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 {
    @Autowired
    private RedissonClient client;

    private static final String REDIS_QUEUE = "list_queue";

    private static final Logger LOGGER = LoggerFactory.getLogger(RedisListTest.class);
    
    @Test
    public 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);
    }

    @Override
    public 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 {
    @Bean
    public MessageListenerAdapter messageListenerAdapter() {
        return new MessageListenerAdapter(new MyMessageListener());
    }

    @Bean
    public 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 {
    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    @Test
    public 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