@Value cannot be used as aliased meta-annotation [SPR-13603]

[spring-projects-issues]

Jose Antonio Iñigo opened SPR-13603 and commented

It would be nice to be able to use @Value as meta annotation:

Having a properties file and the necessary context:properties-placeholder configuration...

someproperty=somevalue

In a Spring bean we could have:

@Value("${someproperty}")
private String someProperty;

Where someProperty's value would be "somevalue".

I want to create a new annotation @Refreshable with @Value as meta-annotation so that it behaves the same as using @Value directly. Since @Value requires a value I hardcode "default" hoping that @Refreshable's value() will override it:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Value("default")
public @interface Refreshable {
    String value();
}

Then when I use the new annotation in a bean, I was expecting it to work properly, injecting the declared value "somevalue", but it doesn't, I get "default".

@Refreshable("${someproperty}")
private String someProperty;

---

Reference URL: http://stackoverflow.com/questions/32964391/annotation-with-spring-value-meta-annotation-not-injecting-the-value

Issue Links:

• @AliasFor attribute name should default to declaring attribute [SPR-13828] #18401 @AliasFor attribute name should default to declaring attribute
• Support @AliasFor for @JmsListener attributes [SPR-13803] #18376 Support @AliasFor for @JmsListener attributes

Referenced from: commits 4f95593

[spring-projects-issues]

Juergen Hoeller commented

I'm afraid you're running into a limitation of our name-based attribute overriding here: You can't override value attributes, since those are not reliably meant to override a specific meta-annotation's value attribute.

That said, as of Spring Framework 4.2, you can declare an explicit AliasFor annotation that should point to Value.class in your case, indicating that you intend to override that annotation's value attribute. Any other meta-annotation's value attribute will remain untouched. Does this work in your scenario?

Juergen

[spring-projects-issues]

Jose Antonio Iñigo commented

Hi Juergen, first of all, thank you for your quick anwer. I tried @AliasFor but unfortunately it didn't work.

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@Value("")
public @interface Refreshable {
	@AliasFor(annotation=Value.class, attribute="value")
	String value();
}

The value of the fields that use @Refreshable is always "".

Now removing @Value("") and keeping only the @AliasFor I get null:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Refreshable {
	@AliasFor(annotation=Value.class, attribute="value")
	String value();
}

Maybe I didn't understand well how to use @AliasFor...

[spring-projects-issues]

Juergen Hoeller commented

Checking the lookup algorithm there, we do not evaluate @AliasFor for @Value processing at all. So I'm afraid this is simply not supported at the moment; I was mistaken that we took it that far already. Anyway, since this really should be working, I'll put this onto the 4.3 roadmap, making sure that QualifierAnnotationAutowireCandidateResolver participates in the sophisticated merging of attributes that 4.2's AnnotatedElementUtils can do now.

Juergen

[spring-projects-issues]

Juergen Hoeller commented

This revision is in master now, allowing for @AliasFor references to @Value. Feel free to give the upcoming 4.3.0.BUILD-SNAPSHOT a try...

Juergen

[spring-projects-issues]

Sam Brannen commented

Thanks, Juergen Hoeller!

@Value somehow didn't make it into any of the candidate lists in #16020. I guess I just overlooked it... not sure how... but I obviously did. ;)

[spring-projects-issues]

Jose Antonio Iñigo commented

@Juergen I just tested it and works perfectly. Thank you for the quick solution!