摘要： 源代码版本是3.2.6。在rocketmq里，consumer被分为2类：MQPullConsumer和MQPushConsumer，其实本质都是拉模式（pull），即consumer轮询从broker拉取消息。
源代码版本是3.2.6。在rocketmq里，consumer被分为2类：MQPullConsumer和MQPushConsumer，其实本质都是拉模式（pull），即consumer轮询从broker拉取消息。
区别是：
push方式里，consumer把轮询过程封装了，并注册MessageListener监听器，取到消息后，唤醒MessageListener的consumeMessage()来消费，对用户而言，感觉消息是被推送过来的。
pull方式里，取消息的过程需要用户自己写，首先通过打算消费的Topic拿到MessageQueue的集合，遍历MessageQueue集合，然后针对每个MessageQueue批量取消息，一次取完后，记录该队列下一次要取的开始offset，直到取完了，再换另一个MessageQueue。
文字描述可能不是很清楚，前面的文章都是push方式的，所以这里只上pull方式的，贴代码：
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<logback.version>1.0.13</logback.version>
<rocketmq.version>3.2.6</rocketmq.version>
</properties>
<dependencies>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.0.13</version>
</dependency>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-core</artifactId>
<version>1.0.13</version>
</dependency>
<dependency>
<groupId>com.alibaba.rocketmq</groupId>
<artifactId>rocketmq-client</artifactId>
<version>${rocketmq.version}</version>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.10</version>
<scope>test</scope>
</dependency>
</dependencies>
Producer：
package com.zoo.quickstart;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.client.producer.DefaultMQProducer;
import com.alibaba.rocketmq.client.producer.SendResult;
import com.alibaba.rocketmq.common.message.Message;
/**
* Producer，发送消息
*
*/
public class Producer {
public static void main(String[] args) throws MQClientException, InterruptedException {
DefaultMQProducer producer = new DefaultMQProducer("please_rename_unique_group_name");
producer.setNamesrvAddr("192.168.0.104:9876");
producer.start();
for (int i = 0; i < 5; i++) {
try {
Message msg = new Message("TopicTest",// topic
"TagA",// tag
("Hello RocketMQ " + i).getBytes()// body
);
SendResult sendResult = producer.send(msg);
System.out.println(sendResult);
Thread.sleep(6000);
}
catch (Exception e) {
e.printStackTrace();
Thread.sleep(3000);
}
}
producer.shutdown();
}
}
Consumer:
package com.zoo.quickstart.pull;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import com.alibaba.rocketmq.client.consumer.DefaultMQPullConsumer;
import com.alibaba.rocketmq.client.consumer.PullResult;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.common.message.MessageQueue;
/**
* PullConsumer，订阅消息
*/
public class PullConsumer {
private static final Map<MessageQueue, Long> offseTable = new HashMap<MessageQueue, Long>();
public static void main(String[] args) throws MQClientException {
DefaultMQPullConsumer consumer = new DefaultMQPullConsumer("please_rename_unique_group_name_5");
consumer.setNamesrvAddr("192.168.0.104:9876");
consumer.start();
Set<MessageQueue> mqs = consumer.fetchSubscribeMessageQueues("TopicTest");
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);
System.out.println(pullResult);
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)
return offset;
return 0;
}
}
还有一种定时的Consumer：
package com.zoo.quickstart.pull;
import com.alibaba.rocketmq.client.consumer.MQPullConsumer;
import com.alibaba.rocketmq.client.consumer.MQPullConsumerScheduleService;
import com.alibaba.rocketmq.client.consumer.PullResult;
import com.alibaba.rocketmq.client.consumer.PullTaskCallback;
import com.alibaba.rocketmq.client.consumer.PullTaskContext;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.common.message.MessageQueue;
import com.alibaba.rocketmq.common.protocol.heartbeat.MessageModel;
public class PullScheduleService {
public static void main(String[] args) throws MQClientException {
final MQPullConsumerScheduleService scheduleService = new MQPullConsumerScheduleService("GroupName1");
scheduleService.getDefaultMQPullConsumer().setNamesrvAddr("192.168.0.104:9876");
scheduleService.setMessageModel(MessageModel.CLUSTERING);
scheduleService.registerPullTaskCallback("TopicTest", new PullTaskCallback() {
@Override
public void doPullTask(MessageQueue mq, PullTaskContext context) {
MQPullConsumer consumer = context.getPullConsumer();
try {
// 获取从哪里拉取
long offset = consumer.fetchConsumeOffset(mq, false);
if (offset < 0)
offset = 0;
PullResult pullResult = consumer.pull(mq, "*", offset, 32);
System.out.println(offset + "\t" + mq + "\t" + pullResult);
switch (pullResult.getPullStatus()) {
case FOUND:
break;
case NO_MATCHED_MSG:
break;
case NO_NEW_MSG:
case OFFSET_ILLEGAL:
break;
default:
break;
}
// 存储Offset，客户端每隔5s会定时刷新到Broker
consumer.updateConsumeOffset(mq, pullResult.getNextBeginOffset());
// 设置再过100ms后重新拉取
context.setPullNextDelayTimeMillis(100);
}
catch (Exception e) {
e.printStackTrace();
}
}
});
scheduleService.start();
}
}
