Injectable configuration

[Emily-Jiang]

Do we want to support Injectable configuration in this spec?

[radcortez]

No. It should be in the scope of CDI, not here.

[hantsy]

No, CDI is the kernel of Jakarta EE specs now, other specs should adapt CDI automatically.

Like the Spring IOC, all spring components are based on it.

[dmlloyd]

A qualified "yes" - injection as @radcortez points out is the purview of CDI, not us. However, it should be possible for an application to inject their configuration object (see my comments on the "Programmatic API" thread) by its type, which should uniquely identify the application configuration. This specification should state that compliant implementations of this specification which also implement the CDI specification are required to facilitate this in an implementation-specific manner.

[ljnelson]

The way I see it:

• CDI is (definitionally) a Jakarta Dependency Injection implementation. (Spring is another; HK2 is still another; I think Guice is another; I'm sure there are many others.)
• Jakarta Dependency Injection is a "consumer-only" specification, i.e. it does not really speak about how "injectors" work, other than the bare minimum required, only about how injection points work, regardless of how an implementation satisfies those injection points
• If we say that Jakarta Config in most (but, very importantly, not all) situations depends on Jakarta Dependency Injection, doesn't this dodge the circularity? That gives you injection points, jakarta.inject.Inject, the non-proxied Singleton scope, the Provider construct, and qualifiers. There's probably not a whole lot more that we would need. Maybe that's a partial way out?

(Note: I deliberately say "most…situations" and not "all…situations" because there can be very important restrictions on injection imposed by Jakarta Dependency Injection implementations (like CDI). For example, within a CDI portable extension, you cannot @Inject anything, even though CDI is a Jakarta Dependency Injection implementation, because the container is still coming up. I'm guessing there are similar restrictions in other Jakarta Dependency Injection implementations: I would imagine, though I'm no expert, that, say, in Guice you probably can't inject things inside injectors either. That's another discussion related, perhaps, but not identical to, #110, and should not be addressed directly here.)

[dmlloyd]

I don't see any reason to specify this in any greater complexity than:

Conforming implementations of Jakarta Config which are provide a conforming implementation of Jakarta CDI must allow configuration root objects to be injected into applications as beans. (plus any necessary additional information about qualifiers etc.)

In particular we do not need to establish a dependency either way, nor do we need to specify any additional requirements on CDI itself.

[ljnelson]

If all that's required is injection, don't you think we could replace "CDI" with "Jakarta Dependency Injection" instead? Might be even simpler.

[dmlloyd]

If that is the proper name of the specification or a normative term then yes.

[ljnelson]

For clarity (and the benefit of others): Jakarta Dependency Injection is its own spec. CDI is an extension of it.

(Weirdly the CDI page calls itself Jakarta Contexts and Dependency Injection, Jakarta Context Dependency Injection (!) and Jakarta Contexts Dependency Injection (!). Yikes. I think the first one is the proper name for it.)

[ljnelson]

I see configuration as a spectrum:

(In terms of the spectrum, injecting configuration falls in the yellow/left end of the spectrum.)

I agree that injection of configuration (where that term is deliberately left undefined here) should be supported where possible.

I agree that CDI should be the mechanism by which injection is implemented wherever possible.

As David notes correctly, there are also cases where injection cannot be supported (from within a portable extension, for example).

[hantsy]

Absolutely yes.

[Emily-Jiang]

The injectable relies Jakarta Dependency Injection not CDI. Let's not mix two things together. Jakarta Dependency Injection is not part of CDI but depend on CDI.