Dynamically Loading YAML Files in Spring Boot with Java

In modern applications, configuration plays a crucial role in maintaining flexibility and modularity. Often, we need to load properties from multiple YAML files, organized across nested directories, to ensure scalability and modular configuration. In this blog, we’ll explore how to dynamically load all YAML files from a specific directory structure and merge their properties into a single configuration object.

Use Case

Imagine we have a configuration directory like this:

src/main/resources

├── application.yml

├── configs

│   ├── environment

│   │   ├── dev.yml

│   │   ├── qa.yml

│   ├── features

│   │   ├── feature1.yml

│   │   ├── feature2.yml

We want to load all YAML files under the configs directory (including subdirectories), merge them, and make the properties available for use in our Spring Boot application.

Implementation

1. Dynamic YAML Loader

We will create a utility class to dynamically load and merge all YAML files into a single Properties object.

package com.example.config;

import org.springframework.beans.factory.config.YamlPropertiesFactoryBean;

import org.springframework.core.io.Resource;

import org.springframework.core.io.support.PathMatchingResourcePatternResolver;

import java.io.IOException;

import java.util.Properties;

public class DynamicYamlLoader {

    public static Properties loadYamlFiles(String basePath) throws IOException {

        Properties combinedProperties = new Properties();

        PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();

        // Use '**' to include all nested directories and `.yml` files

        Resource[] resources = resolver.getResources(basePath + "/**/*.yml");

        for (Resource resource : resources) {

            if (resource.exists() && resource.isReadable()) {

                YamlPropertiesFactoryBean yamlFactory = new YamlPropertiesFactoryBean();

                yamlFactory.setResources(resource);

                Properties yamlProperties = yamlFactory.getObject();

                if (yamlProperties != null) {

                    combinedProperties.putAll(yamlProperties);

                }

            }

        }

        return combinedProperties;

    }

}

2. Spring Configuration Loader

To integrate this loader into Spring, we’ll create a configuration class that loads the properties and makes them available in the application context.

package com.example.config;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import java.io.IOException;

import java.util.Properties;

@Configuration

public class AppConfig {

    @Bean

    public Properties dynamicProperties() throws IOException {

        // Specify the base directory

        String basePath = "classpath:/configs";

        return DynamicYamlLoader.loadYamlFiles(basePath);

    }

}

3. Example YAML Files

Here are some sample YAML files to simulate a realistic use case:

configs/environment/dev.yml:

app:

  name: DemoApp

  environment: development

logging:

  level: DEBUG

configs/features/feature1.yml:

feature1:

  enabled: true

  maxRetries: 3

configs/features/feature2.yml:

feature2:

  enabled: false

  timeout: 5000

4. Accessing Properties

You can now access the combined properties in your application. For example:

package com.example.service;

import org.springframework.stereotype.Service;

import java.util.Properties;

@Service

public class PropertyService {

    private final Properties properties;

    public PropertyService(Properties properties) {

        this.properties = properties;

    }

    public void printProperties() {

        System.out.println("App Name: " + properties.getProperty("app.name"));

        System.out.println("Feature1 Enabled: " + properties.getProperty("feature1.enabled"));

        System.out.println("Feature2 Timeout: " + properties.getProperty("feature2.timeout"));

    }

}

When running the application, the output will be:

App Name: DemoApp

Feature1 Enabled: true

Feature2 Timeout: 5000

Explanation

1. Recursive File Loading:

   • The PathMatchingResourcePatternResolver ensures all YAML files under the specified path (including subdirectories) are discovered.

2. Merging Properties:

   • Using Properties.putAll() allows us to combine properties from all YAML files. If duplicate keys exist, the last-loaded file overwrites the earlier values.

3. Spring Integration:

   • By declaring a @Bean, we make the combined properties available for dependency injection.