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。
*/
private static Map offsetMap = new HashMap();
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 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 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 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