public class DefaultMQPushConsumerSample {
    public static void main(String[] args) throws MQClientException {
        // Consumer 的 GroupName 用于把多个 Consumer 组织到一起，提高并发处理能力，GroupName 需要和消息模式（ MessageModel） 配合使用。
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name");
        // NameServer 的地址和端口号，可以填写多个，用分号隔开，达到消除单点故障的目的，比如“ip1：port；ip2：port；ip3：port”。
        consumer.setNamesrvAddr("127.0.0.1:9876");
        /* Specify where to start in case the specified Consumer group is a brand new one. */
        consumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_FIRST_OFFSET);
        consumer.setMessageModel(MessageModel.BROADCASTING);
        /* Subscribe one more more Topics to consume. */
        // Topic 名称用来标识消息类型，需要提前创建。
        // 如果不需要消费某个 Topic 下的所有消息，可以通过指定消息的 Tag 进行消息过滤，
        // 比如：Consumer.subscribe（"TopicTest"，"tag1||tag2||tag3"），表示这个 Consumer 要消费“TopicTest”下带有tag1或tag2或tag3的消息
        // （ Tag 是在发送消息时设置的标签）。在填写 Tag 参数的位置， 用 null 或者“*” 表示要消费这个 Topic 的所有消息。
        consumer.subscribe("TopicTest", "*");
        /* * Register callback to execute on arrival of Messages fetched from brokers. */
        consumer.registerMessageListener(
                (MessageListenerConcurrently) (msgs, context) -> {
                    System.out.printf(Thread.currentThread().getName() + " Receive New Messages: " + msgs + "%n");
                    System.out.println();
                    return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
                });
        /* * Launch the Consumer instance.*/
        consumer.start();
    }
}

PullCallback pullCallback = new PullCallback() {
    public void onSuccess(PullResult pullResult) {
        if (pullResult != null) {
            pullResult = DefaultMQPushConsumerImpl.this.pullAPIWrapper.processPullResult(pullRequest.getMessageQueue(), pullResult, subscriptionData);
            switch(pullResult.getPullStatus()) {
            case FOUND:
              // 省略代码
                break;
            case NO_NEW_MSG:
              // 省略代码
                break;
            case NO_MATCHED_MSG:
              // 省略代码
                break;
            case OFFSET_ILLEGAL:
                // 省略代码
            }
        }
    }
    public void onException(Throwable e) {
        if (!pullRequest.getMessageQueue().getTopic().startsWith("%RETRY%")) {
            DefaultMQPushConsumerImpl.this.log.warn("execute the pull request exception", e);
        }
        DefaultMQPushConsumerImpl.this.executePullRequestLater(pullRequest, 3000L);
    }
};

PullMessageRequestHeader requestHeader = new PullMessageRequestHeader();
requestHeader.setConsumerGroup(this.consumerGroup);
requestHeader.setTopic(mq.getTopic());
requestHeader.setQueueId(mq.getQueueId());
requestHeader.setQueueOffset(offset);
requestHeader.setMaxMsgNums(maxNums);
requestHeader.setSysFlag(sysFlagInner);
requestHeader.setCommitOffset(commitOffset);
requestHeader.setSuspendTimeoutMillis(brokerSuspendMaxTimeMillis);
requestHeader.setSubscription(subExpression);
requestHeader.setSubVersion(subVersion);
String brokerAddr = findBrokerResult.getBrokerAddr();
if (PullSysFlag.hasClassFilterFlag(sysFlagInner)) {
    brokerAddr = this.computPullFromWhichFilterServer(mq.getTopic(), brokerAddr);
}
PullResult pullResult = this.mQClientFactory.getMQClientAPIImpl().
  pullMessage(brokerAddr, requestHeader, timeoutMillis, communicationMode, pullCallback);

if (this.brokerController.getBrokerConfig().isLongPollingEnable()){
    this.waitForRunning( 5 * 1000); 
} else {
  this.waitForRunning(this.brokerController.getBrokerConfig().getShortPollingTimeMills()); 
}
long beginLockTimestamp = this.systemClock.now(); 
this.checkHoldRequest(); 
long costTime = this.systemClock.now() - beginLockTimestamp; 
if (costTime > 5 * 1000) { 
    Log. info("[ NOTIFYME] check hold request cost {} ms.", costTime); 
}

long size = processQueue.getMsgCount().get();
if (size > (long)this.defaultMQPushConsumer.getPullThresholdForQueue()) {
    this.executePullRequestLater(pullRequest, 50L);
    if (this.flowControlTimes1++ % 1000L == 0L) {
        this.log.warn("the consumer message buffer is full, so do flow control, minOffset={}, maxOffset={}, size={}, pullRequest={}, flowControlTimes={}", new Object[]{processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), size, pullRequest, this.flowControlTimes1});
    }
}

if (!this.consumeOrderly) {
        if (processQueue.getMaxSpan() > (long)this.defaultMQPushConsumer.getConsumeConcurrentlyMaxSpan()) {
            this.executePullRequestLater(pullRequest, 50L);
            if (this.flowControlTimes2++ % 1000L == 0L) {
                this.log.warn("the queue's messages, span too long, so do flow control, minOffset={}, maxOffset={}, maxSpan={}, pullRequest={}, flowControlTimes={}", new Object[]{processQueue.getMsgTreeMap().firstKey(), processQueue.getMsgTreeMap().lastKey(), processQueue.getMaxSpan(), pullRequest, this.flowControlTimes2});
            }
            return;
        }
    }

else {
        if (!processQueue.isLocked()) {
            this.executePullRequestLater(pullRequest, 3000L);
            this.log.info("pull message later because not locked in broker, {}", pullRequest);
            return;
        }
        if (!pullRequest.isLockedFirst()) {
            long offset = this.rebalanceImpl.computePullFromWhere(pullRequest.getMessageQueue());
            boolean brokerBusy = offset < pullRequest.getNextOffset();
            this.log.info("the first time to pull message, so fix offset from broker. pullRequest: {} NewOffset: {} brokerBusy: {}", new Object[]{pullRequest, offset, brokerBusy});
            if (brokerBusy) {
                this.log.info("[NOTIFYME]the first time to pull message, but pull request offset larger than broker consume offset. pullRequest: {} NewOffset: {}", pullRequest, offset);
            }
            pullRequest.setLockedFirst(true);
            pullRequest.setNextOffset(offset);
        }
    }