Why is HTTPServletRequest injectable via CDI but HTTPServletResponse isn't?

Question

This question took off because I read Arjan Tijms blogpost about JSF 2.3 . There, he list all JSF artifacts which can be injected via CDI. Although HttpServletRequest is mentioned, HttpServletResponse doesn't appear on the said list which I didn't believe at first.

To try things out, I setup a simple Server (JavaEE8, Wildfy22):

• @Inject private HttpServletRequest req; works just fine
• @Inject private HttpServletResponse res; throws DeploymentException: WELD-001408: Unsatisfied dependencies for type HttpServletResponse

I don't see why HttpServletResponse should not be injectable. After all, the goal was to replace convulent method chains by a concise injection. In case of HttpServletRequest , FacesContext.getCurrentInstance().getExternalContext().getRequest(); can now be shortened to the above injection.

Well, in case of HttpServletResponse , there is no injection candidate to replace FacesContext.getCurrentInstance().getExternalContext().getResponse(); as shown above.

Summarized: Why is HttpServletRequest injectable via CDI but HttpServletResponse isn't?

Answer 1

There's not a single good answer here.

To start with, HttpServletRequest is produced by CDI, not Faces. As for HttpServletResponse I'm not sure why it wasn't original included in CDI, but I do know that all the Servlet artefacts should originally not have been provided by CDI.

Instead, CDI should have asked Servlet to provide "producers" for them (technically, build-in beans). Jakarta Transactions (JTA back then) did something similar)

Currently, CDI doesn't want to enhance or expand the Servlet artefacts, and with good reason. CDI is focussing on its core bean model and injection.

However, in Servlet there is a huge misunderstanding of what it means to provide producers. At least one person in Servlet thinks it's about providing integration points, or about Servlet having to become completely CDI based, or about Jetty having to support all 10 CDI implementations out there (there are only 2, but that aside).

This discussion has been going on for at least 8 years. Issues have been opened and closed again.

I'm a Servlet member myself so I hope I have some influence, but still have not been able to get this resolved.

We could alternatively have Faces provide HttpServletResponse , but Faces also does not own that type, and it would likely only contribute to the confusion.

Answer 2

As said already injecting the HttpServletResponse is not supported by CDI by default. The Servlet module from Apache DeltaSpike however allows for injectable servlet objects such as the HttpServletResponse . So there is no need for writing a custom CDI Producer or @Produces method in order to inject the HttpServletResponse via CDI.