How do you configure a Spring Boot application using YAML?

Table of Contents

Introduction

Spring Boot offers flexible ways to configure application settings, with the most common options being properties files (application.properties) and YAML files (application.yml). YAML (YAML Ain't Markup Language) is a human-readable data serialization format that is often preferred over properties files due to its hierarchical structure and readability. In this guide, we’ll explore how to configure a Spring Boot application using YAML and compare it with traditional properties-based configuration.

Why Use YAML for Configuration in Spring Boot?

YAML provides several advantages over properties files:

• Readability: YAML files are more readable and concise, especially for complex configurations.
• Hierarchical Structure: YAML allows you to define nested properties, making it easier to represent complex objects.
• Environment-Specific Profiles: YAML supports multiple profiles and environment-specific configurations more naturally.

Using YAML can make your configuration files cleaner and more organized, especially when dealing with large applications or multi-environment setups.

Basic YAML Configuration in Spring Boot

Spring Boot automatically supports YAML configuration out of the box, so you don't need additional dependencies to use it. The configuration settings in a application.yml file are structured in a key-value format, similar to properties files, but with a more readable and hierarchical layout.

Here’s a simple example of how to configure a Spring Boot application using YAML:

Example of application.yml

Explanation:

• Server Configuration: The server.port property sets the HTTP port for the application to 8081. The server.servlet.context-path defines the base URL path for the application.
• DataSource Configuration: The spring.datasource section configures the database connection details, including the database URL, username, and password.
• Thymeleaf Configuration: The spring.thymeleaf.cache disables caching for Thymeleaf templates during development.
• Logging Configuration: The logging.level section sets the logging levels for the root logger and Spring framework classes.

Advanced YAML Configuration Examples

Configuring Profiles

Spring Boot supports different environments (profiles) such as dev, test, and prod. YAML makes it easy to specify configuration values for different profiles within a single file.

Example of Profile-Specific Configuration

Explanation:

• Active Profile: The spring.profiles.active key sets the active profile to dev by default.
• Profile-Specific Configuration: The file uses multiple YAML documents separated by ---. Each section corresponds to a specific profile (dev and prod), with different database connection settings for each environment.

Configuring Custom Properties

You can also define custom properties for your application in YAML format.

Example of Custom Properties

You can then access these custom properties in your Spring Boot application like this:

Configuring External Configuration

Spring Boot allows you to load external configuration files using YAML. You can specify the location of an external YAML file in your application.yml or via command-line arguments.

Example of Loading External YAML File

Explanation:

• The spring.config.import directive specifies the path to an external YAML file that should be loaded. The optional: prefix ensures that the application doesn’t fail if the file is missing.

Practical Examples

Example 1: Configure Multiple Datasources

In a Spring Boot application, you might need to configure multiple data sources (e.g., for different database types or environments). YAML makes it easier to manage these configurations.

In this example, two data sources (primary and secondary) are configured, and Spring Boot will use them based on the configuration class annotations.

Example 2: Configuring a Spring Boot Web Application

If you’re working with a web application, you might want to configure settings for the embedded web server, such as the port, context path, or logging levels.

In this case, the application will run on port 8080, and all logs related to Spring MVC will be output at the DEBUG level.

Conclusion

Configuring a Spring Boot application using YAML is a clean, readable, and flexible approach. The hierarchical structure of YAML makes it particularly useful for complex applications with nested properties or multi-profile setups. By using application.yml, you can easily manage application configuration, set profile-specific values, and define custom properties, making your Spring Boot application more organized and easier to maintain.