RocketMQ（03）——通过Tag对消息分类

通过Tag对消息分类

RocketMQ建议一个业务系统只使用一个Topic，不同类型的消息通过tag来区分。tag可以在构造Message的时候指定，下面代码就指定了发送的消息的tag都为tag0。

@Test
public void sendWithTag() throws Exception {
  DefaultMQProducer producer = new DefaultMQProducer("group1");
  producer.setNamesrvAddr(nameServer);
  producer.start();
  for (int i = 0; i < 10; i++) {
    Message message = new Message("topic1", "tag0", ("hello with tag---" + i).getBytes());
    SendResult sendResult = producer.send(message);
    if (sendResult.getSendStatus() == SendStatus.SEND_OK) {
      System.out.println("消息发送成功：" + sendResult);
    } else {
      System.out.println("消息发送失败：" + sendResult);
    }
  }
  producer.shutdown();
}

也可以通过Message的setTags()进行指定。

@Test
public void sendWithTag() throws Exception {
  DefaultMQProducer producer = new DefaultMQProducer("group1");
  producer.setNamesrvAddr(nameServer);
  producer.start();
  for (int i = 0; i < 10; i++) {
    Message message = new Message("topic1", ("hello with tag---" + i).getBytes());
    message.setTags("tag0");
    SendResult sendResult = producer.send(message);
    if (sendResult.getSendStatus() == SendStatus.SEND_OK) {
      System.out.println("消息发送成功：" + sendResult);
    } else {
      System.out.println("消息发送失败：" + sendResult);
    }
  }
  producer.shutdown();
}

虽然参数名叫tags，但是一条消息只能指定一个tag。消费者进行消费的时候也可以指定需要消费的消息对应的tag，比如下面就指定了需要消费的消息对应的Topic是topic1，Tag是tag0。

@Test
public void testConsumeByTag() throws Exception {
  DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer_group2");
  consumer.setNamesrvAddr(nameServer);
  consumer.subscribe("topic1", "tag0");
  consumer.registerMessageListener(new MessageListenerConcurrently() {
    @Override
    public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
      System.out.println(Thread.currentThread().getName() + "收到了消息，数量是：" + msgs.size());
      AtomicInteger counter = new AtomicInteger();
      msgs.forEach(msg -> System.out.println(counter.incrementAndGet() + ".消息内容是：" + new String(msg.getBody())));
      return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
    }
  });
  consumer.start();
  TimeUnit.SECONDS.sleep(120);
}

同一消费者也可以同时订阅同一个Topic的多个Tag，多个Tag之间通过||进行分隔。比如下面代码就同时订阅了tag0、tag1和tag2。

@Test
public void testConsumeByTag() throws Exception {
  DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer_group2");
  consumer.setNamesrvAddr(nameServer);
  consumer.subscribe("topic1", "tag0||tag1||tag2");
  consumer.registerMessageListener(new MessageListenerConcurrently() {
    @Override
    public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
      System.out.println(Thread.currentThread().getName() + "收到了消息，数量是：" + msgs.size());
      AtomicInteger counter = new AtomicInteger();
      msgs.forEach(msg -> System.out.println(counter.incrementAndGet() + ".消息内容是：" + new String(msg.getBody())));
      return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
    }
  });
  consumer.start();
  TimeUnit.SECONDS.sleep(120);
}

（注：本文基于RocketMQ4.5.0所写）