RocketMQ入门(消费者)_3

消费者角色：

1. 推式（一般建议用推式）

2. 拉式

消费模式：

1. 集群(cluster)                --均衡负载消费

2. 广播（broadcasting） --发布和订阅者模式

MQ的消费不会清除broker中的数据，broker数据一直存在队列中，队列offset会一直递增，因此可以通过回查来获取到丢失数据。这个时候我们可以采用pull形式较好。

push形式，MQ会记录访问的偏移量，即使宕机下次重启也会按照顺序继续消费，不会出现重复消费。

在RocketMQ入门（生产者）_2中已经写过一个推式的代码，接下来就看下拉式。

/**
 * 普通拉式消费者，代码编写
 * @author DennyZhao
 *
 */
public class PullConsumer {

    /**
     * 暂时以map作为offset入库看待。<queueId， offset>
     */
    private static Map<String, Long> offsetMap = new HashMap<String, Long>();

    public static void main(String[] args) throws UnsupportedEncodingException {
        //创建拉式消费者
        DefaultMQPullConsumer pullConsumer = new DefaultMQPullConsumer("pullConsumerGroup");
        pullConsumer.setNamesrvAddr("192.168.68.137:9876;192.168.68.138:9876;");
        try {
            pullConsumer.start();
            Set<MessageQueue> mqSet= pullConsumer.fetchSubscribeMessageQueues("fruit");
            while(true) {
            //循环队列
            for(MessageQueue mq: mqSet) {
                // 从队列中获取固定偏移值
                PullResult pullResult = pullConsumer.pullBlockIfNotFound(mq, "*", getOffset(mq), 32);
                setOffset(mq, pullResult.getNextBeginOffset());
                switch(pullResult.getPullStatus()) {
                case FOUND:
                    List<MessageExt> msgFoundList = pullResult.getMsgFoundList();
                    for(MessageExt msg : msgFoundList) {
                        String fruit = new String(msg.getBody(), RemotingHelper.DEFAULT_CHARSET);
                        System.out.println(fruit + "   -----fruit");
                    }
                    break;
                case NO_NEW_MSG:
                    break;
                case NO_MATCHED_MSG:
                    break;
                }
            }
            Thread.sleep(2000);
            }
        } catch (MQClientException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (RemotingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (MQBrokerException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * set offset
     * @param mq
     * @param nextBeginOffset
     */
    private static void setOffset(MessageQueue mq, long nextBeginOffset) {
        String queueId = mq.getBrokerName() + mq.getTopic() + mq.getQueueId();
        offsetMap.put(queueId, nextBeginOffset);
    }

    /**
     * 获取固定偏移值
     * @param mq queueId
     * @return int
     */
    private static long getOffset(MessageQueue mq) {
        String queueId = mq.getBrokerName() + mq.getTopic() + mq.getQueueId();
        Long offset =  offsetMap.get(queueId);
        if(offset == null) {
            offset = 0l;
        }
        System.out.println(offset + "---------------");
        return offset;
    }

}

使用Schedule拉式：

/**
 * ScheduleService 進行數據拉取
 * @author DennyZhao
 *
 */
public class PullScheduleService {

    public static void main(String[] args) throws MQClientException {
        MQPullConsumerScheduleService scheduleService = new MQPullConsumerScheduleService("scheduleConsumers");
        scheduleService.setMessageModel(MessageModel.CLUSTERING);
        scheduleService.setPullThreadNums(4);
        DefaultMQPullConsumer defaultMQPullConsumer = new DefaultMQPullConsumer("pullConsumer");
        defaultMQPullConsumer.setNamesrvAddr("192.168.68.137:9876;192.168.68.138:9876;");
        scheduleService.setDefaultMQPullConsumer(defaultMQPullConsumer);
        scheduleService.registerPullTaskCallback("fruit", new PullTaskCallback() {
            /**
             * 数据处理
             */
            @Override
            public void doPullTask(MessageQueue mq, PullTaskContext context) {
                MQPullConsumer pullConsumer = context.getPullConsumer();
                try {
                    long offset = pullConsumer.fetchConsumeOffset(mq, false);
                    PullResult pull = pullConsumer.pull(mq, "*", offset, 32);
                    switch(pull.getPullStatus()) {
                    case FOUND:
                        // 结果输出
                        List<MessageExt> msgFoundList = pull.getMsgFoundList();
                        for(MessageExt msg : msgFoundList) {
                            String fruit = new String(msg.getBody(), RemotingHelper.DEFAULT_CHARSET);
                            System.out.println("result:   " + fruit);
                        }
                        break;
                    case NO_MATCHED_MSG:
                        break;
                    default:

                    }
                    // 获取下一个循环的offset
                    pullConsumer.updateConsumeOffset(mq, pull.getNextBeginOffset());
                    // 设置下次访问时间
                    context.setPullNextDelayTimeMillis(1000);
                } catch (MQClientException | RemotingException | MQBrokerException | InterruptedException | UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
            }
        });
        scheduleService.start();
    }

}

参数说明：

//push主要参数
DefaultMQPushConsumer pushConsumer = new DefaultMQPushConsumer("pushConsumerGroup");
// 从何地开始，默认（CONSUME_FROM_LAST_OFFSET）
pushConsumer.setConsumeFromWhere(ConsumeFromWhere.CONSUME_FROM_LAST_OFFSET);
pushConsumer.setConsumeThreadMin(2); //最小线程数
pushConsumer.setConsumeThreadMax(8); //最大线程数
pushConsumer.setConsumeTimeout(5000); //连接超时
pushConsumer.setMessageModel(MessageModel.CLUSTERING);//消息模式（集群CLUSTERING和广播BROADCASTING，default:cluster）
pushConsumer.setConsumeConcurrentlyMaxSpan(1000);//单队列最大消费数1000
pushConsumer.setConsumeMessageBatchMaxSize(1); //批量消费数1
pushConsumer.setNamesrvAddr("192.168.68.137:9876;192.168.68.138:9876;");//集群IP
pushConsumer.setHeartbeatBrokerInterval(2000); //心跳监测
pushConsumer.setMaxReconsumeTimes(3);//重复消费次数,用于失败后重试
pushConsumer.queryMessage(topic, key, maxNum, begin, end); //获取消息
pushConsumer.fetchSubscribeMessageQueues(topic);//订阅topic
pushConsumer.registerMessageListener(new MessageListenerConcurrently());//及时普通消费型
pushConsumer.registerMessageListener(new MessageListenerOrderly()); //严格顺序消费型;

        // pull常用参数
        //消息模式（集群CLUSTERING和广播BROADCASTING，default:cluster）
        pullConsumer.setMessageModel(MessageModel.CLUSTERING);
        pullConsumer.fetchSubscribeMessageQueues(topic);  //订阅主题
        pullConsumer.fetchConsumeOffset(mq, false);       //获取queue当前offset位置
        pullConsumer.pullBlockIfNotFound(mq, subExpression, offset, maxNums);//获取消费内容
        pullConsumer.updateConsumeOffset(mq, offset);  //更新消费位置
        pullConsumer.setConsumerPullTimeoutMillis(5000); //连接超时