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参考

https://www.cnblogs.com/uniqueDong/p/15904837.html
https://www.cnblogs.com/wzh2010/p/17205390.html
https://blog.csdn.net/qq_16557637/article/details/121015736
https://developer.aliyun.com/article/1095035
https://blog.csdn.net/sco5282/article/details/132904956

消息队列

消息队列可以实现消息解耦、消息路由、异步处理、流量削峰填谷。主流消息队列有kafka, rabbitmq, rocketmq。
Redis也可以实现消息队列。方式有

1. list
2. pub/sub
3. stream

list

redis的list底层是链表，满足先进先出。
list实现队列比较方便。同时可以满足有序，消息去重。缺点是

1. 没有订阅功能，消费者要主动查询队列。而为了避免频繁查询队列消耗CPU资源，可以采用阻塞式查询。redis中阻塞查询命令是brpop。
2. 无法保证可靠性。缺少消息确认机制，无法及时感知遗漏消息，导致数据不一致。

源码

完整项目在https://gitcode.com/zsss1/redis_mq/overview
在pom.xml添加redisson依赖。

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>org.redisson</groupId><artifactId>redisson-spring-boot-starter</artifactId><version>3.40.2</version></dependency>

Redission封装依赖。

@SpringBootTest(classes = DemoApplication.class)
public class RedisListTest {@Autowiredprivate RedissonClient client;private static final String REDIS_QUEUE = "list_queue";private static final Logger LOGGER = LoggerFactory.getLogger(RedisListTest.class);@Testpublic void test_redis_list_mq() throws Exception {RedissonBlockingDeque r;new Thread(() -> {for (int i = 0; i < 10; i++) {producer("message" + i);}}).start();new Thread(() -> {consumer();}).start();Thread.currentThread().join();}// 消费者，阻塞public void consumer() {RBlockingDeque<String> deque = client.getBlockingDeque(REDIS_QUEUE);boolean isCheck = true;while (isCheck) {try {String message = deque.takeLast();System.out.println("consumer: " + message);} catch (InterruptedException e) {LOGGER.error("consumer failed, cause: {}", e.getMessage());}}}// 生产者public void producer(String message) {RBlockingDeque<String> deque = client.getBlockingDeque(REDIS_QUEUE);System.out.println(deque.getClass());try {deque.putFirst(message);} catch (InterruptedException e) {LOGGER.error("producer failed, msg: {}, cause: {}", message, e.getMessage());}}
}

pub/sub

发布订阅模式是一种消息传递模式。发送者将消息发送到频道，订阅者订阅频道即可及时收到消息。
它支持组生产者与消费者。但是它会丢失消息。
Redis在server端为每个消费者保留一块内存区域，存储该消费者订阅的数据。如果消费者处理速度慢，内存区域满了，那么Redis会断开消费者连接，这会导致消息丢失。

源码

1. 定义频道。

public class TopicChannel {public static final String SEND_PHONE = "send_phone";public static final String SEND_EMAIL = "send_email";
}

2. 定义监听频道的订阅者。分清org.springframework.data.redis.connection.MessageListener与org.redisson.api.listener.MessageListener。

public class MyMessageListener implements MessageListener {private static Map<String, Consumer<String>> RULE = new HashMap<>();static {RULE.put(TopicChannel.SEND_EMAIL, MyMessageListener::sendEmail);RULE.put(TopicChannel.SEND_PHONE, MyMessageListener::sendPhone);}public static void sendEmail(String msg) {System.out.println("listen email:" + msg);}public static void sendPhone(String msg) {System.out.println("listen phone:" + msg);}@Overridepublic void onMessage(Message message, byte[] pattern) {byte[] byteChannel = message.getChannel();byte[] byteBody = message.getBody();try {String channel = new String(byteChannel);String body = new String(byteBody);System.out.println("channel: + " + channel + ", body: " + body);RULE.get(channel).accept(body);} catch (Exception e) {System.out.println(e.getMessage());}}
}

3. 在redis注册订阅者。

@Component
public class RedisConfig {@Beanpublic MessageListenerAdapter messageListenerAdapter() {return new MessageListenerAdapter(new MyMessageListener());}@Beanpublic RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory, MessageListenerAdapter messageListenerAdapter) {RedisMessageListenerContainer container = new RedisMessageListenerContainer();container.setConnectionFactory(connectionFactory);// messageListenerAdapter 订阅 SEND_EMAIL 频道container.addMessageListener(messageListenerAdapter, new PatternTopic(TopicChannel.SEND_EMAIL));// messageListenerAdapter 订阅 SEND_PHONE 频道container.addMessageListener(messageListenerAdapter, new PatternTopic(TopicChannel.SEND_PHONE));return container;}
}

4. 测试

@SpringBootTest(classes = DemoApplication.class)
public class MyListener {@Autowiredprivate RedisTemplate<String, String> redisTemplate;@Testpublic void test_pub() {redisTemplate.convertAndSend(TopicChannel.SEND_EMAIL, "pub email message");redisTemplate.convertAndSend(TopicChannel.SEND_PHONE, "pub phone message");}
}

测试结果

channel: + send_email, body: pub email message
listen email:pub email message
channel: + send_phone, body: pub phone message
listen phone:pub phone message