Doc: MessageSource is identified by bean name, this is very confusing [SPR-4321]

[spring-projects-issues]

Alef Arendsen opened SPR-4321 and commented

MessageSource is (AFAIK) one of the few beans that are NOT automatically picked up by type by the application context. In the past ViewResolver and HandlerMapping were picked up by id too, but not anymore.

Can we change MessageSource to by picked up by type too instead of by name? It's very confusing to people right now I just learned...

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Affects: 2.0.8, 2.5.1

[spring-projects-issues]

Juergen Hoeller commented

Point taken, Alef. However, there are actually quite a few such beans left: e.g. "loadTimeWeaver", "applicationEventMulticaster" or also "viewNameTranslator" in a DispatcherServlet...

The basic rule is that bean names are used wherever there must be only one such bean from a delegation point of view. In contrast to that, by-type detection is used wherever any number of beans of such a type are supported.

This allows the single-bean case to define e.g. a custom "messageSource" entry point bean which in turn delegates to backend beans of type MessageSource but according to custom rules.

MessageSource delegation follows an inheritance rule at present, which is why there needs to be exactly one per ApplicationContext. Short of redefining that rule, by-type detection of MessageSources would arguably lead to messy semantics...

Juergen

[spring-projects-issues]

Jon Osborn commented

I agree. Maybe the issue is really lack of clear documentation on which beans are loaded by name and which by type?

[spring-projects-issues]

Arjen Poutsma commented

This behavior is already documented, see http://static.springframework.org/spring/docs/2.5.x/reference/beans.html#context-functionality-messagesource