RocketMQ中MessageExt属性

https://blog.csdn.net/shi_hong_fei_hei/article/details/115585793?utm_medium=distribute.pc_relevant.none-task-blog-2~default~baidujs_baidulandingword~default-0.topblog&spm=1001.2101.3001.4242.1&utm_relevant_index=3

https://blog.csdn.net/Nicholas___/article/details/108689772

这两篇比较全了。

还有一点是setMaxReconsumeTimes  这个参数

//在默认的消费者里 消费重试次数 -1代表16次，不是无限次数
 defaultMQPushConsumer.setMaxReconsumeTimes(-1);

public class DefaultMQPushConsumerImpl implements MQConsumerInner {

    //......

    public void sendMessageBack(MessageExt msg, int delayLevel, final String brokerName)
        throws RemotingException, MQBrokerException, InterruptedException, MQClientException {
        try {
            String brokerAddr = (null != brokerName) ? this.mQClientFactory.findBrokerAddressInPublish(brokerName)
                : RemotingHelper.parseSocketAddressAddr(msg.getStoreHost());
            this.mQClientFactory.getMQClientAPIImpl().consumerSendMessageBack(brokerAddr, msg,
                this.defaultMQPushConsumer.getConsumerGroup(), delayLevel, 5000, getMaxReconsumeTimes());
        } catch (Exception e) {
            log.error("sendMessageBack Exception, " + this.defaultMQPushConsumer.getConsumerGroup(), e);

            Message newMsg = new Message(MixAll.getRetryTopic(this.defaultMQPushConsumer.getConsumerGroup()), msg.getBody());

            String originMsgId = MessageAccessor.getOriginMessageId(msg);
            MessageAccessor.setOriginMessageId(newMsg, UtilAll.isBlank(originMsgId) ? msg.getMsgId() : originMsgId);

            newMsg.setFlag(msg.getFlag());
            MessageAccessor.setProperties(newMsg, msg.getProperties());
            MessageAccessor.putProperty(newMsg, MessageConst.PROPERTY_RETRY_TOPIC, msg.getTopic());
            MessageAccessor.setReconsumeTime(newMsg, String.valueOf(msg.getReconsumeTimes() + 1));
            MessageAccessor.setMaxReconsumeTimes(newMsg, String.valueOf(getMaxReconsumeTimes()));
            newMsg.setDelayTimeLevel(3 + msg.getReconsumeTimes());

            this.mQClientFactory.getDefaultMQProducer().send(newMsg);
        } finally {
            msg.setTopic(NamespaceUtil.withoutNamespace(msg.getTopic(), this.defaultMQPushConsumer.getNamespace()));
        }
    }

    private int getMaxReconsumeTimes() {
        // default reconsume times: 16
        if (this.defaultMQPushConsumer.getMaxReconsumeTimes() == -1) {
            return 16;
        } else {
            return this.defaultMQPushConsumer.getMaxReconsumeTimes();
        }
    }

    //......
}

默认消费者是无序消息 ，没有消费顺序的。