The Java EE 6 Tutorial, Volume I

Obtaining a CriteriaBuilder Instance in RequestBean

The CrtiteriaBuilder interface defines methods to create criteria query objects, create expressions for modifying those query objects. RequestBean creates an instance of CriteriaBuilder by using a @PostConstruct method, init.

private EntityManager em;
private CriteriaBuilder cb;

private void init() {
  cb = em.getCriteriaBuilder();

The EntityManager instance is injected at runtime, and then that EntityManager object is used to create the CriteriaBuilder instance by calling getCriteriaBuilder. The CriteriaBuilder instance is created in a @PostConstruct method to ensure that the EntityManager instance has been injected by the enterprise bean container.