Provide support for javax.inject.Provider<> style injection for @Value and @Autowired [SPR-6079]

[spring-projects-issues]

Mike Youngstrom opened SPR-6079 and commented

Sometimes for @EL and @Autowired injection points the developer may not want the expression or the dependency evaluated at the time of injection but instead at a later point when the developer chooses to evaluate the injection. This is extremely useful for a number of reasons. Some of which are detailed in the javax.inject.Provider javadocs here.

http://atinject.googlecode.com/svn/trunk/javadoc/javax/inject/Provider.html

With the added desire that the injected Provider be Serializable.

It would be nice if specifically this portion of the javax.inject functionality could be included in Spring 3.0 since it is so valuable especially when coupled with @Value. I would be happy to provide an initial patch if there were a chance for this to make it into Spring 3.0.

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Affects: 3.0 M4

Issue Links:

• Provider<...> declaration for @Value method argument fails with TypeMismatchException [SPR-12297] #16903 Provider<...> declaration for @Value method argument fails with TypeMismatchException

Referenced from: commits 209f43b

[spring-projects-issues]

Juergen Hoeller commented

We actually have such an interface already: org.springframework.beans.factory.ObjectFactory. It's not promoted much but has been around for a while, usually to be set up via an ObjectFactoryCreatingFactoryBean (pretty old school, I know). We are also using the ObjectFactory interface in other scenarios, e.g. in the Scope SPI.

So I guess there is an obvious solution: Supporting injection of a generically typed ObjectFactory<T> using @Autowired / @Value. I'll prototype this for the Spring 3.0 timeframe still; if it's easy enough to do, it still has a chance to make it into 3.0. We'll fully support the actual JSR-330 Provider facility in Spring 3.1 then.

Juergen

[spring-projects-issues]

Mike Youngstrom commented

Ah, forgot about ObjectFactory. That would be perfect. If it would help getting it into 3.0 I could provide am initial PoC patch. Let me know.

Mike

[spring-projects-issues]

Juergen Hoeller commented

Should work fine in SVN trunk already :-)

We respect the generically declared ObjectFactory type <T>, if available. Otherwise we'll simply create a standard ObjectFactory<Object>, with the matching done against qualifiers or based on the @Value expression.

Juergen

[spring-projects-issues]

Mike Youngstrom commented

You rock!!! Looking at the source changes it appears to be just what I was looking for.

Thanks,
Mike