一、引入spring-websocket依赖

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<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-websocket</artifactId>
</dependency>

二、开启websocket支持

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/**
 * 开启websocket的支持
 */
@Configuration
public class WebsocketConfig {

    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}

三、websocket工具类

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/**
 * websocket工具类
 */
@Slf4j
public class WebsocketUtil {

    private WebsocketUtil() {
    }

    /**
     * 服务端存放客户端对应的session对象
     * key:clientId value:session
     */
    public static final Map<String, Session> WEBSOCKET_CLIENT_SESSION_MAP = Maps.newConcurrentMap();

    /**
     * 服务端发送消息给所有客户端
     *
     * @param message
     */
    public static void sendMessageToAllClient(String message) {
        if (WEBSOCKET_CLIENT_SESSION_MAP.isEmpty()) {
            log.info("当前无连接的客户端, 消息忽略推送.");
            return;
        }
        WEBSOCKET_CLIENT_SESSION_MAP.forEach((sessionId, session) -> {
            try {
                session.getBasicRemote().sendText(message);
            } catch (Exception e) {
                log.error("服务端向客户端[{}]发送消息异常.", sessionId, e);
            }
        });
    }
}

四、websocket服务端

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/**
 * websocket服务端
 */
@Slf4j
@Component
@ServerEndpoint("/websocket")
public class WebsocketServer {

    private String sessionId;

    /**
     * websocket建立连接
     *
     * @param session
     * @throws IOException
     */
    @OnOpen
    public void onOpen(Session session) throws IOException {
        this.sessionId = session.getId();

        if (WebsocketUtil.WEBSOCKET_CLIENT_SESSION_MAP.containsKey(this.sessionId)) {
            WebsocketUtil.WEBSOCKET_CLIENT_SESSION_MAP.remove(this.sessionId).close();
        }

        WebsocketUtil.WEBSOCKET_CLIENT_SESSION_MAP.put(this.sessionId, session);

        log.info("客户端[{}]建立websocket连接.", this.sessionId);
    }

    /**
     * 关闭socket连接
     *
     * @param session
     */
    @OnClose
    public void onClose(Session session) {
        if (WebsocketUtil.WEBSOCKET_CLIENT_SESSION_MAP.containsKey(session.getId())) {
            WebsocketUtil.WEBSOCKET_CLIENT_SESSION_MAP.remove(session.getId());
            log.info("客户端[{}]断开websocket连接.", session.getId());
        }
    }

    /**
     * 接收到消息
     *
     * @param message
     */
    @OnMessage
    public void OnMessage(String message) {
        log.info("接收到客户端{}发送的消息:[{}].", this.sessionId, message);
    }

    /**
     * 连接错误
     *
     * @param session
     * @param error
     */
    @OnError
    public void OnError(Session session, Throwable error) {
        log.error("websocket连接错误,", error);
    }
}

五、测试

推荐使用Chrome插件–Simple Web Socket Client