Why can't I Init attribute in Managed Bean constructor?

Question

I have a Managed Bean:

public class CategoriaManagedBean {
  @EJB
  private CategoriaBeanLocal categoriaBean;
  private Categoria categoria;
  private List<Categoria> menu;
}

In my constructor I try:

public CategoriaManagedBean() {
  menu = categoriaBean.findByIdCategoriaPadre(0);
}

But I get a error "Cannot create the instance of the class", why can't I initialize the attribute in the constructor?

I fix the problem with:

@PostConstruct
public void init() {
  menu = categoriaBean.findByIdCategoriaPadre(0);
}

But I want to know the reason and if I am doing well with @PostConstruct

Greetings.

Answer 1

Using @PostConstruct is the correct approach.

EJBs are injected after the constructor is invoked on a ManagedBean.

That's why there is a @PostConstruct annotation.

Here's the first line from the documentation:

The PostConstruct annotation is used on a method that needs to be executed after dependency injection is done to perform any initialization.