Nested Spring configuration (ConfigurationProperties) in records

Question

How can one map an application.yaml configuration with nested properties to a similar record structure in Java?

Eg, if we have the following yaml:

foo:
    bar:
        something: 42

    baz:
        otherThing: true

    color: blue

The desired record structure would be something along the lines of:

@ConfigurationProperties(prefix = "foo")
@ConstructorBinding
public record Foo(
    Bar bar,
    Baz baz,
    String color
) {}

// ---

@ConfigurationProperties(prefix = "foo.bar")
@ConstructorBinding
public record Bar(
    int something
) {}

// ---

@ConfigurationProperties(prefix = "foo.baz")
@ConstructorBinding
public record Baz(
    boolean otherThing
) {}

Answer 1

You don't need @ConfigurationProperties for each nested class. It only for the root class (Foo.class). Then make the Foo as Spring Bean by inserting @Component above the class or put @ConfigurationPropertiesScan on the Application class.

Answer 2

Turns out I didn't ask the correct question for the issue I had:/ So for the case people find this topic from a similar issue, the answer to my actual issue follows here.

The problem arises with a nested yaml trying to "short cut" on the model hierarchy, so given the following yaml:

foo:
    bar:
        baz:
            bum: "hello"

I was trying to model the hierarchy as follows:

@ConfigurationProperties(prefix = "foo")
@ConstructorBinding
public record Foo(BarBaz barBaz) {}

// --- 

@ConfigurationProperties(prefix = "foo.bar.baz")
@ConstructorBinding
public record BarBaz(String bum) {}

Here the problem arises that Foo cannot do constructor binding for BarBaz (not sure why). So there are two possible solutions that I found:

1. Do the full modelling (decided that this is what I prefer)

That is, don't try to skip the middle model for bar .

@ConfigurationProperties(prefix = "foo")
@ConstructorBinding
public record Foo(Bar bar) {}

// ---

@ConfigurationProperties(prefix = "foo.bar")
@ConstructorBinding
public record Bar(Baz baz) {}

// --- 

@ConfigurationProperties(prefix = "foo.bar.baz")
@ConstructorBinding
public record Baz(String bum) {}

2. Don't use @ConstructorBinding when embedding more nestings

Simply skip the constructor binding in Foo .

@ConfigurationProperties(prefix = "foo")
public record Foo(BarBaz barBaz) {}

// --- 

@ConfigurationProperties(prefix = "foo.bar.baz")
@ConstructorBinding
public record BarBaz(String bum) {}

Although simpler, it's less consistent.

Answer 3

I think for simplification you can just create a single file with:

@ConfigurationProperties(prefix = "foo")
public record Foo(Bar bar) {
    public record Bar(Baz baz) {
        public record Baz(String bum) {}    
    }
}

and this is working fine in spring-boot and you don't need to repeat annotations and when using it you will just use:

String bumVal = foo.bar().baz().bum();

where foo is just injected in your Bean(s) where you need it.

I removed even the @ConsructorBinding as since spring-boot 2.6 it is no more needed as long the record defines only one constructor, see release notes .

The above configuration relates to your own answer structure, but here is also the compact way for the original questions structure:

@ConfigurationProperties(prefix = "foo")
public record Foo(Bar bar, Baz baz, String color) {
    public record Bar(String something) {
    }
    public record Baz(String otherThing) {
    }   
}

I found the record type very useful for this use case as very compact and not too much code to write.