RocketMQ入门（3）拉取消息

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RocketMQ入门（3）拉取消息

RocketMQ不止可以直接推送消息，在消费端注册监听器进行监听，还可以由消费端决定自己去拉取数据

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/** * PullConsumer，订阅消息 */ public class PullConsumer {     //Java缓存     private static final Map<MessageQueue, Long> offseTable = new HashMap<MessageQueue, Long>();     public static void main(String[] args) throws MQClientException {         DefaultMQPullConsumer consumer = new DefaultMQPullConsumer("PullConsumerGroup");         consumer.setNamesrvAddr("127.0.0.1:9876");         consumer.start();                 //拉取订阅主题的队列，默认队列大小是4         Set<MessageQueue> mqs = consumer.fetchSubscribeMessageQueues("TopicTestMapBody");         for (MessageQueue mq : mqs) {             System.out.println("Consume from the queue: " + mq);             SINGLE_MQ:while(true){                 try {                                          PullResult pullResult =                             consumer.pullBlockIfNotFound(mq, null, getMessageQueueOffset(mq), 32);                     List<MessageExt> list=pullResult.getMsgFoundList();                     if(list!=null&&list.size()<100){                         for(MessageExt msg:list){                             System.out.println(SerializableInterface.deserialize(msg.getBody()));                         }                     }                     System.out.println(pullResult.getNextBeginOffset());                     putMessageQueueOffset(mq, pullResult.getNextBeginOffset());                                          switch (pullResult.getPullStatus()) {                     case FOUND:                         // TODO                         break;                     case NO_MATCHED_MSG:                         break;                     case NO_NEW_MSG:                         break SINGLE_MQ;                     case OFFSET_ILLEGAL:                         break;                     default:                         break;                     }                 }                 catch (Exception e) {                     e.printStackTrace();                 }              }         }         consumer.shutdown();     }     private static void putMessageQueueOffset(MessageQueue mq, long offset) {         offseTable.put(mq, offset);     }     private static long getMessageQueueOffset(MessageQueue mq) {         Long offset = offseTable.get(mq);         if (offset != null){             System.out.println(offset);             return offset;         }         return 0;     }

刚开始的没有细看PullResult对象，以为拉取到的结果没有MessageExt对象还跑到群里面问别人，犯2了

特别要注意  静态变量offsetTable的作用，拉取的是按照从offset（理解为下标）位置开始拉取，拉取N条，offsetTable记录下次拉取的offset位置