title: How to get all active sessions in Spring 5 WebSocket API?
body: <p>I code WebSocket application with help classical Spring 5 WebSocket API, i.e. without using of SockJS and STOMP.
  I have a problem to get all active http-sessions.
  I can get one current session, but how to get all active sessions?
  If I would use a classical Java API(JSR356), I would use a method: session.getOpenSessions() to get all opened sessions.
  But I can't find anything like this method in Spring 5 WebSocket API.
  How to get all active sessions?</p>
  
  <pre><code>//Configuration of WebSocket.
  
  @Configuration
  @EnableWebSocket
  public class WebSocketConfig implements 
  WebSocketConfigurer {
  
  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    //Map endpoint URL to handler's method.
    //Add interceptor of HTTP-handshake to copy HTTP-session's attributes to WebSocket-session's attributes.
    registry.addHandler(getWsEndpoint(), "/endpoint").addInterceptors(new HttpSessionHandshakeInterceptor());
  }
  
  @Bean
  public WebSocketHandler getWsEndpoint() {
      return new WsEndpoint();
  }
  }
  </code></pre>
  
  <p>My WebSocket endpoint:</p>
  
  <pre><code>// WebSocket endpoint class. 
  
  public class WsEndpoint extends TextWebSocketHandler {
  
   public WsEndpoint(){}
  
   public WebSocketMessage&lt;String&gt; wsMsg;                      
  
    // This method will be called after successful websocket connection.
    @Override
    public void afterConnectionEstablished(WebSocketSession session)                                     
     throws java.lang.Exception {
  
       wsMsg = new TextMessage(new String("Connection ok!"));        
     session.sendMessage(wsMsg);  
    }
  
      // This method is called if message was recieved. 
      @Override
      public void handleTextMessage(WebSocketSession session, TextMessage message) throws IOException {       
  
       wsMsg = new TextMessage(new String("Message recieved!")); 
       session.sendMessage(wsMsg);
      }
  }
  </code></pre>