How to do it...

You need to perform the following steps to complete this recipe:

1. Let's create a User class. This will be our cached object:

public class User {
    
    private String name;
    private String email;
  
    //DO NOT FORGET TO IMPLEMENT THE GETTERS AND SETTERS
}

2. Next, create a singleton that will hold our user list cache:

@Singleton
@Startup
public class UserCacheBean {

    protected Queue<User> cache = null;
    
    @PersistenceContext
    private EntityManager em;

    public UserCacheBean() {
    }

    protected void loadCache() {
        List<User> list = em.createQuery("SELECT u FROM USER 
                                         as u").getResultList();

        list.forEach((user) -> {
            cache.add(user);
        });
    }

    @Lock(LockType.READ)
    public List<User> get() {
        return cache.stream().collect(Collectors.toList());
    }

    @PostConstruct
    protected void init() {
        cache = new ConcurrentLinkedQueue<>();
        loadCache();
    }
}

Now, let's see how this recipe works.