spring-guides / Gs Messaging Redis

:toc: :icons: font :source-highlighter: prettify :project_id: gs-messaging-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.

NOTE: 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

:java_version: 1.8 include::https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/prereq_editor_jdk_buildtools.adoc[] +

• A Redis server (See <>)

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[[scratch]] == 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:

==== [source,bash]

brew install redis

====

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

==== [source,bash]

redis-server

====

You should see a message similar to the following:

==== [source,text]

[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

====

[[initial]] == Starting with Spring Initializr

If you use Maven, visit the https://start.spring.io/#!type=maven-project&language=java&platformVersion=2.4.3.RELEASE&packaging=jar&jvmVersion=1.8&groupId=com.example&artifactId=messaging-redis&name=messaging-redis&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.messaging-redis&dependencies=data-redis[Spring Initializr] to generate a new project with the required dependency (Spring Data Redis).

The following listing shows the pom.xml file that is created when you choose Maven:

==== [src,xml]

include::complete/pom.xml[]

====

If you use Gradle, visit the https://start.spring.io/#!type=gradle-project&language=java&platformVersion=2.4.3.RELEASE&packaging=jar&jvmVersion=1.8&groupId=com.example&artifactId=messaging-redis&name=messaging-redis&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.messaging-redis&dependencies=data-redis[Spring Initializr] to generate a new project with the required dependency (Spring Data Redis).

The following listing shows the build.gradle file that is created when you choose Gradle:

==== [src,java]

include::complete/build.gradle[]

====

=== Manual Initialization (optional)

If you want to initialize the project manually rather than use the links shown earlier, follow the steps given below:

. 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.

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

== 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:

==== [source,java]

include::complete/src/main/java/com/example/messagingredis/Receiver.java[]

====

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.

NOTE: 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 https://github.com/xetorthio/jedis[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:

==== [source,java]

include::complete/src/main/java/com/example/messagingredis/MessagingRedisApplication.java[]

====

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.

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You should see output similar to the following:

==== [source,text]

. ____ _ __ _ _ /\ / ' __ _ () __ __ _ \ \ \
( ( )__ | '_ | '| | ' / ` | \ \ \
\/ )| |)| | | | | || (| | ) ) ) ) ' || .__|| ||| |_, | / / / / =========||==============|/=//// :: 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.

NOTE: https://pivotal.io/products/redis[Redis support] is available.

== See Also

The following guides may also be helpful:

• https://spring.io/guides/gs/messaging-rabbitmq/[Messaging with RabbitMQ]
• https://spring.io/guides/gs/messaging-jms/[Messaging with JMS]
• https://spring.io/guides/gs/spring-boot/[Building an Application with Spring Boot]

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