How to Publish and Subscribe to Redis Using Lettuce

The source code for what follows can be found on Github.

Subscribing to topics in redis allows for a fanout behavior, where any number of subscribers can be notified of a message from a publisher.

With the cli, you can simply run:

redis-cli subscribe some-channel
Reading messages... (press Ctrl-C to quit)
1) "subscribe"
2) "some-channel"
3) (integer) 1

Then, in another terminal, we can:

redis-cli publish some-channel some-message
(integer) 1

And we will see in the original terminal where we're still subscribed:

1) "message"
2) "some-channel"
3) "some-message"

In java using lettuce, the process is pretty similar, but subscribing is a little wonky.

Publish/Subscribe with Lettuce

For a fast feedback loop, you can refer to either using embedded redis to test lettuce or using a redis test container to test lettuce as a starting point. Once that's in place, subscribing and publishing looks like this:

    @Test
    public void publishAndSubscribe() throws Exception {
        StatefulRedisPubSubConnection<String, String> pubSubConnection =
                redisClient.connectPubSub();

        AtomicBoolean messageReceived = new AtomicBoolean(false);
        RedisPubSubReactiveCommands<String, String> reactivePubSubCommands = pubSubConnection.reactive();
        reactivePubSubCommands.subscribe("some-channel").subscribe();

        reactivePubSubCommands.observeChannels()
                .doOnNext(stringStringChannelMessage -> messageReceived.set(true))
                .subscribe();

        Thread.sleep(25);

        redisClient.connectPubSub()
                .reactive()
                .publish("some-channel", "some-message")
                .subscribe();

        Thread.sleep(25);

        Assertions.assertTrue(messageReceived.get());
    }

The gist of the code is that we publish to the channel after we subscribe, and verify that we actually received a message by asserting that an AtomicBoolean was flipped to true. This test passes.