Build a Simple Group Chat with Spring Boot WebSocket – Step‑by‑Step Guide

Introduction

This article demonstrates how to build a simple real‑time group chat using Spring Boot and the Java WebSocket API.

Dependencies

<code>&lt;dependency&gt;
    &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
    &lt;artifactId&gt;spring-boot-starter-web&lt;/artifactId&gt;
    &lt;version&gt;2.2.5.RELEASE&lt;/version&gt;
&lt;/dependency&gt;
&lt;dependency&gt;
    &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
    &lt;artifactId&gt;spring-boot-starter-websocket&lt;/artifactId&gt;
    &lt;version&gt;2.2.5.RELEASE&lt;/version&gt;
&lt;/dependency&gt;</code>

Project Structure

Core Classes

WebSocketApplication

Bootstrap class with @SpringBootApplication and a main method.

<code>@SpringBootApplication
public class WebSocketApplication {
    public static void main(String[] args) {
        SpringApplication.run(WebSocketApplication.class, args);
    }
}</code>

WebSocketServer

Annotated with @Component and @ServerEndpoint, it manages client sessions, handles connection events (@OnOpen, @OnMessage, @OnClose) and broadcasts messages to all other participants.

<code>@Component
@ServerEndpoint(value = "/chat/{username}", configurator = SpringBasedConfigurator.class)
public class WebSocketServer {
    private final Map<Session, String> userSessionMap = new ConcurrentHashMap<>();

    @OnOpen
    public void onOpen(Session session, @PathParam("username") String username) {
        userSessionMap.put(session, username);
        multicastMessage(session, "欢迎" + username + "加入群聊!");
    }

    @OnMessage
    public void onMessage(Session session, String message) {
        String username = userSessionMap.get(session);
        multicastMessage(session, username + ": " + message);
    }

    @OnClose
    public void onClose(Session session) {
        String username = userSessionMap.remove(session);
        multicastMessage(session, username + "退出群聊。");
    }

    private void multicastMessage(Session session, String message) {
        for (Session userSession : userSessionMap.keySet()) {
            if (userSession == session) {
                continue;
            }
            try {
                userSession.getBasicRemote().sendText(message);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}</code>

Explanation of annotations: @ServerEndpoint defines the endpoint, @OnOpen triggers when a client connects, @PathParam extracts the username from the URL, @OnMessage processes incoming text, @OnClose runs when a client disconnects, and Session represents the WebSocket session.

SpringBasedConfigurator

Extends ServerEndpointConfig.Configurator to obtain endpoint instances from the Spring container, enabling dependency injection inside WebSocket beans.

<code>@Component
public class SpringBasedConfigurator extends ServerEndpointConfig.Configurator implements ApplicationContextAware {
    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        SpringBasedConfigurator.applicationContext = applicationContext;
    }

    @Override
    public <T> T getEndpointInstance(Class<T> clazz) throws InstantiationException {
        return applicationContext.getBean(clazz);
    }
}</code>

WebSocketConfiguration

Registers all @ServerEndpoint beans by exposing a ServerEndpointExporter bean.

<code>@Configuration
public class WebSocketConfiguration {
    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}</code>

Testing the Chat

Use an online WebSocket client (e.g., https://www.idcd.com/tool/socket) to connect to ws://localhost:8080/chat/{username} . Open two browser windows, enter different usernames, and send messages; each client receives messages from the other, confirming the group chat works.

Conclusion

The complete source code is available on GitHub at https://github.com/sanyou3/sanyou-parent.git for further exploration.