rocketmq tags

tags Tags As the
name suggests , tags are the tags of a message.
Generation method
Message msg = new Message("PullTopic", "pull", i+"", 1+"".getBytes());
Message msg = new Message();
msg.setTags("pull"); in the above code The pull is the label.
How to use it.
DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("PushConsumer");
consumer.setNamesrvAddr("127.0.0.1:9876");
//Subscribe to messages with the tag push under PushTopic
consumer.subscribe("PullTopic", "pull");
consumer.registerMessageListener (
    new MessageListenerConcurrently() {
        public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> list,

                        Message msg = list.get(0);       
                        return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
                    }
                }
            );
consumer.start(); wow! ! ! Isn't it great. Different MessageListenerConcurrently instances consume different messages. Can solve many problems.
Hehe, hehe
The truth about
tags is meaningless to Broker. Do not do any processing.
Consumer just filters messages based on tags.
The following is the core method of tags processing
public class DefaultMQPushConsumerImpl implements MQConsumerInner {

    public void subscribe(String topic, String subExpression) throws MQClientException {
        try {
            SubscriptionData subscriptionData =
                    FilterAPI.buildSubscriptionData(this.defaultMQPushConsumer.getConsumerGroup(),//
                        topic, subExpression);
            this.rebalanceImpl.getSubscriptionInner().put(topic, subscriptionData);
            if (this.mQClientFactory != null) {
                this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
            }
        }
        catch (Exception e) {
            throw new MQClientException("subscription exception", e);
        }
    }
   
    public void subscribe(String topic, String fullClassName, String filterClassSource)
        throws MQClientException {
        try {
            SubscriptionData subscriptionData =
                    FilterAPI.buildSubscriptionData(this.defaultMQPushConsumer.getConsumerGroup(),//
                        topic, "*");
            subscriptionData.setSubString(fullClassName);
            subscriptionData.setClassFilterMode(true);
            subscriptionData.setFilterClassSource(filterClassSource);
            this.rebalanceImpl.getSubscriptionInner().put(topic, subscriptionData);
            if (this.mQClientFactory != null) {
                this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
            }
       
        }
        catch (Exception e) {
            throw new MQClientException("subscription exception", e);
        }
    }
}消息过滤的方法
public class PullAPIWrapper {
   
    public PullResult processPullResult(final MessageQueue mq, final PullResult pullResult,
            final SubscriptionData subscriptionData) {
        PullResultExt pullResultExt = (PullResultExt) pullResult;

        this.updatePullFromWhichNode(mq, pullResultExt.getSuggestWhichBrokerId());
        if (PullStatus.FOUND == pullResult.getPullStatus()) {
            ByteBuffer byteBuffer = ByteBuffer.wrap(pullResultExt.getMessageBinary());
            List<MessageExt> msgList = MessageDecoder.decodes(byteBuffer);

            List<MessageExt> msgListFilterAgain = msgList;
            if (!subscriptionData.getTagsSet().isEmpty() && !subscriptionData.isClassFilterMode()) {
                msgListFilterAgain = new ArrayList<MessageExt>(msgList.size());
                for (MessageExt msg : msgList) {
                    if (msg.getTags() != null) {
                        if (subscriptionData.getTagsSet().contains(msg.getTags())) {
                            msgListFilterAgain.add(msg);
                        }
                    }
                }
            }

            if (this.hasHook()) {
                FilterMessageContext filterMessageContext = new FilterMessageContext();
                filterMessageContext.setUnitMode(unitMode);
                filterMessageContext.setMsgList(msgListFilterAgain);
                this.executeHook(filterMessageContext);
            }

            for (MessageExt msg : msgListFilterAgain) {
                MessageAccessor.putProperty(msg, MessageConst.PROPERTY_MIN_OFFSET,
                    Long.toString(pullResult.getMinOffset()));
                MessageAccessor.putProperty(msg, MessageConst.PROPERTY_MAX_OFFSET,
                    Long.toString(pullResult.getMaxOffset()));
            }

            pullResultExt.setMsgFoundList(msgListFilterAgain);
        }

        pullResultExt.setMessageBinary(null);

        return pullResult;
    }
}

//processPullResult 会被 pull操作成功之后调用
public class DefaultMQPullConsumerImpl implements MQConsumerInner {
    private void pullAsyncImpl(//
                               final MessageQueue mq,//
                               final String subExpression,//
                               final long offset,//
                               final int maxNums,//
                               final PullCallback pullCallback,//
                               final boolean block,//
                               final long timeout) throws MQClientException, RemotingException, InterruptedException {
    .......
    this.pullAPIWrapper.pullKernelImpl(//
                    mq, // 1
                    subscriptionData.getSubString(), // 2
                    0L, // 3
                    offset, // 4
                    maxNums, // 5
                    sysFlag, // 6
                    0, // 7
                    this.defaultMQPullConsumer.getBrokerSuspendMaxTimeMillis(), // 8
                    timeoutMillis, // 9
                    CommunicationMode.ASYNC, // 10
                    new PullCallback() {

                        @Override
                        public void onException(Throwable e) {
                            pullCallback.onException(e);
                        }


                        @Override
                        public void onSuccess(PullResult pullResult) {
                            pullCallback.onSuccess(DefaultMQPullConsumerImpl.this.pullAPIWrapper
                                    .processPullResult(mq, pullResult, subscriptionData));
                        }
                    });
                              
    }
   
    public void pullMessage(final PullRequest pullRequest) {
        ..........
         PullCallback pullCallback = new PullCallback() {
            @Override
            public void onSuccess(PullResult pullResult) {
                if (pullResult != null) {
                    pullResult =DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(
                                pullRequest.getMessageQueue(), pullResult, subscriptionData);
        ........
    }

    private PullResult pullSyncImpl(MessageQueue mq, String subExpression, long offset, int maxNums,
                                boolean block, long timeout) throws MQClientException, RemotingException, MQBrokerException,
        InterruptedException {
    this.makeSureStateOK();

    if (null == mq) {
        throw new MQClientException("mq is null", null);

    }

    if (offset < 0) {
        throw new MQClientException("offset < 0", null);
    }

    if (maxNums <= 0) {
        throw new MQClientException("maxNums <= 0", null);
    }

    this.subscriptionAutomatically(mq.getTopic());

    int sysFlag = PullSysFlag.buildSysFlag(false, block, true, false);

    SubscriptionData subscriptionData;
    try {
        subscriptionData = FilterAPI.buildSubscriptionData(this.defaultMQPullConsumer.getConsumerGroup(),//
                mq.getTopic(), subExpression);
    } catch (Exception e) {
        throw new MQClientException("parse subscription error", e);
    }

    long timeoutMillis =
            block ? this.defaultMQPullConsumer.getConsumerTimeoutMillisWhenSuspend() : timeout;

    PullResult pullResult = this.pullAPIWrapper.pullKernelImpl(//
            mq, // 1
            subscriptionData.getSubString(), // 2
            0L, // 3
            offset, // 4
            maxNums, // 5
            sysFlag, // 6
            0, // 7
            this.defaultMQPullConsumer.getBrokerSuspendMaxTimeMillis(), // 8
            timeoutMillis, // 9
            CommunicationMode.SYNC, // 10
            null// 11
    );

    return this.pullAPIWrapper.processPullResult(mq, pullResult, subscriptionData);
} So the role of tags is to filter messages in the Consumer.
For example, all orders are pushed to a topic, and there are N services for consumption, and each service only corresponds to a merchant on one platform. Similar scenarios can use tags
DefaultMQPullConsumer There is no subscribe method, so message filtering needs to be done by yourself. very good.