

微服务	    队列名	            绑定键（binding key）
营销系统	    marketing_queue	    order.created.marketing
会员系统	    member_queue	    order.created.member

绑定键规则：<event_type>.<microservice_name>，便于后续扩展（如 order.cancel.marketing）。

        3、消息发布

        生产者（订单服务）发布消息时，指定路由键（routing key） 为 order.created

import com.rabbitmq.client.Channel;
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;
import com.fasterxml.jackson.databind.ObjectMapper;

public class OrderProducer {
    private static final String EXCHANGE_NAME = "order_events";
    private static final String ROUTING_KEY = "order.created";

    public static void main(String[] args) throws Exception {
        // 1. 创建连接
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        factory.setUsername("guest");
        factory.setPassword("guest");

        try (Connection connection = factory.newConnection();
             Channel channel = connection.createChannel()) {

            // 2. topic Exchange
            channel.exchangeDeclare(EXCHANGE_NAME, "topic", true);

            // 3. 构造消息
            OrderEvent event = new OrderEvent();
            event.setEvent_type("order_created");
            event.setOrder_id("123456");
            event.setUser_id("user_789");
            event.setItems(List.of(Map.of("product_id", "p1001", "quantity", 2)));
            event.setTotal_amount(399.00);
            event.setCreated_at("2025-07-02T22:00:00Z");

            ObjectMapper mapper = new ObjectMapper();
            String messageJson = mapper.writeValueAsString(event);

            // 4. 发布消息
            channel.basicPublish(
                EXCHANGE_NAME,
                ROUTING_KEY,
                true, // 持久化消息
                new AMQP.BasicProperties.Builder()
                    .deliveryMode(2) // 持久化
                    .build(),
                messageJson.getBytes()
            );

            System.out.println("Sent order event: " + messageJson);
        }
    }
}

        4、消息订阅（营销服务）

        不同服务只需要修改 QUEUE_NAME 和 BINDING_KEY 就可以了。 

import com.rabbitmq.client.*;
import com.fasterxml.jackson.databind.ObjectMapper;

public class MarketingConsumer {
    private static final String QUEUE_NAME = "marketing_queue";
    private static final String BINDING_KEY = "order.created.marketing";

    public static void main(String[] args) throws Exception {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");
        factory.setUsername("guest");
        factory.setPassword("guest");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        // 1. 声明队列并绑定到 Exchange
        channel.queueDeclare(QUEUE_NAME, true, false, false, null);
        channel.queueBind(QUEUE_NAME, "order_events", BINDING_KEY);

        // 2. 消费者回调
        DeliverCallback deliverCallback = (consumerTag, delivery) -> {
            String messageJson = new String(delivery.getBody(), "UTF-8");
            ObjectMapper mapper = new ObjectMapper();
            OrderEvent event = mapper.readValue(messageJson, OrderEvent.class);

            // 3. 业务逻辑：发送营销短信
            System.out.println("Marketing: Sending SMS for order " + event.getOrder_id());

            // 4. 手动确认消息
            channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false);
        };

        // 5. 设置手动确认
        channel.basicConsume(QUEUE_NAME, false, deliverCallback, consumerTag -> {});
    }
}