Document that constructor binding does not support @DurationUnit and @DataSizeUnit

[jordigarcl]

According to this documentation, I should be able to use @DurationUnit to change the default unit when converting a duration. However, the example above keeps using MILLISECONDS as the duration unit.

Happening in the latest Spring version

1. When not specifying a unit in application.yml:

myconfig:
  myDuration: 70

2. And specifying DurationUnit to SECONDS in config properties class

@ConstructorBinding
@ConfigurationProperties("myconfig")
class MyProperties(
  @DurationUnit(ChronoUnit.SECONDS)
  val myDuration: Duration,
)

3. Then duration is converted using default MILLISECONDS unit

myProperties.myDuration.toString() // -> "PT0.07S"

[jordigarcl]

Also, I don't understand why the current documentation provides this example:

@ConfigurationProperties("app.system")
public class AppSystemProperties {

    @DurationUnit(ChronoUnit.SECONDS)
    private Duration sessionTimeout = Duration.ofSeconds(30);
}

Why is it programmatically setting Duration.ofSeconds(30) ? Isn't the whole purpose to use the properties value?

[wilkinsona]

Duration.ofSeconds(30) is the default value for the app.system.sessionTimeout property.

[wilkinsona]

This has been addressed in 2.4 where @DurationUnit can now be used on constructor parameters. I think we still need to do something in a maintenance branch, though. The problem isn't specific to Kotlin as the following Java does not work either:

@DurationUnit(ChronoUnit.SECONDS) 
private final Duration duration;

public MyProperties(Duration duration) {
	this.duration = duration;
}

We can't be sure that the duration constructor parameter will be stored in the duration field so there's no way of reliably discovering the duration unit. I suspect the best that we can do is to update the documentation to make it clear that @DurationUnit is only supported with JavaBean-based property binding.