Messaging with Redis

This guide walks you through the process of using Spring Data Redis to publish and subscribe to messages sent with Redis.

What You Will build

You will build an application that uses StringRedisTemplate to publish a string message and has a POJO subscribe for the message by using MessageListenerAdapter.

It may sound strange to be using Spring Data Redis as the means to publish messages, but, as you will discover, Redis provides not only a NoSQL data store but a messaging system as well.

What You Need

About 15 minutes
A favorite text editor or IDE
JDK 1.8 or later
Gradle 4+ or Maven 3.2+
You can also import the code straight into your IDE:
- Spring Tool Suite (STS)
- IntelliJ IDEA
  - A Redis server (See Standing up a Redis server)

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Standing up a Redis server.

To skip the basics, do the following:

Download and unzip the source repository for this guide, or clone it using Git: git clone https://github.com/spring-guides/gs-messaging-redis.git
cd into gs-messaging-redis/initial
Jump ahead to Starting with Spring Initializr.

When you finish, you can check your results against the code in gs-messaging-redis/complete.

Standing up a Redis server

Before you can build a messaging application, you need to set up the server that will handle receiving and sending messages.

Redis is an open source, BSD-licensed, key-value data store that also comes with a messaging system. The server is freely available at https://redis.io/download. You can download it manually, or, if you use a Mac, with Homebrew, by running the following command in a terminal window:

brew install redis

Once you unpack Redis, you can launch it with its default settings by running the following command:

redis-server

You should see a message similar to the following:

[35142] 01 May 14:36:28.939 # Warning: no config file specified, using the default config. In order to specify a config file use redis-server /path/to/redis.conf
[35142] 01 May 14:36:28.940 * Max number of open files set to 10032
                _._
              _.-``__ ''-._
        _.-``    `.  `_.  ''-._           Redis 2.6.12 (00000000/0) 64 bit
    .-`` .-```.  ```\/    _.,_ ''-._
  (    '      ,       .-`  | `,    )     Running in stand alone mode
  |`-._`-...-` __...-.``-._|'` _.-'|     Port: 6379
  |    `-._   `._    /     _.-'    |     PID: 35142
    `-._    `-._  `-./  _.-'    _.-'
  |`-._`-._    `-.__.-'    _.-'_.-'|
  |    `-._`-._        _.-'_.-'    |           https://redis.io
    `-._    `-._`-.__.-'_.-'    _.-'
  |`-._`-._    `-.__.-'    _.-'_.-'|
  |    `-._`-._        _.-'_.-'    |
    `-._    `-._`-.__.-'_.-'    _.-'
        `-._    `-.__.-'    _.-'
            `-._        _.-'
                `-.__.-'

[35142] 01 May 14:36:28.941 # Server started, Redis version 2.6.12
[35142] 01 May 14:36:28.941 * The server is now ready to accept connections on port 6379

Starting with Spring Initializr

You can use this pre-initialized project and click Generate to download a ZIP file. This project is configured to fit the examples in this tutorial.

To manually initialize the project:

Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you.
Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java.
Click Dependencies and select Spring Data Redis.
Click Generate.
Download the resulting ZIP file, which is an archive of a web application that is configured with your choices.

If your IDE has the Spring Initializr integration, you can complete this process from your IDE.

You can also fork the project from Github and open it in your IDE or other editor.

Create a Redis Message Receiver

In any messaging-based application, there are message publishers and messaging receivers. To create the message receiver, implement a receiver with a method to respond to messages, as the following example (from src/main/java/com/example/messagingredis/Receiver.java) shows:

package com.example.messagingredis;

import java.util.concurrent.atomic.AtomicInteger;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Receiver {
    private static final Logger LOGGER = LoggerFactory.getLogger(Receiver.class);

    private AtomicInteger counter = new AtomicInteger();

    public void receiveMessage(String message) {
        LOGGER.info("Received <" + message + ">");
        counter.incrementAndGet();
    }

    public int getCount() {
        return counter.get();
    }
}

The Receiver is a POJO that defines a method for receiving messages. When you register the Receiver as a message listener, you can name the message-handling method whatever you want.

For demonstration purposes, the receiver is counting the messages received. That way, it can signal when it has received a message.

Register the Listener and Send a Message

Spring Data Redis provides all the components you need to send and receive messages with Redis. Specifically, you need to configure:

A connection factory
A message listener container
A Redis template

You will use the Redis template to send messages, and you will register the Receiver with the message listener container so that it will receive messages. The connection factory drives both the template and the message listener container, letting them connect to the Redis server.

