思考
情景
有一个这样的场景,某系统里为用户开辟了一个空间,这个空间在有效期里可以随意使用。但是到期后要回收。我们可以通过定时任务对数据库表中存在的空间信息进行检查,如果截止时间到了,就进行对应的操作。也可以把这个定时的工程扔给系统以外。
另一种思路
我们可以尝试另一种方案,例如创建空间的时候,将空间 id 作为 key 的一部分存放在 redis 中,而 ex 设置为有效时间。在 redis 将这个超时的 key 删除的时候,通知我们系统,从而完成清除空间的操作。
实施
具体实现如下:
1,打开事件
1.1,修改配置文件
默认的 redis 并没有开启这个功能,需要修改配置文件中的 notify-keyspace-events 配置
############################# 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
# by zero or multiple characters. The empty string means that notifications
# are disabled at all.
#
# 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
是的,重点就是:
notify-keyspace-events Ex
Ex 代表:
# 以 “__keyevent@<db>__“ 为前缀发布Keyevent事件,<db>为所使用的redis库编号
1,E: Keyevent events, published with __keyevent@<db>__ prefix.
# 过期事件(每次键过期时生成的事件)
2,x: Expired events (events generated every time a key expires)
1.2,运行时通过参数设置
#设置:
redis-cli: CONFIG SET notify-keyspace-events "Ex"
#查询
redis-cli:CONFIG GET notify-keyspace-event
#redis: 指的是进入redis-cli后,并且执行成功的情况
但是这种重启 redis 服务就没了(恢复为配置文件中的设置)。
2,程序方面
2.1,增加依赖包
pom.xml:
<!-- https://mvnrepository.com/artifact/org.springframework.data/spring-data-redis -->
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-redis</artifactId>
<version>1.8.22.RELEASE</version>
</dependency>
<!-- https://mvnrepository.com/artifact/redis.clients/jedis -->
<dependency>
<groupId>redis.clients</groupId>
<artifactId>jedis</artifactId>
<version>2.10.2</version>
</dependency>
# spring用的是4.3.7.RELEASE。需要注意匹配。
代码:
import org.springframework.data.redis.connection.Message;
import org.springframework.data.redis.connection.MessageListener;
public class RedisKeyExpiredMessageDelegate implements MessageListener {
private final String EVENT_CHANNEL = "__keyevent@0__:expired";
@Override
public void onMessage(Message message, byte[] bytes) {
if (EVENT_CHANNEL.equalsIgnoreCase(new String(message.getChannel()))) {
String msg = new String(message.getBody());
System.out.println(msg + "过期");
}
}
}
spring 配置文件:
<!-- redis 连接工厂 -->
<bean id="redisConnectionFactory" class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory"
p:host-name="localhost"
p:port="6379"/>
<!-- redis消息监听 -->
<bean id="redisMessageListener"
class="org.springframework.data.redis.listener.adapter.MessageListenerAdapter">
<constructor-arg>
<bean class="com.imadiaos.redis.RedisKeyExpiredMessageDelegate" />
</constructor-arg>
</bean>
<bean id="redisContainer"
class="org.springframework.data.redis.listener.RedisMessageListenerContainer">
<property name="connectionFactory" ref="redisConnectionFactory" />
<property name="messageListeners">
<map>
<entry key-ref="redisMessageListener">
<list>
<!-- <bean class="org.springframework.data.redis.listener.ChannelTopic">
<constructor-arg value="__keyevent@1__:expired" /> </bean> -->
<!-- <bean class="org.springframework.data.redis.listener.PatternTopic">
<constructor-arg value="*" /> </bean> -->
<bean class="org.springframework.data.redis.listener.PatternTopic">
<constructor-arg value="__key*__:expired" />
</bean>
</list>
</entry>
</map>
</property>
</bean>
代码示例: github.com/imadiaos
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