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Improve @Value documentation

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Improve "@ConfigurationProperties vs. @Value" documentation with the
recommendation that kebab-case is used with the `@Value` annotation.

Closes gh-20507
This commit is contained in:
Phillip Webb 2020-04-23 16:37:23 -07:00
parent 291165f060
commit 416cfc2c86
1 changed files with 7 additions and 2 deletions
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9
spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc
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@ -1303,7 +1303,7 @@ The following table summarizes the features that are supported by `@Configuratio
| <<boot-features-external-config-relaxed-binding,Relaxed binding>>
| Yes
| No
| Limited (see note below)
| <<appendix-configuration-metadata.adoc#configuration-metadata,Meta-data support>>
| Yes
@ -1315,7 +1315,12 @@ The following table summarizes the features that are supported by `@Configuratio
|===
If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with `@ConfigurationProperties`.
You should also be aware that, since `@Value` does not support relaxed binding, it is not a good candidate if you need to provide the value by using environment variables.
Doing so will provide you with structured, type-safe object that you can inject into your own beans.
If you do want to use `@Value`, we recommend that you refer to property names using their canonical form (kebab-case using only lowercase letters).
This will allow Spring Boot to use the same logic as it does when relaxed binding `@ConfigurationProperties`.
For example, `@Value("{demo.item-price}")` will pick up `demo.item-price` and `demo.itemPrice` forms from the `application.properties` file, as well as `DEMO_ITEMPRICE` from the system environment.
If you used `@Value("{demo.itemPrice}")` instead, `demo.item-price` and `DEMO_ITEMPRICE` would not be considered.
Finally, while you can write a `SpEL` expression in `@Value`, such expressions are not processed from <<boot-features-external-config-application-property-files,application property files>>.