I discovered that using:

@Autowired
private NewGradeHandler newGradeHandler; 

I was creating a new instance without the previous connections. So, if this happens to you. in the method you want to consume your WebSocket do:

1. declare:

    @Autowired
    private ApplicationContext applicationContext; // Inyecta el ApplicationContext
   

2. Use this instance, make sure the String in the getBean method has the sam name as your class:

NewGradeHandler newGradeHandler = applicationContext.getBean("NewGradeHandler",NewGradeHandler.class);