How Does Spring Boot Manage Multiple External Configuration Files and Their Precedence?

Managing Multiple External Configuration Files in Spring Boot

Spring Boot facilitates the loading of properties from external configuration files. However, understanding the precedence and override mechanisms is crucial for effectively managing multiple files.

External Configuration File Precedence

Spring Boot reads property files in a specific order, with subsequent files overriding properties set in earlier ones. The default precedence is as follows:

1. Command line arguments
2. System properties
3. Environment variables
4. Application properties outside the jar (e.g., application.properties, application.yml)
5. Application properties inside the jar (e.g., application.properties, application.yml)

spring.config.location Property

To specify external property files, use the spring.config.location property. This property accepts a comma-separated list of file locations or directories.

Example:

-Dspring.config.location=my-config/,classpath:additional.properties

File Locations:

• my-config/ (directory containing application.properties or other valid file extensions)
• classpath:/additional.properties (file located on the classpath)

spring.config.additional-location Property

In Spring Boot 2.x, the spring.config.additional-location property is used to add external configuration files without overriding defaults. This is a change from 1.x, where spring.config.location replaced defaults.

Example:

-Dspring.config.additional-location=my-additional-config/

Overriding Default Properties

To override default properties with external files, ensure that the external files contain properties with the same names as the default properties. The external files should be included using spring.config.location or spring.config.additional-location.

Considerations for Workspace Configuration

In the context of workspace configuration (e.g., using an external config folder in the current working directory), specify the folder location using -Dspring.config.location=file:./config. This will ensure that your workspace configuration folder takes precedence over the default properties.

Custom Property Resolution

Custom property resolution mechanisms can also be implemented. For example, you can use @PropertySource annotations on @Configuration classes to specify custom property locations. However, remember that custom properties will override properties set in the default or external configuration files.

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