如果使用Spring + SockJS + STOMP，websocket消息会被缓存吗？如果没有，如何检测网络断开？

// 客户端代码
var heartbeatInterval = 10000; // 心跳间隔时间，单位为毫秒
var heartbeatTimer = null;

function sendHeartbeat() {
    stompClient.send("/app/heartbeat");
}

function startHeartbeat() {
    heartbeatTimer = setInterval(sendHeartbeat, heartbeatInterval);
}

function stopHeartbeat() {
    clearInterval(heartbeatTimer);
}

// 在连接成功后启动心跳
stompClient.connect({}, function(frame) {
    console.log('Connected: ' + frame);
    startHeartbeat();
});

// 在接收到消息时重置心跳计时器
stompClient.subscribe('/topic/messages', function(message) {
    console.log('Received: ' + message.body);
    // 重置心跳计时器
    clearInterval(heartbeatTimer);
    startHeartbeat();
});

// 服务器端代码
@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
    
    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/topic");
        config.setApplicationDestinationPrefixes("/app");
    }
    
    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/websocket").withSockJS();
    }
    
    @Override
    public void configureClientInboundChannel(ChannelRegistration registration) {
        registration.setInterceptors(new HeartbeatInterceptor());
    }
}

public class HeartbeatInterceptor extends ChannelInterceptorAdapter {
    
    private static final long HEARTBEAT_TIMEOUT = 20000; // 心跳超时时间，单位为毫秒
    
    @Override
    public Message<?> preSend(Message<?> message, MessageChannel channel) {
        // 处理心跳消息
        StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
        if (accessor.getCommand() == StompCommand.SEND && "/app/heartbeat".equals(accessor.getDestination())) {
            // 不做处理，直接返回
            return message;
        }
        
        // 判断是否超时
        long lastActiveTime = (long) accessor.getSessionAttributes().get("lastActiveTime");
        if (System.currentTimeMillis() - lastActiveTime > HEARTBEAT_TIMEOUT) {
            // 触发网络断开的逻辑
            System.out.println("Network Disconnected!");
        }
        
        // 更新最后活动时间
        accessor.getSessionAttributes().put("lastActiveTime", System.currentTimeMillis());
        
        return message;
    }
    
    @Override
    public void postSend(Message<?> message, MessageChannel channel, boolean sent) {
        // 处理发送的消息
        StompHeaderAccessor accessor = StompHeaderAccessor.wrap(message);
        if (StompCommand.CONNECTED.equals(accessor.getCommand())) {
            // 初始化最后活动时间
            accessor.getSessionAttributes().put("lastActiveTime", System.currentTimeMillis());
        }
    }
}