Redis Caching & Messaging (Pub/Sub, Streams) · レッスン

リアルタイムチャットの設計

メッセージ配信に Pub/Sub を使用する、基本的なリアルタイムチャットアプリケーションを実装します。

「リアルタイムチャットの設計」はCoddyKit上の無料Redis Caching & Messaging (Pub/Sub, Streams)レッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはRedis Caching & Messaging (Pub/Sub, Streams)学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 Redis Caching & Messaging (Pub/Sub, Streams)コースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Real-time Chat with Pub/Sub

Imagine building a chat application where messages appear instantly! This is where Redis Pub/Sub shines. It's perfect for real-time communication without constant 'checking for new messages'.

In this lesson, you'll learn how to design a basic chat system using Redis Publish/Subscribe, turning chat rooms into channels and messages into published events.

Chat Rooms as Redis Channels

The core idea for a chat application with Pub/Sub is simple: each chat room corresponds to a unique Redis Channel.

When a user wants to join a chat room (e.g., 'general' or 'support'), their client application will subscribe to the corresponding Redis channel.
When a user sends a message in that room, their client will publish the message to that specific channel.

Subscribing to Join a Room

To 'join' a chat room, a client needs to start listening for messages on its channel. This is done by subscribing. Once subscribed, the client will receive all messages published to that channel.

Below is a simplified Java example using a Redis client library (like Jedis) to subscribe to a channel named chat:general.

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPubSub;

public class ChatSubscriber {
  public static void main(String[] args) {
    try (Jedis jedis = new Jedis("localhost")) {
      System.out.println("Subscribing to chat:general...");
      jedis.subscribe(new JedisPubSub() {
        @Override
        public void onMessage(String channel, String message) {
          System.out.println("Received on " + channel + ": " + message);
        }
      }, "chat:general");
    } catch (Exception e) {
      System.err.println("Error: " + e.getMessage());
    }
  }
}

Publishing to Send Messages

When a user types a message and hits 'send', their client application will publish that message to the channel corresponding to the current chat room. All clients currently subscribed to that channel will immediately receive the message.

This Java example shows how a client would publish a message to the chat:general channel.

import redis.clients.jedis.Jedis;

public class ChatPublisher {
  public static void main(String[] args) {
    try (Jedis jedis = new Jedis("localhost")) {
      String message = "Hello, everyone!";
      jedis.publish("chat:general", message);
      System.out.println("Published: '" + message + "'");
    } catch (Exception e) {
      System.err.println("Error: " + e.getMessage());
    }
  }
}

Demo: User A Listens

Let's see this in action! Run this program in one terminal. It simulates User A joining the chat:general room and waiting for messages. It will block and print any message it receives.

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPubSub;

public class UserA {
  public static void main(String[] args) {
    try (Jedis jedis = new Jedis("localhost")) {
      System.out.println("User A is listening on chat:general...");
      jedis.subscribe(new JedisPubSub() {
        @Override
        public void onMessage(String channel, String message) {
          System.out.println("User A received: " + message);
        }
      }, "chat:general");
    } catch (Exception e) {
      System.err.println("Error: " + e.getMessage());
    }
  }
}

Demo: User B Sends

Now, open a separate terminal and run this program. It simulates User B sending a message to the chat:general room. Watch User A's terminal – it should instantly receive User B's message!

import redis.clients.jedis.Jedis;

public class UserB {
  public static void main(String[] args) {
    try (Jedis jedis = new Jedis("localhost")) {
      String message = "Hey User A, are you there?";
      jedis.publish("chat:general", message);
      System.out.println("User B published: '" + message + "'");
    } catch (Exception e) {
      System.err.println("Error: " + e.getMessage());
    }
  }
}

Designing Your Chat Message

A simple string message isn't usually enough for a chat application. You'll want to include more context. A common approach is to serialize chat message data into a format like JSON before publishing it.

Consider including:

sender: The username or ID of who sent the message.
timestamp: When the message was sent (for ordering).
text: The actual content of the message.
roomId: (Optional) The channel/room ID, useful for client-side processing.

Handling Multiple Chat Rooms

To support many different chat rooms (e.g., 'general', 'private:alice-bob', 'developers'), you simply use different channel names.

Each room gets a unique channel name (e.g., chat:general, chat:support).
Clients subscribe only to the channels of the rooms they are active in.
When a user switches rooms, their client unsubscribes from the old channel and subscribes to the new one.

Pub/Sub's Non-Persistent Nature

It's crucial to remember that Redis Pub/Sub is a fire-and-forget system. Messages are delivered to all currently active subscribers and then disappear.

If a user is offline or not subscribed when a message is published, they will not receive that message when they come back online.
For persistent chat history or messages to offline users, you would need to combine Pub/Sub with other Redis data structures (like Lists or Streams) or a separate database.

Chat Design Quiz

You're building a chat app with Redis Pub/Sub. Users join rooms by subscribing to channels. If User A is subscribed to chat:tech and User B publishes a message to chat:random, what happens?

Recap: Real-time Chat Design

You've learned the basics of designing a real-time chat application using Redis Pub/Sub:

Each chat room maps to a unique Redis channel.
Users subscribe to a channel to join a room and receive messages.
Users publish messages to a channel to send them to all subscribers.
Messages should be structured (e.g., JSON) to include sender, timestamp, and content.
Remember that Pub/Sub is non-persistent; messages are gone once delivered.

This foundation allows for highly responsive chat experiences!

よくある質問

「リアルタイムチャットの設計」レッスンは無料ですか？

はい。「リアルタイムチャットの設計」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、Redis Caching & Messaging (Pub/Sub, Streams)コースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 Redis Caching & Messaging (Pub/Sub, Streams)コースには全4レッスンが含まれています。

「リアルタイムチャットの設計」で何を学びますか？

メッセージ配信に Pub/Sub を使用する、基本的なリアルタイムチャットアプリケーションを実装します。ブラウザで直接実行するハンズオンコードでRedis Caching & Messaging (Pub/Sub, Streams)を演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

Redis Caching & Messaging (Pub/Sub, Streams)を始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのRedis Caching & Messaging (Pub/Sub, Streams)は初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「リアルタイムチャットの設計」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このRedis Caching & Messaging (Pub/Sub, Streams)レッスンでコードを書いて実行できますか？

はい。すべてのRedis Caching & Messaging (Pub/Sub, Streams)レッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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