Redis-过期键监听的应用

迈不过友情╰ 2022-12-29 02:18 127阅读 0赞

#### Redis-过期键监听的应用 ####

> 1、应用场景  
> 前期的一个项目，其中一个功能是定时控制楼宇的灯。网关走的4G无线网络，在实际运行中，不时会有一两个灯没有关掉或者打开。经过分析，由于4G网络的不稳定性比较大，断线重连时常发生，若此时正好处于服务器指令发送时间段，会导致指令无法送达。

> 2、当时采用的解决方案是生成冗余指令，把冗余指令放入redis,并设置过期时间。程序对过期事件进行监听，根据约定的key规则，过滤出我们需要的key,进行下一步操作

> 3、相关依赖

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

> 4、继承MessageListenerAdapter，自定义监听器，此种方式可以在注册监听器时设置topic，对具体的一个database进行监听。

@Slf4j
    @Component
    public class RedisKeyExpirationListener extends MessageListenerAdapter { 
        @Override
        public void onMessage(Message message, byte[] pattern) { 
            String key = message.toString();
            log.info("Redis监听信息:{}",key);
            if (StringUtils.isNotBlank(key)){ 
                if (key.startsWith("confirm_on_")){ 
                    // 重复开确认
                }
                if (key.startsWith("confirm_off_")){ 
                    // 重复关确认
                }
            }
        }
    }

> 5、配置RedisMessageListenerContainer并注册监听器

@Configuration
    public class RedisListenerConfig { 
        @Autowired
        private RedisKeyExpirationListener redisKeyExpirationListener;
        @Value("${spring.redis.database:0}")
        private int database;
    
        @Bean
        RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory){ 
            RedisMessageListenerContainer container = new RedisMessageListenerContainer();
            container.setConnectionFactory(connectionFactory);
            container.addMessageListener(redisKeyExpirationListener, new PatternTopic("__keyevent@" + database + "__:expired"));
            return container;
        }
    }

> 6、更改redis配置文件，放开注释或者添加以下内容，重启redis

notify-keyspace-events Ex

> 7、扩展一：继承KeyExpirationEventMessageListener的监听器，构造函数传入的是RedisMessageListenerContainer ,监听器会把自己注册进去。特别注意的是这种写法是监听所有的database，并且不能指定。TOPIC如下  
> private static final Topic KEYEVENT\_EXPIRED\_TOPIC = new PatternTopic(“**keyevent@\***:expired”);

@Slf4j
    @Component
    public class RedisKeyExpirationListener2 extends KeyExpirationEventMessageListener { 
        public RedisKeyExpirationListener2(RedisMessageListenerContainer listenerContainer) { 
            super(listenerContainer);
        }
    
        /** * 针对 redis 数据失效事件，进行数据处理 * @param message * @param pattern */
        @Override
        public void onMessage(Message message, byte[] pattern) { 
            // 获取到失效的 key，进行业务处理
            String expiredKey = message.toString();
            log.info("监听失效key:{}",expiredKey);
        }
    }

> 8、扩展二：redis设置相关，键空间和键事件相关，来自配置文件。

############################# EVENT NOTIFICATION ##############################
    
    # Redis can notify Pub/Sub clients about events happening in the key space.
    # This feature is documented at http://redis.io/topics/notifications
    #
    # For instance if keyspace events notification is enabled, and a client
    # performs a DEL operation on key "foo" stored in the Database 0, two
    # messages will be published via Pub/Sub:
    #
    # PUBLISH __keyspace@0__:foo del
    # PUBLISH __keyevent@0__:del foo
    #
    # It is possible to select the events that Redis will notify among a set
    # of classes. Every class is identified by a single character:
    #
    # K Keyspace events, published with __keyspace@<db>__ prefix.
    # E Keyevent events, published with __keyevent@<db>__ prefix.
    # g Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
    # $ String commands
    # l List commands
    # s Set commands
    # h Hash commands
    # z Sorted set commands
    # x Expired events (events generated every time a key expires)
    # e Evicted events (events generated when a key is evicted for maxmemory)
    # A Alias for g$lshzxe, so that the "AKE" string means all the events.
    #
    # The "notify-keyspace-events" takes as argument a string that is composed
    # of zero or multiple characters. The empty string means that notifications
    # are disabled.
    #
    # Example: to enable list and generic events, from the point of view of the
    # event name, use:
    #
    # notify-keyspace-events Elg
    #
    # Example 2: to get the stream of the expired keys subscribing to channel
    # name __keyevent@0__:expired use:
    #
    # notify-keyspace-events Ex
    #
    # By default all notifications are disabled because most users don't need
    # this feature and the feature has some overhead. Note that if you don't
    # specify at least one of K or E, no events will be delivered.
    # notify-keyspace-events Ex

> 小尾巴~~  
> 只要有积累，就会有进步