This guide walks you through the process of using Spring Data Redis to publish and subscribe to messages sent with Redis.
You will build an application that uses StringRedisTemplate to publish a string message
and has a POJO subscribe for the message by using MessageListenerAdapter.
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Note
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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. |
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 redisOnce you unpack Redis, you can launch it with its default settings by running the following command:
redis-serverYou 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 6379For all Spring applications, you should start with the Spring Initializr. The Initializr offers a fast way to pull in all the dependencies you need for an application and does a lot of the set up for you. This example needs only the Spring for Redis dependency. The following image shows the Initializr set up for this sample project:
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Note
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The preceding image shows the Initializr with Maven chosen as the build tool. You
can also use Gradle. It also shows values of com.example and messaging-redis as the
Group and Artifact, respectively. You will use those values throughout the rest of this
sample.
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The following listing shows the pom.xml file that is created when you choose Maven:
link:complete/pom.xml[role=include]
The following listing shows the build.gradle file that is created when you choose Gradle:
link:complete/build.gradle[role=include]
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:
link:complete/src/main/java/com/example/messagingredis/Receiver.java[role=include]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.
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Note
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For demonstration purposes, the receiver is counting the messages received. That way, it can signal when it has received a message. |
Spring Data Redis provides all the components you need to send and receive messages with Redis. Specifically, you need to configure:
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A connection factory
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A message listener container
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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:
link:complete/src/main/java/com/example/messagingredis/MessagingRedisApplication.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 (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.
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!>Congratulations! You have just developed a publish-and-subscribe application with Spring and Redis.
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Note
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Redis support is available. |
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