Nested external configuration classes in Spring Boot

Question

I want to inject my application.yml into a nested Map like this:

application.yml

components:
  component1:
    host: host1
    port: 1111
  component2:
    host: host2
    port: 2222
  component3:
    host: host3
    port: 3333

MyComponents.java

@Component
@ConfigurationProperties
public class MyComponents {
  Map<String, MyComponent> components;

  public class MyComponent {
    String host;
    Integer port;
    
    //empty constructor, getters, setters
  }

  //empty constructor, getters, setters
}

But even if I don't instantiate the object ( @Autowire ), I'm getting the following error message:

org.springframework.beans.NullValueInNestedPathException: Invalid property 'components[component1]' of bean class [package.path.MyComponents]: Could not instantiate property type [package.path.MyComponents$MyComponent] to auto-grow nested property path: java.lang.InstantiationException: package.path.MyComponents$MyComponent

How do I get the configuration into my class layout?

Answer 1

The inner class MyComponent has to be static :

@Component
@ConfigurationProperties
public class MyComponents {
  Map<String, MyComponent> components;

  public static class MyComponent {
    String host;
    Integer port;
    
    //empty constructor, getters, setters
  }

  //empty constructor, getters, setters
}

---

_{This answer was posted as an edit to the question Nested external configuration classes in Spring Boot by the OP Squall under CC BY-SA 3.0.}