redis订阅发布示例

下面的代码使用redis实现订阅/发布。需要jedis的2.0.0和SLF4J的jar包。

在redis中可以同时订阅多个频道，如果有消息发布是redis会发出通知。jedis中提供了JedisPubSub抽象类来提供发布/订阅的机制，在实际应用中需要实现JedisPubSub类。

package cn.outofmemory.redis;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import redis.clients.jedis.JedisPubSub;

public class Subscriber extends JedisPubSub {

private static Logger logger = LoggerFactory.getLogger(Subscriber.class);

@Override
public void onMessage(String channel, String message) {
logger.info("Message received. Channel: {}, Msg: {}", channel, message);
}

@Override
public void onPMessage(String pattern, String channel, String message) {

}

@Override
public void onSubscribe(String channel, int subscribedChannels) {

}

@Override
public void onUnsubscribe(String channel, int subscribedChannels) {

}

@Override
public void onPUnsubscribe(String pattern, int subscribedChannels) {

}

@Override
public void onPSubscribe(String pattern, int subscribedChannels) {

}
}

上面的类是从JedisPubSub继承的类，我要用它来订阅一些频道，并获得消息。

main方法如下

package cn.outofmemory.redis;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

public class Program {

public static final String CHANNEL_NAME = "commonChannel";

private static Logger logger = LoggerFactory.getLogger(Program.class);

public static void main(String[] args) throws Exception {

JedisPoolConfig poolConfig = new JedisPoolConfig();

JedisPool jedisPool = new JedisPool(poolConfig, "localhost", 6379, 0);

final Jedis subscriberJedis = jedisPool.getResource();

final Subscriber subscriber = new Subscriber();

new Thread(new Runnable() {
@Override
public void run() {
try {
logger.info("Subscribing to \"commonChannel\". This thread will be blocked.");
subscriberJedis.subscribe(subscriber, CHANNEL_NAME);
logger.info("Subscription ended.");
} catch (Exception e) {
logger.error("Subscribing failed.", e);
}
}
}).start();

Jedis publisherJedis = jedisPool.getResource();

new Publisher(publisherJedis, CHANNEL_NAME).start();

subscriber.unsubscribe();
jedisPool.returnResource(subscriberJedis);
jedisPool.returnResource(publisherJedis);
}
}

在上面的例子中，我们使用JedisPool来获得Jedis的实例。 Jedis类是非线程安全的，但是JedisPool是线程安全的。我使用了两个Jedis实例，一个用来发布消息，另一个订阅频道。

我在另外一个线程中实现订阅。

下面的类实现发布消息到redis的频道中。

package cn.outofmemory.redis;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import redis.clients.jedis.Jedis;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Publisher {

private static final Logger logger = LoggerFactory.getLogger(Publisher.class);

private final Jedis publisherJedis;

private final String channel;

public Publisher(Jedis publisherJedis, String channel) {
this.publisherJedis = publisherJedis;
this.channel = channel;
}

public void start() {
logger.info("Type your message (quit for terminate)");
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

while (true) {
String line = reader.readLine();

if (!"quit".equals(line)) {
publisherJedis.publish(channel, line);
} else {
break;
}
}

} catch (IOException e) {
logger.error("IO failure while reading input, e");
}
}
}

上面的类获得用户的控制台输入，然后发布到redis channel，当用户键入quit时则退出循环

关键点如下：
要在单独的线程中订阅, 因为subscribe会阻塞当前线程的执行。 你可以使用一个PubSub实例来订阅多个Channel
注意Jedis实例是非线程安全的
当需要创建多个jedis实例时要使用JedisPool类，当使用完jedis对象时要放回JedisPool。