/gs-messaging-redis

Messaging with Redis :: Learn how to use Redis as a message broker.

Primary LanguageJava

Table of Contents

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

What you’ll build

You’ll build an application that uses StringRedisTemplate to publish a string message and has a POJO subscribe for it using MessageListenerAdapter.

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

What you’ll need

+ - Redis server (installation instructions below)

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 http://redis.io/download. You can download it manually, or if you use a Mac with homebrew:

brew install redis

Once you unpack Redis, you can launch it with default settings.

redis-server

You should see a message like this:

[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
    `-._    `-._  `-./  _.-'    _.-'
  |`-._`-._    `-.__.-'    _.-'_.-'|
  |    `-._`-._        _.-'_.-'    |           http://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

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:

src/main/java/hello/Receiver.java

link:complete/src/main/java/hello/Receiver.java[role=include]

The Receiver is a simple POJO that defines a method for receiving messages. As you’ll see when you register the Receiver as a message listener, you can name the message-handling method whatever you want.

Note
 For demonstration purposes, it is autowired by its constructor with a countdown latch. 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’ll 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, enabling them to connect to the Redis server.

This example uses Spring Boot’s default RedisConnectionFactory, an instance of JedisConnectionFactory which is based on the Jedis Redis library. The connection factory is injected into both the message listener container and the Redis template.

src/main/java/hello/Application.java

link:complete/src/main/java/hello/Application.java[role=include]

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 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`s.

The main() method kicks everything off 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.

You should see the following output:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.5.RELEASE)

2014-04-18 08:03:34.032  INFO 47002 --- [           main] hello.Application                        : Starting Application on retina with PID 47002 (/Users/gturnquist/src/spring-guides/gs-messaging-redis/complete/target/classes started by gturnquist)
2014-04-18 08:03:34.062  INFO 47002 --- [           main] s.c.a.AnnotationConfigApplicationContext : Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@7a53c84a: startup date [Fri Apr 18 08:03:34 CDT 2014]; root of context hierarchy
2014-04-18 08:03:34.326  INFO 47002 --- [           main] o.s.c.support.DefaultLifecycleProcessor  : Starting beans in phase 2147483647
2014-04-18 08:03:34.357  INFO 47002 --- [           main] hello.Application                        : Started Application in 0.605 seconds (JVM running for 0.899)
2014-04-18 08:03:34.357  INFO 47002 --- [           main] hello.Application                        : Sending message...
2014-04-18 08:03:34.370  INFO 47002 --- [    container-2] hello.Receiver                           : Received <Hello from Redis!>
2014-04-18 08:03:34.379  INFO 47002 --- [       Thread-1] s.c.a.AnnotationConfigApplicationContext : Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@7a53c84a: startup date [Fri Apr 18 08:03:34 CDT 2014]; root of context hierarchy
2014-04-18 08:03:34.380  INFO 47002 --- [       Thread-1] o.s.c.support.DefaultLifecycleProcessor  : Stopping beans in phase 2147483647

Summary

Congratulations! You’ve just developed a simple publish-and-subscribe application with Spring and Redis.

Note
 Redis support is available.

See Also

The following guides may also be helpful: