CDI freebies a.k.a built-in beans

Generally speaking,

The CDI programming model has pre-requisite 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();
	}
	}

view raw

CDIFreebieResource.java

hosted with ❤ by GitHub

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 …

Cheers!