1. Let's first create a User POJO:

public class User {

    private Long id;
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    
    public User(Long id, String name) {
        this.id = id;
        this.name = name;
    }
    
    @Override
    public String toString() {
        return "User{" + "id=" + id + ",
        name=" + name + '}';
    }
}

2. And then, we create a slow bean to return User:

public class UserBean {
    
    public User getUser(){
        try {
            TimeUnit.SECONDS.sleep(5);
            long id = new Date().getTime();
            return new User(id, "User " + id);
        } catch (InterruptedException ex) {
            long id = new Date().getTime();
            return new User(id, "Error " + id);
        }
    }
}

3. Now we create a simple Callable task to communicate with the bean:

public class AsyncTask implements Callable<User> {

    private final UserBean userBean = 
    CDI.current().select(UserBean.class).get();

    @Override
    public User call() throws Exception {
        return userBean.getUser();
    }
}

4. And finally, we create our service to schedule and write the task's result in the response:

@Stateless
@Path("asyncService")
public class AsyncService {

    @Resource(name = "LocalManagedScheduledExecutorService")
    private ManagedScheduledExecutorService executor;

    @GET
    public void asyncService(@Suspended AsyncResponse response) {

        ScheduledFuture<User> result = executor.schedule
        (new AsyncTask(), 5, TimeUnit.SECONDS);

        while (!result.isDone()) {
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException ex) {
                System.err.println(ex.getMessage());
            }
        }

        try {
            response.resume(Response.ok(result.get()).build());
        } catch (InterruptedException | ExecutionException ex) {
            System.err.println(ex.getMessage());
            response.resume(Response.status(Response.Status
           .INTERNAL_SERVER_ERROR).entity(ex.getMessage())
           .build());
        }
        
    }

}

To try this code, just deploy it to GlassFish 5 and open this URL:

http://localhost:8080/ch09-scheduled-task/asyncService