rocketmq(三 java操作rocket API, rocketmq 幂等性)

• JAVA操作rocketmq：

1.导入rocketmq所需要的依赖：

    <dependency>
            <groupId>com.alibaba.rocketmq</groupId>
            <artifactId>rocketmq-client</artifactId>
            <version>3.0.10</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba.rocketmq</groupId>
            <artifactId>rocketmq-all</artifactId>
            <version>3.0.10</version>
            <type>pom</type>
        </dependency>

2.创建生产者

package com.example.producer;

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;

public class Producer {
    public static void main(String[] args) throws MQClientException {
        DefaultMQProducer producer = new DefaultMQProducer("producer-group");
        producer.setNamesrvAddr("192.168.31.165:9876;192.168.31.144:9876");
        producer.setInstanceName("producer");
        producer.start();
        try {
            for (int i = 0; i < 10; i++) {
                // Thread.sleep(1000); // 每秒发送一次MQ
                Message msg = new Message("producer-topic", // topic 主题名称
                        "msg", // pull 临时值 在消费者消费的时候 可以根据msg类型进行消费
                        ("pushmsg-" + i).getBytes()// body 内容
                );
                SendResult sendResult = producer.send(msg);
                System.out.println(sendResult.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        producer.shutdown();
    }

}

3.创建消费者

package com.example.consumer;

import java.util.List;

import com.alibaba.rocketmq.client.consumer.DefaultMQPushConsumer;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
import com.alibaba.rocketmq.client.consumer.listener.MessageListenerConcurrently;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.common.message.MessageExt;

public class Consumer {
    public static void main(String[] args) throws MQClientException {
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer-group");

        consumer.setNamesrvAddr("192.168.31.165:9876;192.168.31.144:9876");
        consumer.setInstanceName("consumer");
        consumer.subscribe("producer-topic", "msg");//此处是根据Message对象的参数来获取

        consumer.registerMessageListener(new MessageListenerConcurrently() {
            @Override
            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
                for (MessageExt msg : msgs) {
                    System.out.println("消息id:"+msg.getMsgId() + "---" + new String(msg.getBody()));
                }
                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
            }
        });
        consumer.start();
    }

}

4.运行结果：

生产者运行结果：

消费者运行结果：

• rocetmq幂等性问题：

在Activemq中 jms规范支持两种消息模型：点对点和发布订阅，在rocketmq中 有两种消费模式：广播消费,和集群消费。

在消费的过程中，如果消费者出现异常或者超时，导致mq没有及时的相应消费的状态，则可能让mq重试，重试机制就有可能导致出现幂等性，而rocketmq的幂等性 只会出现在集群消费(类似activemq中的点对点消息模型)

生产者：

package com.example.producer;

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;

public class Producer {
    public static void main(String[] args) throws MQClientException {
        DefaultMQProducer producer = new DefaultMQProducer("producer-group");
        producer.setNamesrvAddr("192.168.31.169:9876;192.168.31.177:9876");
        producer.setInstanceName("producer");
        producer.start();
        try {
            for (int i = 0; i < 10; i++) {
                Message msg = new Message("topic", // topic 主题名称
                        "msg", // pull 临时值 在消费者消费的时候 可以根据msg类型进行消费
                        (i + "条消息").getBytes()// body 内容
                );
                SendResult sendResult = producer.send(msg);
                System.out.println(sendResult.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        producer.shutdown();
    }

}

消费者：

package com.example.consumer;

import java.util.List;

import com.alibaba.rocketmq.client.consumer.DefaultMQPushConsumer;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
import com.alibaba.rocketmq.client.consumer.listener.MessageListenerConcurrently;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.common.message.MessageExt;

public class Consumer {
    public static void main(String[] args) throws MQClientException {
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer-group");

        consumer.setNamesrvAddr("192.168.31.169:9876;192.168.31.177:9876");
        consumer.setInstanceName("consumer");
        consumer.subscribe("topic1", "msg");

        consumer.registerMessageListener(new MessageListenerConcurrently() {
            @Override
            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
                for (MessageExt msg : msgs) {
                    System.out.println("消息id:" + msg.getMsgId() + "---" + new String(msg.getBody()));
                }
                // 超时的情况 或者程序异常
                int i = 2 / 0;
                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
            }
        });
        consumer.start();
    }

}

消费结果：

消息id:C0A81FB100002A9F00000000000268EC---5条消息
消息id:C0A81FB100002A9F000000000002686E---4条消息
消息id:C0A81FA900002A9F0000000000037E6A---1条消息
消息id:C0A81FB100002A9F000000000002696A---6条消息
消息id:C0A81FB100002A9F00000000000269E8---7条消息
消息id:C0A81FA900002A9F0000000000038062---9条消息
消息id:C0A81FA900002A9F0000000000037EE8---2条消息
消息id:C0A81FA900002A9F0000000000037FE4---8条消息
消息id:C0A81FA900002A9F0000000000037F66---3条消息
消息id:C0A81FA900002A9F0000000000037DEC---0条消息
消息id:C0A81FA900002A9F0000000000038704---1条消息
消息id:C0A81FA900002A9F000000000003880C---9条消息
消息id:C0A81FA900002A9F0000000000038914---2条消息
消息id:C0A81FA900002A9F0000000000038A1C---0条消息
消息id:C0A81FA900002A9F0000000000038B24---3条消息
消息id:C0A81FA900002A9F0000000000038C2C---8条消息
消息id:C0A81FB100002A9F0000000000026E7E---4条消息
消息id:C0A81FB100002A9F0000000000026F86---7条消息
消息id:C0A81FB100002A9F0000000000027196---5条消息
消息id:C0A81FB100002A9F000000000002708E---6条消息

在Activimq中,可以通过消息id 来作为全局变量，检测是不是重复消费。但是在rocketmq中消费重试的结果中，任意选出两条相同的消息，可以看出 重试的时候消息id是不同的，此时在用消息id作为全局变量判断是否重复消费显然是不可能的。rocketmq中提供了一个消息的key，可以将业务id作为该key。例如：订单号什么的。可以将消息设置的key 在第一次消费的时候存放到数据库之中

幂等性消费者：

package com.example.consumer;

import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.alibaba.rocketmq.client.consumer.DefaultMQPushConsumer;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyContext;
import com.alibaba.rocketmq.client.consumer.listener.ConsumeConcurrentlyStatus;
import com.alibaba.rocketmq.client.consumer.listener.MessageListenerConcurrently;
import com.alibaba.rocketmq.client.exception.MQClientException;
import com.alibaba.rocketmq.common.message.MessageExt;

public class Consumer {
    public static Map<String, String> map = new HashMap<String, String>();// 模拟内存，实际情况可以将key放在redis之中

    public static void main(String[] args) throws MQClientException {
        DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("consumer-group");
        consumer.setNamesrvAddr("192.168.31.169:9876;192.168.31.177:9876");
        consumer.setInstanceName("consumer");
        consumer.subscribe("topic1", "msg");

        consumer.registerMessageListener(new MessageListenerConcurrently() {
            @Override
            public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs, ConsumeConcurrentlyContext context) {
                for (MessageExt msg : msgs) {
                    if (!map.containsKey(msg.getKeys())) {
                        // 如果此时的业务逻辑是将收到的消息存放到数据库
                        System.out.println("消息id:" + msg.getMsgId() + "---" + new String(msg.getBody()));
                        map.put(msg.getKeys(), new String(msg.getBody()));
                    } else {
                        System.out.println("重复消费");
                        return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
                    }
                }
                // 超时的情况 或者程序异常
                int i = 2 / 0;
                return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
            }
        });
        consumer.start();
    }

}