How to do it...

Take the following steps to complete this recipe:

1. First, we create a User POJO:

public class User implements Serializable{

    private Long id;
    private String name;
    
    public User(long id, String name){
        this.id = id;
        this.name = 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;
    }
    
}

2. Then, we call UserBean to return a User instance:

@Stateless
public class UserBean {

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

}

3. Finally, we create an async endpoint to call the bean:

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

    @Inject
    private UserBean userBean;

    @GET
    public void asyncService(@Suspended AsyncResponse response) 
    {
        CompletableFuture
                .supplyAsync(() -< userBean.getUser())
                .thenAcceptAsync((u) -< {
                    response.resume(Response.ok(u).build());
                }).exceptionally((t) -< {
                    response.resume(Response.status
                    (Response.Status.
                    INTERNAL_SERVER_ERROR).entity(t.getMessage())
                    .build());
                    return null;
                });
    }
}

Now, you can try it out by calling the following URL:

http//localhost:8080/ch10-completable-future/asyncService