How to Load Multiple External Configuration Files and Override Defaults in Spring Boot?

Loading Multiple External Configuration Files in Spring Boot

Context:

In Spring Boot, loading properties from external files is essential for configuring an application and managing environmental-specific settings. This article addresses the challenge of loading multiple external configuration files while overriding default ones stored in the classpath.

Understanding Property Resolution:

Spring Boot follows a specific order for loading and resolving properties:

• Command-line arguments
• System properties
• Environment variables
• Application properties outside the JAR
• Application properties inside the JAR
• Properties via @PropertySource annotations
• Default properties

Adding External Configuration Files:

To add external configuration files to your project, use the spring.config.location property, which accepts a comma-separated list of paths or directories.

Spring Boot 1.x:

In Spring Boot 1.x, the spring.config.location property simply extended the existing list of default files. This meant that the external files would not override any defaults unless explicitly specified.

Spring Boot 2.x and Higher:

In Spring Boot 2.x and later, the behavior of spring.config.location has changed. It now overrides the default properties instead of appending to them. To preserve the default configurations while adding external ones, use the spring.config.additional-location property.

Example:

To load two external configuration files and override the job-specific properties from the default set:

In this case, the job1.properties and job2.properties files will override any job-related properties defined in defaults.properties. The remaining properties in defaults.properties will be preserved.

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