Redis PubSub (#1151)

* Redis PubSub

* Redis PubSub

* Redis PubSub - review comments incorporated

* Redis PubSub - review comments incorporated

* Redis PubSub - review comments incorporated

* Redis PubSub - review comments incorporated

* Redis PubSub - review comments incorporated

Author: abh1navv

kotlin-libraries-data/pom.xml

@@ -95,6 +95,16 @@
             <version>${moshi.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.github.codemonstur</groupId>
+            <artifactId>embedded-redis</artifactId>
+            <version>${embedded-redis.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>io.lettuce</groupId>
+            <artifactId>lettuce-core</artifactId>
+            <version>${lettuce-core.version}</version>
+        </dependency>
     </dependencies>
 
     <build>
@@ -161,6 +171,9 @@
         <retrofit.version>2.9.0</retrofit.version>
         <wiremock-jre8.version>2.35.1</wiremock-jre8.version>
         <moshi.version>1.15.1</moshi.version>
+        <kotlinx-coroutines.version>1.7.1</kotlinx-coroutines.version>
+        <embedded-redis.version>1.4.3</embedded-redis.version>
+        <lettuce-core.version>6.5.0.RELEASE</lettuce-core.version>
     </properties>
 
 </project>

kotlin-libraries-data/src/main/kotlin/com/baeldung/redispubsub/Message.kt

@@ -0,0 +1,3 @@
+package com.baeldung.redispubsub
+
+data class Message(val content: String)

kotlin-libraries-data/src/main/kotlin/com/baeldung/redispubsub/MessageListener.kt

@@ -0,0 +1,17 @@
+package com.baeldung.redispubsub
+
+import io.lettuce.core.pubsub.RedisPubSubAdapter
+import java.util.concurrent.CountDownLatch
+
+class MessageListener : RedisPubSubAdapter<String, String>() {
+
+    var latch: CountDownLatch = CountDownLatch(1)
+
+    var messagesReceived: List<String> = emptyList()
+    override fun message(channel: String?, message: String?) {
+        println("Received message: $message from channel: $channel")
+        messagesReceived = messagesReceived.plus(message!!)
+        latch.countDown()
+    }
+
+}

kotlin-libraries-data/src/main/kotlin/com/baeldung/redispubsub/RedisConnectionManager.kt

@@ -0,0 +1,26 @@
+package com.baeldung.redispubsub
+
+import io.lettuce.core.RedisClient
+import io.lettuce.core.api.StatefulRedisConnection
+import io.lettuce.core.api.sync.RedisCommands
+import io.lettuce.core.pubsub.api.async.RedisPubSubAsyncCommands
+
+object RedisConnectionManager: AutoCloseable {
+    private val redisClient: RedisClient = RedisClient.create("redis://localhost:6379")
+    private val connection: StatefulRedisConnection<String, String> = redisClient.connect()
+
+    override fun close() {
+        connection.close()
+        redisClient.shutdown()
+    }
+
+    fun redisSyncCommands(): RedisCommands<String, String>? {
+        return connection.sync()
+    }
+
+    fun redisPubSubAsyncCommands(messageListener: MessageListener): RedisPubSubAsyncCommands<String, String> {
+        val pubSubConnection = redisClient.connectPubSub()
+        pubSubConnection.addListener(messageListener)
+        return pubSubConnection.async()
+    }
+}

kotlin-libraries-data/src/main/kotlin/com/baeldung/redispubsub/RedisPublisher.kt

@@ -0,0 +1,9 @@
+package com.baeldung.redispubsub
+
+class RedisPublisher {
+
+    fun publishMessage(channel: String, message: Message) {
+        RedisConnectionManager.redisSyncCommands()?.publish(channel, message.content)
+        println("Message published: $message")
+    }
+}

kotlin-libraries-data/src/main/kotlin/com/baeldung/redispubsub/RedisSubscriber.kt

@@ -0,0 +1,9 @@
+package com.baeldung.redispubsub
+
+class RedisSubscriber(private val messageListener: MessageListener) {
+
+    fun subscribeToChannel(channel: String) {
+        RedisConnectionManager.redisPubSubAsyncCommands(messageListener).subscribe(channel)
+    }
+
+}

kotlin-libraries-data/src/test/kotlin/com/baeldung/redispubsub/RedisSubscriberUnitTest.kt

@@ -0,0 +1,41 @@
+package com.baeldung.redispubsub
+
+import org.junit.jupiter.api.AfterAll
+import org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.BeforeAll
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.TestInstance
+import redis.embedded.RedisServer
+import java.util.concurrent.TimeUnit
+
+@TestInstance(TestInstance.Lifecycle.PER_CLASS)
+class RedisSubscriberUnitTest {
+
+    val messageListener = MessageListener()
+    val redisSubscriber = RedisSubscriber(messageListener)
+    val redisPublisher = RedisPublisher()
+    val channel = "channel"
+    val message = Message("Hello, Redis!")
+
+    val redisServer = RedisServer(6379)
+
+    @BeforeAll
+    fun setUp() {
+        redisServer.start()
+    }
+
+    @AfterAll
+    fun tearDown() {
+        RedisConnectionManager.close()
+        redisServer.stop()
+    }
+
+    @Test
+    fun givenMessageListener_whenMessagePublished_thenMessageReceived() {
+        redisSubscriber.subscribeToChannel(channel)
+        redisPublisher.publishMessage(channel, message)
+        messageListener.latch.await(500, TimeUnit.MILLISECONDS)
+        assertEquals(message.content, messageListener.messagesReceived.get(0))
+    }
+
+}