This example uses Spring Boot’s default RedisConnectionFactory, an instance of JedisConnectionFactory that is based on the Jedis Redis library. The connection factory is injected into both the message listener container and the Redis template, as the following example (from src/main/java/com/example/messagingredis/MessagingRedisApplication.java) shows:

package com.example.messagingredis;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.listener.PatternTopic;
import org.springframework.data.redis.listener.RedisMessageListenerContainer;
import org.springframework.data.redis.listener.adapter.MessageListenerAdapter;

@SpringBootApplication
public class MessagingRedisApplication {

	private static final Logger LOGGER = LoggerFactory.getLogger(MessagingRedisApplication.class);

	@Bean
	RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory,
			MessageListenerAdapter listenerAdapter) {

		RedisMessageListenerContainer container = new RedisMessageListenerContainer();
		container.setConnectionFactory(connectionFactory);
		container.addMessageListener(listenerAdapter, new PatternTopic("chat"));

		return container;
	}

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

	@Bean
	Receiver receiver() {
		return new Receiver();
	}

	@Bean
	StringRedisTemplate template(RedisConnectionFactory connectionFactory) {
		return new StringRedisTemplate(connectionFactory);
	}

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

		ApplicationContext ctx = SpringApplication.run(MessagingRedisApplication.class, args);

		StringRedisTemplate template = ctx.getBean(StringRedisTemplate.class);
		Receiver receiver = ctx.getBean(Receiver.class);

		while (receiver.getCount() == 0) {

			LOGGER.info("Sending message...");
			template.convertAndSend("chat", "Hello from Redis!");
			Thread.sleep(500L);
		}

		System.exit(0);
	}
}

The bean defined in the listenerAdapter method is registered as a message listener in the message listener container defined in container and will listen for messages on the chat topic. Because the Receiver class is a POJO, it needs to be wrapped in a message listener adapter that implements the MessageListener interface (which is required by addMessageListener()). The message listener adapter is also configured to call the receiveMessage() method on Receiver when a message arrives.

The connection factory and message listener container beans are all you need to listen for messages. To send a message, you also need a Redis template. Here, it is a bean configured as a StringRedisTemplate, an implementation of RedisTemplate that is focused on the common use of Redis, where both keys and values are String instances.

The main() method kicks off everything by creating a Spring application context. The application context then starts the message listener container, and the message listener container bean starts listening for messages. The main() method then retrieves the StringRedisTemplate bean from the application context and uses it to send a Hello from Redis! message on the chat topic. Finally, it closes the Spring application context, and the application ends.

Build an executable JAR

You can run the application from the command line with Gradle or Maven. You can also build a single executable JAR file that contains all the necessary dependencies, classes, and resources and run that. Building an executable jar makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you use Gradle, you can run the application by using ./gradlew bootRun. Alternatively, you can build the JAR file by using ./gradlew build and then run the JAR file, as follows:

java -jar build/libs/gs-messaging-redis-0.1.0.jar

If you use Maven, you can run the application by using ./mvnw spring-boot:run. Alternatively, you can build the JAR file with ./mvnw clean package and then run the JAR file, as follows:

java -jar target/gs-messaging-redis-0.1.0.jar

The steps described here create a runnable JAR. You can also build a classic WAR file.

You should see output similar to the following:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.8.RELEASE)

2019-09-23 12:57:11.578  INFO 35396 --- [           main] c.e.m.MessagingRedisApplication          : Starting MessagingRedisApplication on Jays-MBP with PID 35396 (/Users/j/projects/guides/gs-messaging-redis/complete/target/classes started by j in /Users/j/projects/guides/gs-messaging-redis/complete)
2019-09-23 12:57:11.581  INFO 35396 --- [           main] c.e.m.MessagingRedisApplication          : No active profile set, falling back to default profiles: default
2019-09-23 12:57:11.885  INFO 35396 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Multiple Spring Data modules found, entering strict repository configuration mode!
2019-09-23 12:57:11.887  INFO 35396 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data repositories in DEFAULT mode.
2019-09-23 12:57:11.914  INFO 35396 --- [           main] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 13ms. Found 0 repository interfaces.
2019-09-23 12:57:12.685  INFO 35396 --- [    container-1] io.lettuce.core.EpollProvider            : Starting without optional epoll library
2019-09-23 12:57:12.685  INFO 35396 --- [    container-1] io.lettuce.core.KqueueProvider           : Starting without optional kqueue library
2019-09-23 12:57:12.848  INFO 35396 --- [           main] c.e.m.MessagingRedisApplication          : Started MessagingRedisApplication in 1.511 seconds (JVM running for 3.685)
2019-09-23 12:57:12.849  INFO 35396 --- [           main] c.e.m.MessagingRedisApplication          : Sending message...
2019-09-23 12:57:12.861  INFO 35396 --- [    container-2] com.example.messagingredis.Receiver      : Received <Hello from Redis!>

Summary

Congratulations! You have just developed a publish-and-subscribe application with Spring and Redis.

Redis support is available.