RocketMQ之Consumer整体介绍启动源码分析

// org.apache.rocketmq.client.consumer.MQConsumer
public interface MQConsumer extends MQAdmin {
    // 如果消费失败，消息将被发送回代理，并延迟消耗一些时间
    void sendMessageBack(final MessageExt msg/*消息*/, final int delayLevel/*延迟级别*/, final String brokerName);  
    // 根据topic从使用者缓存中获取消息队列
    Set<MessageQueue> fetchSubscribeMessageQueues(final String topic) throws MQClientException;
}
// org.apache.rocketmq.client.consumer.MQPushConsumer
public interface MQPushConsumer extends MQConsumer {
    // 启动Consumer
    void start() throws MQClientException;
    // 关闭Consumer
    void shutdown();
    // 注册并发消息Listener
    void registerMessageListener(final MessageListenerConcurrently messageListener);
    // 注册顺序消息Listener,将会有序地接收消息。一个队列一个线程
    void registerMessageListener(final MessageListenerOrderly messageListener);
    // 订阅Topic
    void subscribe(final String topic, final String subExpression) throws MQClientException;
    // 退订topic
    void unsubscribe(final String topic);
}

// org.apache.rocketmq.client.consumer.DefaultMQPushConsumer
public class DefaultMQPushConsumer extends ClientConfig implements MQPushConsumer {
    // DefaultMQPushConsumer的默认实现，DefaultMQPushConsumer中大部分功能都是对它的代理
    protected final transient DefaultMQPushConsumerImpl defaultMQPushConsumerImpl;
    // 相同角色的消费者需要具有完全相同的subscriptions和consumerGroup才能正确实现负载平衡，它需要全局唯一
    private String consumerGroup;
    // 消息模型定义了如何将消息传递到每个消费者客户端的方式，默认是集群模式
    private MessageModel messageModel = MessageModel.CLUSTERING;
  	// 第一次消费时指定的消费策略，默认是CONSUME_FROM_LAST_OFFSET
    private ConsumeFromWhere consumeFromWhere = ConsumeFromWhere.CONSUME_FROM_LAST_OFFSET;
  	// 队列分配算法，指定如何将消息队列分配给每个使用者客户端。
    private AllocateMessageQueueStrategy allocateMessageQueueStrategy;
    // 订阅关系
    private Map<String /* topic */, String /* sub expression */> subscription = new HashMap<String, String>();
    // 消息监听器
    private MessageListener messageListener;
    // 消息消费进度存储器
    private OffsetStore offsetStore;
  	// 最小消费线程数
    private int consumeThreadMin = 20;
    // 最大消费线程数
    private int consumeThreadMax = 20;
    // 推送模式下拉去消息的间隔时间，默认一次拉取消息完成后立刻继续拉取
    private long pullInterval = 0;
    // 批量消费数量
    private int consumeMessageBatchMaxSize = 1;
    // 批量拉取的数量
    private int pullBatchSize = 32;
  	// 每次拉取时是否更新订阅关系,默认是false
    private boolean postSubscriptionWhenPull = false;
    // 消息最大重试次数，如果消息消费最大次数超过maxReconsumeTimes还未成功，则消息将被转移到一个失败队列
    private int maxReconsumeTimes = -1;
    //延迟将该队列的消息提交到消费者线程的等待时间，默认延迟1s
    private long suspendCurrentQueueTimeMillis = 1000;
    // 消息阻塞消费线程的最大超时时间，默认15分钟
    private long consumeTimeout = 15;
    // 关闭使用者时等待消息的最长时间，0表示没有等待。
    private long awaitTerminationMillisWhenShutdown = 0;
}

public static void main(String[] args) throws MQClientException {
    // 1. 传入CONSUMER_GROUP，创建DefaultMQPushConsumer
    DefaultMQPushConsumer consumer = new DefaultMQPushConsumer(CONSUMER_GROUP);
  	// 2. 设置namesrvAddr
  	consumer.setNamesrvAddr("127.0.0.1:9876");
    // 3. 订阅Topic 
    consumer.subscribe(TOPIC, "*");
    // 4.注册消息Listener
    consumer.registerMessageListener((MessageListenerConcurrently) (msg, context) -> {
        System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msg);
        return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
    });
    // 5.启动Consumer
    consumer.start();
}

// org.apache.rocketmq.client.consumer.DefaultMQPushConsumer#start
public void start() throws MQClientException {
    // consumerGroup封装namespace
    setConsumerGroup(NamespaceUtil.wrapNamespace(this.getNamespace(), this.consumerGroup));
    // DefaultMQPushConsumerImpl启动
    this.defaultMQPushConsumerImpl.start();
    // 消息轨迹跟踪服务，默认null
    if (null != traceDispatcher) {
        try {
            traceDispatcher.start(this.getNamesrvAddr(), this.getAccessChannel());
        } catch (MQClientException e) {
            log.warn("trace dispatcher start failed ", e);
        }
    }
}

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start
public synchronized void start() throws MQClientException {
  //...
  // 状态先设置为启动失败
  this.serviceState = ServiceState.START_FAILED;
  // 校验配置，ConsumerGroup校验，
  this.checkConfig();
  // 订阅关系copy到RebalanceImpl中
  this.copySubscription();
  // 如果是集群模式，消费者名称如果是DEFAULT，则会改成：PID#时间戳
  if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
      this.defaultMQPushConsumer.changeInstanceNameToPID();
  }
  //...
}

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start
// 生成一个MQClientInstance
this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);
// 设置消费者组
this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
// 消息消费模式
this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
// 设置消息消费模式
this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
// 设置MQClientInstance
this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);
// 构建拉消息包装器
this.pullAPIWrapper = new PullAPIWrapper(
    mQClientFactory,
    this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start
if (this.defaultMQPushConsumer.getOffsetStore() != null) {
    this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
} else {
    switch (this.defaultMQPushConsumer.getMessageModel()) {
        case BROADCASTING:
            // 如果是广播模式，则使用LocalFileOffsetStore存储偏移量
            this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
            break;
        case CLUSTERING:
            // 如果是集群模式，则使用RemoteBrokerOffsetStore存储偏移量
            this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
            break;
        default:
            break;
    }
    this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);
}
// 如果是广播模式，则从本地文件load偏移量，如果是集群模式则是一个空实现
this.offsetStore.load();

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start
// 如果是顺序消费
if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
    this.consumeOrderly = true;
    this.consumeMessageService =
        new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
// 如果是并发消费
} else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
    this.consumeOrderly = false;
    this.consumeMessageService =
        new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
}
this.consumeMessageService.start();
// 将自身注册到MQClientInstance
boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
// ...
mQClientFactory.start();

// org.apache.rocketmq.client.impl.consumer.DefaultMQPushConsumerImpl#start
// 向Namesrv拉取并更新当前消费者订阅topic路由信息
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
// 随机选择一个Broker，发送检查客户端tag配置的请求，主要是检测Broker是否支持SQL92类型的tag过滤以及SQL92的tag语法是否正确
this.mQClientFactory.checkClientInBroker();
// 给所有Broker发送心跳
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
// 唤醒负载均衡服务rebalanceService，并进行rebalance
this.mQClientFactory.rebalanceImmediately();