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Document that placeholders should us the canonical property name form

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Closes gh-31309
This commit is contained in:
Phillip Webb 2022-06-13 18:18:23 -07:00
parent 5ef5497680
commit b3a46fc50e
1 changed files with 15 additions and 2 deletions
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17
spring-boot-project/spring-boot-docs/src/docs/asciidoc/features/external-config.adoc
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@ -458,6 +458,15 @@ The use of placeholders with and without defaults is shown in the following exam
Assuming that the `username` property has not been set elsewhere, `app.description` will have the value `MyApp is a Spring Boot application written by Unknown`.
[NOTE]
====
You should always refer to property names in the placeholder using their canonical form (kebab-case using only lowercase letters).
This will allow Spring Boot to use the same logic as it does when <<features#features.external-config.typesafe-configuration-properties.relaxed-binding, relaxed binding>> `@ConfigurationProperties`.
For example, `${demo.item-price}` will pick up `demo.item-price` and `demo.itemPrice` forms from the `application.properties` file, as well as `DEMO_ITEMPRICE` from the system environment.
If you used `${demo.itemPrice}` instead, `demo.item-price` and `DEMO_ITEMPRICE` would not be considered.
====
TIP: You can also use this technique to create "`short`" variants of existing Spring Boot properties.
See the _<<howto#howto.properties-and-configuration.short-command-line-arguments>>_ how-to for details.
@ -1222,10 +1231,14 @@ The following table summarizes the features that are supported by `@Configuratio
|===
[[features.external-config.typesafe-configuration-properties.vs-value-annotation.note]]
NOTE: 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`.
[NOTE]
====
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 <<features#features.external-config.typesafe-configuration-properties.relaxed-binding, 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.
====
If you define a set of configuration keys for your own components, we recommend you group them in a POJO annotated with `@ConfigurationProperties`.
Doing so will provide you with structured, type-safe object that you can inject into your own beans.