1.概述
Redis为我们提供了publish/subscribe
(发布/订阅)功能。我们可以对某个channel(频道)进行subscribe(订阅),当有人在这个channel上publish(发布)消息时,redis就会通知我们,这样我们可以收到别人发布的消息。
作为Java的redis客户端,Jedis提供了publish/subscribe的接口。本文讲述如何使用Jedis来实现redis的publish/subscribe。
2.定义Subscriber类
Jedis定义了抽象类JedisPubSub,在这个类中,定义publish/subsribe的回调方法。通过继承JedisPubSub类并重新实现这些回调方法,当publish/subsribe事件发生时,我们可以定制自己的处理逻辑。
在以下例子中,我们定义了Subscriber类,这个类继承了JedisPubSub类,并重新实现了其中的回调方法。
package com.redis.demo.pubsub;
import redis.clients.jedis.JedisPubSub;
public class Subscriber extends JedisPubSub {
public Subscriber() {
}
public void onMessage(String channel, String message) {
System.out.println(String.format("receive redis published message, channel %s, message %s", channel, message));
}
public void onSubscribe(String channel, int subscribedChannels) {
System.out.println(String.format("subscribe redis channel success, channel %s, subscribedChannels %d",
channel, subscribedChannels));
}
public void onUnsubscribe(String channel, int subscribedChannels) {
System.out.println(String.format("unsubscribe redis channel, channel %s, subscribedChannels %d",
channel, subscribedChannels));
}
}
3.定义SubThread线程类
由于Jedis的subscribe操作是阻塞的,因此,我们另起一个线程来进行subscribe操作。
package com.redis.demo.pubsub;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
public class SubThread extends Thread {
private final JedisPool jedisPool;
private final Subscriber subscriber = new Subscriber();
private final String channel = "mychannel";
public SubThread(JedisPool jedisPool) {
super("SubThread");
this.jedisPool = jedisPool;
}
@Override
public void run() {
System.out.println(String.format("subscribe redis, channel %s, thread will be blocked", channel));
Jedis jedis = null;
try {
jedis = jedisPool.getResource();
jedis.subscribe(subscriber, channel);
} catch (Exception e) {
System.out.println(String.format("subsrcibe channel error, %s", e));
} finally {
if (jedis != null) {
jedis.close();
}
}
}
}
在上面的代码中,我们从JedisPool获取一个Jedis实例,并使用这个Jedis实例进行subscribe的操作。
Jedis的subscribe的声明如下:
public void subscribe(final JedisPubSub jedisPubSub, final String… channels)
第一个参数接受一个JedisPubSub对象,第二个参数指定对哪个频道进行订阅。上例中,我们把我们定义的Subscriber对象传给subscribe方法。
当publish/subscribe的事件发生时,会自动调用我们Subscriber的方法。
4.定义Publisher类
Publisher类接受用户的输入,并将输入发布到channel。当用户输入”quit”后,输入结束。
package com.redis.demo.pubsub;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
public class Publisher {
private final JedisPool jedisPool;
public Publisher(JedisPool jedisPool) {
this.jedisPool = jedisPool;
}
public void start() {
Scanner input = new Scanner(System.in);
Jedis jedis = jedisPool.getResource();
while (true) {
String line = null;
try {
//接受String类型
line = input.next();
if (!"quit".equals(line)) {
jedis.publish("mychannel", line);
} else {
break;
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
}
5.定义入口代码
如下是我们的程序入口代码。
package com.redis.demo.pubsub;
import org.junit.Test;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;
import static org.junit.Assert.*;
public class PublisherTest {
@Test
public void mainTest() {
// 替换成你的reids地址和端口
String redisIp = "localhost";
int reidsPort = 6379;
JedisPool jedisPool = new JedisPool(new JedisPoolConfig(), redisIp, reidsPort);
System.out.println(String.format("redis pool is starting, redis ip %s, redis port %d", redisIp, reidsPort));
SubThread subThread = new SubThread(jedisPool);
subThread.start();
Publisher publisher = new Publisher(jedisPool);
publisher.start();
}
}
在上面的代码中,我们首先生成了一个JedisPool的redis连接池,这是由于Jedis不是线程安全的,JedisPool是线程安全的。而我们的程序在主线程和订阅线程(SubThread)均需要使用Jedis,故在程序中我们使用JedisPool。具体也可以参考在多线程环境中使用Jedis。
由于Jedis的subcribe操作是阻塞的,故我们另起了一个线程来进行subcribe操作。
通过调用Publisher::start()方法,接受用户的输入,并publish到指定的channel。
输出
redis pool is starting, redis ip 192.168.229.154, redis port 6379
subscribe redis, channel mychannel, thread will be blocked
subscribe redis channel success, channel mychannel, subscribedChannels 1
这时输入
aa
控制窗口中输出
receive redis published message, channel mychannel, message aa
这里测试类下无法输入 【IDEA】IDEA 单元测试 System.in 没办法输入