Docs should explicit state how @ConfigurationProperties map to command line args and os env vars

[cer]

Suppose I have an @ConfigurationProperties class such as

@ConfigurationProperties(prefix = "foo.bar")
class BazProperties {

  @BeanProperty
  @Required
  var simple : String = null

  @BeanProperty
  @Required
  var compoundName : Int = 30
}

The docs don't appear to explicitly define how this class's properties map to command line args and OS environment variables, e.g. FOO_BAR_COMPOUNDNAME and/or FOO_BAR_COMPOUND_NAME

[snicoll]

This section of the doc mentions it http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#boot-features-external-config-application-property-files

But it would be better if we had an explicit section about it.

[cer]

I don't think this change is sufficient. It's still vague.

I think the documentation would be greatly improved if you had a specific example. ie. for a given configuration class with prefix xY (and x.y), and various properties, foo and fooBar. here are the possible (a) OS environment variables (b) command line arguments and (c) system properties that map to the arguments. Ironically, you have more detailed documentation of the random.* properties.

[snicoll]

Chris, the whole point is that those things are relaxed and we try to be as lenient as we can. As far as I know there is no difference between (a), (b) and (c) except that some OSs prevent some formats.

How about showing what you're after concretely?

[philwebb]

I'm glad you pushed for this because I found an anomaly with the way that we were binding camel case properties (see #2304).

I don't thing we should document all possible variations but I've added a table that shows three of the common forms and when they might be used. Feel free to raise another issue if you think we should add some more.