The CDI programming model has prerequisite requirements for beans which are lucky enough to leverage its services (DI, contextual state management etc.). This ranges from typical Java EE Managed Beans, EJB (session) beans etc. (I’ll leave the details for another post).

But the Good Thing is That

...it also provides some freebies i.e. beans which are available for injection by default

• HttpSession
• HttpServletRequest
• ServletContext
• UserTransaction
• Principal

To be Noted

• One can user either @Resource or the more obvious @Inject annotation to trigger injection
• The @Default qualifier is applicable to injected instances of these beans

@Stateless
@TransactionManagement(TransactionManagementType.BEAN)
@Path("cdi/freebies")
public class CDIFreebieResource {

    @Inject
    UserTransaction uTx;
    @Inject
    Principal actor;
    @Inject
    HttpSession httpSession;
    @Inject
    HttpServletRequest httpSR;
    @Inject
    ServletContext sCtx;

    @GET
    public String get() throws Exception{
        return 
        "User Tx status: " + uTx.getStatus() + "\n" +
        "Principal: " + actor.getName() + "\n" +
        "HTTP Session ID: " + httpSession.getId() + "\n" +
        "HTTP Method: " + httpSR.getMethod() + "\n" + 
        "Context Path: " + sCtx.getContextPath();
    }
}

Where can I Inject These Beans ?

Well, standard rules (defined by the CDI specification) apply here. I would recommend looking into the official Java EE Platform specification document (section EE 5.2.5, Table EE.5-1) which details this clearly. Here is a snapshot – Java EE managed beans, CDI managed beans, EJB, Servlet spec components, Web Socket endpoints, JSF managed beans etc.

Go on, check out the freebies …