RocketMQ入门（3）拉取消息

最新推荐文章于 2023-12-12 03:57:15 发布

wbj0110

最新推荐文章于 2023-12-12 03:57:15 发布

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分类专栏： RocketMQ 文章标签： RocketMQ

本文链接：https://blog.youkuaiyun.com/wbj0110/article/details/84605872

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本文详细介绍RocketMQ中PullConsumer的使用方式，包括初始化配置、拉取消息队列及处理流程。通过具体代码示例解释如何实现消息拉取，并解析PullResult对象，深入探讨offsetTable在消息拉取中的作用。

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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
 */

publicclassPullConsumer{

    //Java缓存

    privatestaticfinalMap<MessageQueue,Long>offseTable=newHashMap<MessageQueue,Long>();
 
 

    publicstaticvoidmain(String[]args)throwsMQClientException{

        DefaultMQPullConsumer consumer=newDefaultMQPullConsumer("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()){

                    caseFOUND:

                        // TODO

                        break;

                    caseNO_MATCHED_MSG:

                        break;

                    caseNO_NEW_MSG:

                        breakSINGLE_MQ;

                    caseOFFSET_ILLEGAL:

                        break;

                    default:

                        break;

                    }

                }

                catch(Exceptione){

                    e.printStackTrace();

                }

             }

        }
 

        consumer.shutdown();

    }
 
 

    privatestaticvoidputMessageQueueOffset(MessageQueue mq,longoffset){

        offseTable.put(mq,offset);

    }
 
 

    privatestaticlonggetMessageQueueOffset(MessageQueue mq){

        Longoffset=offseTable.get(mq);

        if(offset!=null){

            System.out.println(offset);

            returnoffset;

        }

        return0;

    }