RocketMQ入门（3）拉取消息

来源：互联网发布：淘宝代写毕业论文靠谱编辑：程序博客网时间：2024/04/28 14:41

转自：http://www.changeself.net/archives/rocketmq入门（3）拉取消息.html

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
*/
publicclassPullConsumer{
    //Java缓存
    privatestaticfinalMap<MessageQueue,Long>offseTable=newHashMap<MessageQueue,Long>();
    publicstaticvoidmain(String[]args)throwsMQClientException{
        DefaultMQPullConsumerconsumer=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(MessageQueuemq:mqs){
            System.out.println("Consume from the queue: "+mq);
            SINGLE_MQ:while(true){
                try{
                    
                    PullResultpullResult=
                            consumer.pullBlockIfNotFound(mq,null,getMessageQueueOffset(mq),32);
                    List<MessageExt>list=pullResult.getMsgFoundList();
                    if(list!=null&&list.size()<100){
                        for(MessageExtmsg: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(MessageQueuemq,longoffset){
        offseTable.put(mq,offset);
    }
    privatestaticlonggetMessageQueueOffset(MessageQueuemq){
        Longoffset=offseTable.get(mq);
        if(offset!=null){
            System.out.println(offset);
            returnoffset;
        }
        return0;
    }

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

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