Lesson 5
Implementing Pub/Sub for Notifications Using Lettuce in Java
Implementing Pub/Sub for Notifications

Welcome! In this unit, we will delve into implementing Pub/Sub for notifications within our Redis-based backend system project. You've already learned how to manage user data, handle transactions, and use streams for event logging using Java. Now, we'll add another powerful feature to our project: real-time notifications using Redis Pub/Sub (publish/subscribe). This will enable our system to send and receive messages instantaneously.

What You'll Build

In this unit, we'll focus on creating a simple real-time notification system using Redis Pub/Sub with Java and the Lettuce library. Specifically, we'll cover:

  1. Publishing Messages: How to send notifications.
  2. Subscribing to Channels: How to receive and handle notifications.

Here is a quick refresher on how Pub/Sub works in Redis using Java and the Lettuce library:

Java
1import io.lettuce.core.RedisClient;
2import io.lettuce.core.api.StatefulRedisConnection;
3import io.lettuce.core.api.sync.RedisCommands;
4import io.lettuce.core.pubsub.RedisPubSubAdapter;
5import io.lettuce.core.pubsub.StatefulRedisPubSubConnection;
6import io.lettuce.core.pubsub.api.sync.RedisPubSubCommands;
7
8public class Main {
9
10    public static void main(String[] args) {
11        // Connect to Redis
12        RedisClient redisClient = RedisClient.create("redis://localhost:6379/");
13        StatefulRedisConnection<String, String> publishConnection = redisClient.connect();
14        StatefulRedisPubSubConnection<String, String> pubSubConnection = redisClient.connectPubSub();
15        
16        // Subscribe to a channel
17        subscribeToChannel(pubSubConnection, "chat_room");
18
19        // Publish a message
20        publishMessage(publishConnection, "chat_room", "alice", "Hello everyone!");
21
22        // Close connections
23        publishConnection.close();
24        pubSubConnection.close();
25        redisClient.shutdown();
26    }
27
28    // Function to publish messages to a channel
29    private static void publishMessage(StatefulRedisConnection<String, String> connection, String channel, String user, String text) {
30        RedisCommands<String, String> sync = connection.sync();
31        String message = String.format("{\"user\":\"%s\", \"text\":\"%s\"}", user, text);
32        sync.publish(channel, message);
33    }
34
35    // Function to subscribe to a channel and handle incoming messages
36    private static void subscribeToChannel(StatefulRedisPubSubConnection<String, String> connection, String channel) {
37        connection.addListener(new RedisPubSubAdapter<String, String>() {
38            @Override
39            public void message(String channel, String message) {
40                System.out.println("Received message: " + message);
41            }
42        });
43
44        RedisPubSubCommands<String, String> sync = connection.sync();
45        sync.subscribe(channel);
46    }
47}

In this code, we establish a connection to Redis. The subscribeToChannel function sets up the subscription and listens for incoming messages. The publishMessage function sends a message to the specified channel. Messages are processed and printed to the console by the RedisPubSubListener, demonstrating the real-time notification system in action.

Exciting, isn’t it? Now, it's time to put this into practice. Let's implement the complete code to build our real-time notification system.

Happy coding!

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