Spring Websocket : send notification to subscribed client without any request-CodePudding

Im writing back front java code spring 2.2.5. The front is connected to the back via a websocket. I want to send notifications to the client without request sent by client only connection and subscrition events are received by the server. I tried some solotion based on SimpMessagingTemplate but when i'm trying to send back to the client using this interface (without request) the data is null pointer.

Controller code :

private SimpMessagingTemplate messagingTemplate;
@Autowired
public void WebSocketController(SimpMessagingTemplate messagingTemplate) {
    this.messagingTemplate = messagingTemplate;
}

@RequestMapping(value = "/post/message", method = RequestMethod.POST)
public void PostMessage(@PathVariable String message) {
    this.messagingTemplate.convertAndSend("/topic/myDest", message);
}

With the following config code i intercept connect and subscribe events, is there a way to save client parameter in order to send back notifications to it.

@Override
public void configureClientInboundChannel(ChannelRegistration registration){
    registration.interceptors(new ChannelInterceptor() {
        @Override
        public Message<?> preSend(Message<?> message, MessageChannel channel) {
            StompHeaderAccessor accessor = MessageHeaderAccessor.getAccessor(message, StompHeaderAccessor.class);

            if(StompCommand.CONNECT.equals(accessor.getCommand())){
                String sessionId = accessor.getSessionId();
                System.out.println("Connect "   sessionId);
            } else if(StompCommand.SUBSCRIBE.equals(accessor.getCommand())){
                System.out.println("Subscribe ");
            } else if(StompCommand.SEND.equals(accessor.getCommand())){
                System.out.println("Send message " );
            } else if(StompCommand.DISCONNECT.equals(accessor.getCommand())){
                System.out.println("Exit ");
            } else {
            }
            return message;
        }
    });
}

CodePudding user response：

I finally find the solution: In my previous PreSend interceptor, i can save all subscribed clients :

xxxx.Channels.add(channel);

In xxx class : Channels is defined as :

public final ArrayList<MessageChannel>  Channels = new ArrayList<MessageChannel>();

In Post function i created a SimpMessagingTemplate instance for each channel :

for (int i = 0; i < Channels.size(); i  ) {
  MessageChannel channel = Channels.get(i);
  SimpMessagingTemplate messagingTemplate = new SimpMessagingTemplate(channel);
  messagingTemplate.convertAndSend("/topic/myDest", data.toString().getBytes());
}

And the message is correctly sent.