RocketMq学习之消息发送

内容选自《Rocketmq技术内幕》，融入自己的思考见解以及其他优秀内容的解释说明

开局没有图，内容全靠编。

首先说到消息发送，我们就要思考以下问题：

消息的数据结构，消息的发送方式，生产者怎么启动的，消息发送的过程（如何保证高可用，一致性）

 

1.消息的发送方式

同步，异步，单向

public class SyncProducer {
  public static void main(String[] args) throws Exception {
    // Instantiate with a producer group name
    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
    // Specify name server addresses
    producer.setNamesrvAddr("localhost:9876");
    // Launch the producer instance
    producer.start();
    for (int i = 0; i < 100; i++) {
      // Create a message instance with specifying topic, tag and message body
      Message msg = new Message("TopicTest" /* Topic */,
        "TagA" /* Tag */,
        ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) /* Message body */
        );
      // Send message to one of brokers
      SendResult sendResult = producer.send(msg);
      // Check whether the message has been delivered by the callback of sendResult
      System.out.printf("%s%n", sendResult);
    }
    // Shut down once the producer instance is not longer in use
    producer.shutdown();
  }
}

public class AsyncProducer {
  public static void main(String[] args) throws Exception {
    // Instantiate with a producer group name
    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
    // Specify name server addresses
    producer.setNamesrvAddr("localhost:9876");
    // Launch the producer instance
    producer.start();
    producer.setRetryTimesWhenSendAsyncFailed(0);
    for (int i = 0; i < 100; i++) {
      final int index = i;
      // Create a message instance with specifying topic, tag and message body
      Message msg = new Message("TopicTest",
        "TagA",
        "OrderID188",
        "Hello world".getBytes(RemotingHelper.DEFAULT_CHARSET));
      // SendCallback: receive the callback of the asynchronous return result.
      producer.send(msg, new SendCallback() {
        @Override
        public void onSuccess(SendResult sendResult) {
          System.out.printf("%-10d OK %s %n", index,
            sendResult.getMsgId());
        }
        @Override
        public void onException(Throwable e) {
          System.out.printf("%-10d Exception %s %n", index, e);
          e.printStackTrace();
        }
      });
    }
    // Shut down once the producer instance is not longer in use
    producer.shutdown();
  }
}

 

public class OnewayProducer {
  public static void main(String[] args) throws Exception{
    // Instantiate with a producer group name
    DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
    // Specify name server addresses
    producer.setNamesrvAddr("localhost:9876");
    // Launch the producer instance
    producer.start();
    for (int i = 0; i < 100; i++) {
      // Create a message instance with specifying topic, tag and message body
      Message msg = new Message("TopicTest" /* Topic */,
        "TagA" /* Tag */,
        ("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET) /* Message body */
      );
      // Send in one-way mode, no return result
      producer.sendOneway(msg);
    }
    // Shut down once the producer instance is not longer in use
     producer.shutdown();
  }
}

 

public class Consumer {
  public static void main(String[] args) throws InterruptedException, MQClientException {
    // Instantiate with specified consumer group name
    DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("please_rename_unique_group_name");
    
    // Specify name server addresses
    consumer.setNamesrvAddr("localhost:9876");

    // Subscribe one or more topics and tags for finding those messages need to be consumed
    consumer.subscribe("TopicTest", "*");
    // Register callback to execute on arrival of messages fetched from brokers
    consumer.registerMessageListener(new MessageListenerConcurrently() {
      @Override
      public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
        System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
        // Mark the message that have been consumed successfully
        return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
      }
    });
    // Launch the consumer instance
    consumer.start();
    System.out.printf("Consumer Started.%n");
  }
}

官网demo，拿来直接用

2.消息的数据结构

 

/**
 * message全局构造函数
 * @param topic 主题
 * @param tags 子主题
 * @param keys message索引键，多个用空格隔开
 * @param flag 消息标志
 * @param body 消息体
 * @param waitStoreMsgOK 消息发送时是否等消息存储完再返回
 * 还有个delaymeLevel：消息延迟级别，用于定时消息和消息重试
 */
public Message(String topic, String tags, String keys, int flag, byte[] body, boolean waitStoreMsgOK) {
    this.topic = topic;
    this.flag = flag;
    this.body = body;

    if (tags != null && tags.length() > 0)
        this.setTags(tags);

    if (keys != null && keys.length() > 0)
        this.setKeys(keys);

    this.setWaitStoreMsgOK(waitStoreMsgOK);
}

3.消息生产者的启动流程

面试扯淡几步走：

①检查生产者是否符合要求，如果符合，改变生产者实例的进程id，目的是为了避免不同进程之间相同影响。

保证同一个jvm中的不同消费者和生产者获得的mqClientInstance是同一个。

②注册生产者组，创建mqClientInstance实例，全局唯一。并且将当前的生产者加入到mqClientInstance管理中。换句话就是创建一个生产者组，然后每启动一个生产者实例就往组里进行注册。

③启动mqClientInstance实例。

  public void start(final boolean startFactory) throws MQClientException {
        switch (this.serviceState) {
            case CREATE_JUST:
                this.serviceState = ServiceState.START_FAILED;

                this.checkConfig();
                //检查producerGroup是否符合要求，如果符合，改变生产者实例的进程id
                if (!this.defaultMQProducer.getProducerGroup().equals(MixAll.CLIENT_INNER_PRODUCER_GROUP)) {
                    this.defaultMQProducer.changeInstanceNameToPID();
                }

                this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQProducer, rpcHook);
                //注册生产者组
                boolean registerOK = mQClientFactory.registerProducer(this.defaultMQProducer.getProducerGroup(), this);
                if (!registerOK) {
                    this.serviceState = ServiceState.CREATE_JUST;
                    throw new MQClientException("The producer group[" + this.defaultMQProducer.getProducerGroup()
                        + "] has been created before, specify another name please.&#