要知道redis是有消息的發(fā)布和訂閱功能的，我們可以利用它的發(fā)布和訂閱功能非常簡單地實現(xiàn)一些比較實用的功能。

打個比方，如何實現(xiàn)自動關閉超時未支付的訂單？

我們通常的做法是寫一個定時器，定時去掃描未支付的訂單，當發(fā)現(xiàn)下單時間超過我們設置的閾值時就去關閉訂單。 這樣做有一個問題：訂單可能會延時關閉，假如設置5分鐘掃描一次未支付訂單，未支付訂單有效時間是15分鐘，那么就有可能一些訂單到了(15+5)分鐘-1秒才會被關閉。

那么這個時候使用redis發(fā)布訂閱功能就非常方便了，我們只需要在用戶下訂單的時候把訂單號作為key寫入redis，并設置一個15分鐘的有效期。然后訂閱這個key的過期事件，如果用戶在15分鐘之內(nèi)支付了訂單我們就直接刪除這個key。如果到了15分鐘key自動過期了，我們就會接收到redis的消息通知，這個時候就可以直接關閉訂單了。

開啟redis消息訂閱

打開redis.config配置文件，搜索notify-keyspace-events就會看到redis發(fā)布訂閱的配置:

# 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

redis接收事件類型一共有兩種，keyspace和keyevent。keyspace是key觸發(fā)的具體操作，keyevent為操作影響的鍵名。g,$,l,s,h,z,x,e,A表示監(jiān)聽什么樣的事件。

舉個例子我們配置訂閱類型為KEx，我們就可以接收到兩種key過期后產(chǎn)生的消息。

notify-keyspace-events "KEx" #設置監(jiān)聽類型

重啟redis。

開始監(jiān)聽redis消息訂閱

開啟三個客戶端：
訂閱redis key為kname的事件

127.0.0.1:6379> subscribe __keyspace@0__:kname
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "__keyspace@0__:kname"
3) (integer) 1

訂閱redis key 的過期事件

127.0.0.1:6379> subscribe __keyevent@0__:expired
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "__keyevent@0__:expired"
3) (integer) 1

設置kname為zhangsan過期時間為2秒

127.0.0.1:6379> set kname "zhansan" ex 2 

兩秒后訂閱的客戶端分別收到了redis的消息通知

127.0.0.1:6379> subscribe __keyspace@0__:kname
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "__keyspace@0__:kname"
3) (integer) 1
1) "message"
2) "__keyspace@0__:kname"
3) "expired"  #監(jiān)聽到kname過期了

127.0.0.1:6379> subscribe __keyevent@0__:expired
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "__keyevent@0__:expired"
3) (integer) 1
1) "message"
2) "__keyevent@0__:expired"
3) "kname"  #監(jiān)聽到有一個過期的key為kname

上面這個訂閱到一個redis庫的事件，要想訂閱所有的redis庫就需要使用通配符了。

psubscribe __key*@*__:* # 這里注意通配的命令是p開頭

在springboot里如何訂閱redis事件

添加pom依賴

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

yaml文件配置

server:
  port: 8098
spring:
  application:
    name: redis-subscribe-service
  redis:
    host: 127.0.0.1
    port: 6379
    password: red123456

編寫訂閱service

package com.me.binf.service;

import org.springframework.stereotype.Service;

@Service
public class MessageReceiver {
    //接收消息的方法
    public void receiveMessage(String message){
        //message接收到的過期key
        System.out.println("Redis 監(jiān)聽到過期的key有:"+message);
    }
}

添加redis配置

package com.me.binf.config;

import com.icodingedu.supermall.service.MessageReceiver;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.listener.PatternTopic;
import org.springframework.data.redis.listener.RedisMessageListenerContainer;
import org.springframework.data.redis.listener.adapter.MessageListenerAdapter;

@Configuration
public class RedisMessageConfig {

    @Bean
    RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory,
                                            MessageListenerAdapter listenerAdapter){
        RedisMessageListenerContainer container = new RedisMessageListenerContainer();
        container.setConnectionFactory(connectionFactory);
        //訂閱觸發(fā)的通道
        container.addMessageListener(listenerAdapter,
                new PatternTopic("__keyevent@0__:expired"));
        return container;
    }

    @Bean
    MessageListenerAdapter listenerAdapter(MessageReceiver receiver){
        return new MessageListenerAdapter(receiver,"receiveMessage");
    }
}

設置kname過期后接收到消息:

Redis 監(jiān)聽到過期的key有:kname