Construct @ConfigurationProperties programmatically

I need to load a pretty complex object from application properties. The problem is, that I have to operate inside an ApplicationListener<ApplicationPreparedEvent>, aka the application is not fully loaded yet. So I guess, any annotation based approach is off reach.

Is there a way to get the same functionality in a programmatic way? I have access to the ConfigurableEnvironment and all the properties are already loaded.

What I tried so far:

• Iterate all ConfigurableEnvironment::getPropertySources
• Filter the ones that are instance of EnumerablePropertySource
• collect all their properties and write them into a String
• Use Jackson's JavaPropsMapper to convert this string to my model

Super hacky. It kinda works, except one detail: arrays coming from different PropertySources get "merged" instead of the expected behaviour, where the array with the higher precedence completely overrides the lower precedence ones. I need this to work as expected since I have profile-specific application-xxx.yaml files that are expected to override the default arrays from application.yaml. The expected array-overriding behaviour is described here: Combine list from multiple spring-boot YAML files

So, seems like my hacky solution implements some @ConfiruationProperties features, but not others. Feels like I am reinventing the wheel, and doing so badly.

Is there a solution where I get the proper functionality of @ConfigurationProperties in my ApplicationListener?

Spring Boot exposes org.springframework.boot.context.properties.bind.Binder, which you can use like this:

import org.springframework.boot.context.event.ApplicationPreparedEvent;
import org.springframework.boot.context.properties.bind.Binder;
import org.springframework.boot.context.properties.source.ConfigurationPropertySources;
import org.springframework.context.ApplicationListener;
import org.springframework.core.env.ConfigurableEnvironment;

public class MyApplicationPreparedListener implements ApplicationListener<ApplicationPreparedEvent> {

    @Override
    public void onApplicationEvent(ApplicationPreparedEvent event) {
        ConfigurableEnvironment env = event.getApplicationContext().getEnvironment();
        Binder binder = new Binder(ConfigurationPropertySources.get(env));

        MyComplexConfig config = binder.bind("my.config", MyComplexConfig.class)
                .orElseThrow(() -> new IllegalStateException("Could not bind config"));

        System.out.println("Loaded config:");
        System.out.println("  name: " + config.getName());
        System.out.println("  servers: " + config.getServers());
        System.out.println("  timeout: " + config.getNested().getTimeout());
        System.out.println("  labels: " + config.getNested().getLabels());
    }
}

Lets take a configuration properties file and two YAMLs like this:

import lombok.Getter;
import lombok.Setter;

import java.util.List;
import java.util.Map;

@Getter
@Setter
public class MyComplexConfig {
    private String name;
    private List<String> servers;
    private NestedConfig nested;

    @Getter
    @Setter
    public static class NestedConfig {
        private int timeout;
        private Map<String, String> labels;
    }
}

application.yaml

my:
  config:
    name: DefaultConfig
    servers:
      - default1.server.com
      - default2.server.com
    nested:
      timeout: 30
      labels:
        env: prod
        region: us-east

application-dev.yaml

my:
  config:
    name: DevConfig
    servers:
      - dev1.server.local
    nested:
      timeout: 10
      labels:
        env: dev
        debug: true

SpringBootApplication class:

import com.example.MyApplicationPreparedListener;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;

@SpringBootApplication
public class ExampleApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(ExampleApplication.class)
                .profiles("dev") // remove it to run with default profile
                .listeners(new MyApplicationPreparedListener()) 
                .run(args);
    }
}

Output for default profile:

Loaded config:
  name: DefaultConfig
  servers: [default1.server.com, default2.server.com]
  timeout: 30
  labels: {env=prod, region=us-east}

Output for dev profile:

Loaded config:
  name: DevConfig
  servers: [dev1.server.local]
  timeout: 10
  labels: {env=dev, debug=true, region=us-east}