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Explicit note on self references 

Issue: SPR-14402
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Juergen Hoeller 2016-07-02 14:58:54 +02:00
parent b204437cef
commit c6752e6023
1 changed files with 16 additions and 1 deletions
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@ -4634,13 +4634,28 @@ If you intend to express annotation-driven injection by name, do not primarily u
`@Autowired`, even if is technically capable of referring to a bean name through `@Autowired`, even if is technically capable of referring to a bean name through
`@Qualifier` values. Instead, use the JSR-250 `@Resource` annotation, which is `@Qualifier` values. Instead, use the JSR-250 `@Resource` annotation, which is
semantically defined to identify a specific target component by its unique name, with semantically defined to identify a specific target component by its unique name, with
the declared type being irrelevant for the matching process. the declared type being irrelevant for the matching process. `@Autowired` has rather
different semantics: After selecting candidate beans by type, the specified String
qualifier value will be considered within those type-selected candidates only, e.g.
matching an "account" qualifier against beans marked with the same qualifier label.
For beans that are themselves defined as a collection/map or array type, `@Resource` For beans that are themselves defined as a collection/map or array type, `@Resource`
is a fine solution, referring to the specific collection or array bean by unique name. is a fine solution, referring to the specific collection or array bean by unique name.
That said, as of 4.3, collection/map and array types can be matched through Spring's That said, as of 4.3, collection/map and array types can be matched through Spring's
`@Autowired` type matching algorithm as well, as long as the element type information `@Autowired` type matching algorithm as well, as long as the element type information
is preserved in `@Bean` return type signatures or collection inheritance hierarchies. is preserved in `@Bean` return type signatures or collection inheritance hierarchies.
In this case, qualifier values can be used to select among same-typed collections,
as outlined in the previous paragraph.
As of 4.3, `@Autowired` also considers self references for injection, i.e. references
back to the bean that is currently injected. Note that self injection is a fallback;
regular dependencies on other components always have precedence. In that sense, self
references do not participate in regular candidate selection and are therefore in
particular never primary; on the contrary, they always end up as lowest precedence.
In practice, use self references as a last resort only, e.g. for calling other methods
on the same instance through the bean's transactional proxy: Consider factoring out
the affected methods to a separate delegate bean in such a scenario. Alternatively,
use `@Resource` which may obtain a proxy back to the current bean by its unique name.
`@Autowired` applies to fields, constructors, and multi-argument methods, allowing for `@Autowired` applies to fields, constructors, and multi-argument methods, allowing for
narrowing through qualifier annotations at the parameter level. By contrast, `@Resource` narrowing through qualifier annotations at the parameter level. By contrast, `@Resource`