[jsr330-eg] Issue 20 in atinject: make Injection optional

[atin...@googlecode.com]

Status: New
Owner: ----
Labels: Type-Defect Priority-Medium

New issue 20 by zhouyanming: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

like @Autowired(required=false) in spring

@Inject(required=false)
private UserService userService;

or

@Inject
@Optional
private UserService userService;

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[atin...@googlecode.com]

Comment #1 on issue 20 by mccallum.michael: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

That example is a bit contrived. How about injection of listeners to a
repository

public class UsefulRespository {

@Inject
Collection<UsefulUpdateListener> listeners

public void update(Useful u) {
store.replace(u);
for (UsefulUpdateListener l: listeners) {
l.notify(u);
}
}
}

The key aspect is that the repository does not care if there are listeners
but
provides the facility to notify them. Ideally if there were listeners they
would be
injected and if not an empty collection. I've been doing this for a long
time in
Spring using required=false and testing for nullity.

Obviously @Optional or @Required could be used to force it
not-null/not-empty but
have an indication that implementors do something consistent with
collections would
be really useful.

[atin...@googlecode.com]

Comment #2 on issue 20 by gavin.king: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

Surely an empty collection represents "no listeners". So I don't understand
your
usecase. You would only need some special "optional injection" feature if
you wanted
to inject null, not if you want to inject an empty collection.

[atin...@googlecode.com]

Comment #3 on issue 20 by limpbizkit: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

You could use something like Guice's multibindings to populate an
initially-empty set
with values. http://code.google.com/p/google-guice/wiki/Multibindings

[atin...@googlecode.com]

Comment #4 on issue 20 by zhouyanming: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

such feature implemented by both guice and spring,so why not add support in
jsr-330?

[atin...@googlecode.com]

Updates:
Status: Duplicate

Comment #5 on issue 20 by crazyboblee: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

We decided against supporting optional injection in JSR-330:
http://code.google.com/p/atinject/issues/detail?id=1&can=1&q=optional

[atin...@googlecode.com]

Comment #6 on issue 20 by zhouyanming: make Injection optional
http://code.google.com/p/atinject/issues/detail?id=20

how about provide a @Optional qualifier?