Redis pub/sub Using Spring

Continuing to discover the powerful set of Redis features, the one worth mentioning about is out of the box support of pub/sub messaging.

Pub/Sub messaging is essential part of many software architectures. Some software systems demand from messaging solution to provide high-performance, scalability, queues persistence and durability, fail-over support, transactions, and many more nice-to-have features, which in Java world mostly always leads to using one of JMS implementation providers. In my previous projects I have actively used Apache ActiveMQ (now moving towards Apache ActiveMQ Apollo). Though it's a great implementation, sometimes I just needed simple queuing support and Apache ActiveMQ just looked overcomplicated for that.

Alternatives? Please welcome Redis pub/sub! If you are already using Redis as key/value store, few additional lines of configuration will bring pub/sub messaging to your application in no time.

Spring Data Redis project abstracts very well Redis pub/sub API and provides the model so familiar to everyone who uses Spring capabilities to integrate with JMS.

As always, let's start with the POM configuration file. It's pretty small and simple, includes necessary Spring dependencies, Spring Data Redis and Jedis, great Java client for Redis.

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelversion>4.0.0</modelversion>
    <groupid>com.example.spring</groupid>
    <artifactid>redis</artifactid>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <properties>
        <project.build.sourceencoding>UTF-8</project.build.sourceencoding>
        <spring.version>3.1.1.RELEASE</spring.version>
    </properties>

    <dependencies>
        <dependency>
            <groupid>org.springframework.data</groupid>
            <artifactid>spring-data-redis</artifactid>
            <version>1.0.1.RELEASE</version>
        </dependency>

        <dependency>
            <groupid>cglib</groupid>
            <artifactid>cglib-nodep</artifactid>
            <version>2.2</version>
        </dependency>

        <dependency>
            <groupid>log4j</groupid>
            <artifactid>log4j</artifactid>
            <version>1.2.16</version>
        </dependency>

        <dependency>
            <groupid>redis.clients</groupid>
            <artifactid>jedis</artifactid>
            <version>2.0.0</version>
            <type>jar</type>
        </dependency>

        <dependency>
            <groupid>org.springframework</groupid>
            <artifactid>spring-core</artifactid>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupid>org.springframework</groupid>
            <artifactid>spring-context</artifactid>
            <version>${spring.version}</version>
           </dependency>
       </dependencies>

       <build>
           <plugins>
               <plugin>
                   <groupid>org.apache.maven.plugins</groupid>
                   <artifactid>maven-compiler-plugin</artifactid>
                   <version>2.3.2</version>
                   <configuration>
                       <source>1.6
                       <target>1.6</target>
                   </configuration>
               </plugin>
           </plugins>
    </build>
</project>

Moving on to configuring Spring context, let's understand what we need to have in order for a publisher to publish some messages and for a consumer to consume them. Knowing the respective Spring abstractions for JMS will help a lot with that.

we need connection factory -> JedisConnectionFactory
we need a template for publisher to publish messages -> RedisTemplate
we need a message listener for consumer to consume messages -> RedisMessageListenerContainer

Using Spring Java configuration, let's describe our context:

package com.example.redis.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.listener.ChannelTopic;
import org.springframework.data.redis.listener.RedisMessageListenerContainer;
import org.springframework.data.redis.listener.adapter.MessageListenerAdapter;
import org.springframework.data.redis.serializer.GenericToStringSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;
import org.springframework.scheduling.annotation.EnableScheduling;

import com.example.redis.IRedisPublisher;
import com.example.redis.impl.RedisMessageListener;
import com.example.redis.impl.RedisPublisherImpl;

@Configuration
@EnableScheduling
public class AppConfig {
    @Bean
    JedisConnectionFactory jedisConnectionFactory() {
        return new JedisConnectionFactory();
    }

    @Bean
    RedisTemplate< String, Object > redisTemplate() {
        final RedisTemplate< String, Object > template =  new RedisTemplate< String, Object >();
        template.setConnectionFactory( jedisConnectionFactory() );
        template.setKeySerializer( new StringRedisSerializer() );
        template.setHashValueSerializer( new GenericToStringSerializer< Object >( Object.class ) );
        template.setValueSerializer( new GenericToStringSerializer< Object >( Object.class ) );
        return template;
    }

    @Bean
    MessageListenerAdapter messageListener() {
        return new MessageListenerAdapter( new RedisMessageListener() );
    }

    @Bean
    RedisMessageListenerContainer redisContainer() {
        final RedisMessageListenerContainer container = new RedisMessageListenerContainer();

        container.setConnectionFactory( jedisConnectionFactory() );
        container.addMessageListener( messageListener(), topic() );

        return container;
    }

    @Bean
    IRedisPublisher redisPublisher() {
        return new RedisPublisherImpl( redisTemplate(), topic() );
    }

    @Bean
    ChannelTopic topic() {
        return new ChannelTopic( "pubsub:queue" );
    }
}

Very easy and straightforward. The presence of @EnableScheduling annotation is not necessary and is required only for our publisher implementation: the publisher will publish a string message every 100 ms.

package com.example.redis.impl;

import java.util.concurrent.atomic.AtomicLong;

import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.listener.ChannelTopic;
import org.springframework.scheduling.annotation.Scheduled;

import com.example.redis.IRedisPublisher;

public class RedisPublisherImpl implements IRedisPublisher {
    private final RedisTemplate< String, Object > template;
    private final ChannelTopic topic; 
    private final AtomicLong counter = new AtomicLong( 0 );

    public RedisPublisherImpl( final RedisTemplate< String, Object > template, 
            final ChannelTopic topic ) {
        this.template = template;
        this.topic = topic;
    }

    @Scheduled( fixedDelay = 100 )
    public void publish() {
        template.convertAndSend( topic.getTopic(), "Message " + counter.incrementAndGet() + 
            ", " + Thread.currentThread().getName() );
 }
}

And finally our message listener implementation (which just prints message on a console).

package com.example.redis.impl;

import org.springframework.data.redis.connection.Message;
import org.springframework.data.redis.connection.MessageListener;

public class RedisMessageListener implements MessageListener {
    @Override
    public void onMessage( final Message message, final byte[] pattern ) {
        System.out.println( "Message received: " + message.toString() );
    }
}

Awesome, just two small classes, one configuration to wire things together and we have full pub/sub messaging support in our application! Let's run the application as standalone ...

package com.example.redis;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.example.redis.config.AppConfig;

public class RedisPubSubStarter {
    public static void main(String[] args) {
        new AnnotationConfigApplicationContext( AppConfig.class );
    }
}

... and see following output in a console:

...
Message received: Message 1, pool-1-thread-1
Message received: Message 2, pool-1-thread-1
Message received: Message 3, pool-1-thread-1
Message received: Message 4, pool-1-thread-1
Message received: Message 5, pool-1-thread-1
Message received: Message 6, pool-1-thread-1
Message received: Message 7, pool-1-thread-1
Message received: Message 8, pool-1-thread-1
Message received: Message 9, pool-1-thread-1
Message received: Message 10, pool-1-thread-1
Message received: Message 11, pool-1-thread-1
Message received: Message 12, pool-1-thread-1
Message received: Message 13, pool-1-thread-1
Message received: Message 14, pool-1-thread-1
Message received: Message 15, pool-1-thread-1
Message received: Message 16, pool-1-thread-1
...

Great! There is much more which you could do with Redis pub/sub, excellent documentation is available for you on Redis official web site.

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