Spring Boot: read list of objects from yaml using @ConfigurationProperties is always returning null

The root cause is that the new SpringBoot will not parse the properties file as yaml properties.

You need add a Yaml PropertiesSourceFactory class first. Like below:

import java.io.IOException;
import java.util.Properties;

import org.springframework.beans.factory.config.YamlPropertiesFactoryBean;
import org.springframework.core.env.PropertiesPropertySource;
import org.springframework.core.env.PropertySource;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.core.io.support.PropertySourceFactory;

public class YamlPropertySourceFactory implements PropertySourceFactory {

    @Override
    public PropertySource<?> createPropertySource(String name, EncodedResource encodedResource) throws IOException {
        YamlPropertiesFactoryBean factory = new YamlPropertiesFactoryBean();
        factory.setResources(encodedResource.getResource());

        Properties properties = factory.getObject();

        return new PropertiesPropertySource(encodedResource.getResource().getFilename(), properties);
    }
}

Then in the class of: ConstantsProperties, you need specify the Factory class explicitly. like:

import java.util.List;

import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.PropertySource;
import org.springframework.stereotype.Component;

import lombok.Data;

@Data
@Component
@PropertySource(value = "classpath:constantsConfiguration.yml", factory = YamlPropertySourceFactory.class)
@ConfigurationProperties(prefix = "constants")
public class ConstantProperties {
    private List<User> myList;

    @Data
    public static class User {
        private String id;
        private String name;
        private String firstName;
        private Boolean allowed;

    }

}

Finally, Please pay attention to your yaml file format. Each separator should be 2 ' ' blank chars.

Please try it , it should work now.

@SeanH 's answer didn't work to me. The way I found to make it parse lists of objects from a yaml is using a list of a map. Then you will need to convert each map into the object you want:

First create YamlPropertySourceFactory as SeanH explained, and then in the ConstantProperties.class:

@Component
@PropertySource(value = "classpath:constantsConfiguration.yml", factory = YamlPropertySourceFactory.class)
@ConfigurationProperties(prefix = "constants")
public class ConstantProperties {
    private List<Map<String, String>> myList;

    public List<User> getUserList() {
        List<User> users = new ArrayList<>();
        myList.forEach(userInfo -> {
            User user = new User(userInfo.get("id"),
                                 userInfo.get("name"),
                                 userInfo.get("firstName"),
                                 Boolean.valueOf(userInfo.get("allowed")));
            users.add(user);
        });
        return users;
    }

    public static class User {
        private String id;
        private String name;
        private String firstName;
        private Boolean allowed;

        public User(String id, String name, String firstName, Boolean allowed) {
            this.id=id;
            this.name=name;
            this.firstName=firstName;
            this.allowed=allowed;
        }

        // Add Getters and Setters
    }
}