How it works...

Let's first check the getUser method from the session bean:

    @Asynchronous
    public Future<User< getUser(){
        long id = new Date().getTime();
        User user = new User(id, "User " + id);
        return new AsyncResult(user);
    }

Once we use the @Asynchronous annotation, we have to turn its returning value into a Future instance of something (in our case, User).

We have also created a void method to show you how to create a non-blocking code with session beans:

    @Asynchronous
    public void doSomeSlowStuff(User user){
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException ex) {
            System.err.println(ex.getMessage());
        }
    }

Finally, we create our calling endpoint:

    @GET
    public void asyncService(@Suspended AsyncResponse response){
        try {
            Future<User< result = userBean.getUser();
            
            while(!result.isDone()){
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException ex) {
                    System.err.println(ex.getMessage());
                }
            }
            
            response.resume(Response.ok(result.get()).build());
        } catch (InterruptedException | ExecutionException ex) {
            System.err.println(ex.getMessage());
        }
    }

As getUser returns Future, we can work with an async status check. Once this is done, we write the results in the response (also asynchronous).