Get maximum table value (JPA) with Java 8

Question

I have a method in my DAO class that returns a general list of the table:

public List<ObjetoRisco> findAll() {
    return manager.createQuery("select o from ObjetoRisco o", ObjetoRisco.class).getResultList();
}

In my class Controller, I’m having a hard time filtering out the maximum value of the ID column using the Java 8 API. The closest I came to the desired result was this way:

Optional<Integer> maxId = objetoRiscoDao.findAll().stream().map(ObjetoRisco::getId).max(Integer::compare);
modelAndView.addObject("maxId", maxId);

But when I call on my JSP ${maxId}, I receive in response Optional[270]. In fact the 270 is the last id, but I’m not getting it as whole so I can manipulate it, like,: ${maxId + 1}.

Answer 1

Simply "uncouple" the content of Optional:

Optional<Integer> maxId = objetoRiscoDao.findAll().stream().map(ObjetoRisco::getId).max(Integer::compare);
modelAndView.addObject("maxId", maxId.get());

Or rather:

Integer maxId = objetoRiscoDao.findAll().stream().map(Integer::new).max(Integer::compare).orElse(1); // Retorna valor padrão

Or:

Integer maxId = objetoRiscoDao.findAll().stream().map(Integer::new).max(Integer::compare).orElseGet(() -> 1 + 2); // Retorna algum cálculo ou resultado de função

Or else:

Integer maxId = objetoRiscoDao.findAll().stream().map(Integer::new).max(Integer::compare).orElseThrow(() -> new RuntimeException("Não existe máximo")); // Lança exceção caso deva existir máximo

Answer 2

I was able to solve using the resource below:

Integer max = maxId.hashCode();

Thank you!

Answer 3

Integer contained in Optional failed to be extracted:

modelAndView.addObject("maxId", maxId.get());

However worth remembers that this Optional can contain a null internally, so requires a treatment or check before extracting it.