Introduce support in Spring Boot DevTools to automatically and optionally load a application-devtools.yml (or .properties) file as a local override configuration source during development.

Motivation
When developing Spring Boot applications, it is common to need local-only configuration such as:

  • Local service endpoints or ports
  • Developer-specific API keys or credentials
  • Debug or logging tweaks
  • Feature toggles or secrets

Currently, developers must choose between: - Creating profile-specific overrides (e.g., application-dev.yml) but there is no standard convention for what this file is called, so every project does something different, making it a bespoke effort to configure locally runnable boot app. - Using spring.config.import in application.yml, which adds complexity and clutter to the main configuration, and may accidentally leak dev-only paths into production environments.

Proposed Behavior
If DevTools is present on the classpath, Spring Boot would automatically and optionally import a config file named:

application-devtools.yml

(or .properties), if it exists in the same location(s) as the other config files (e.g., src/main/resources, or external locations).

  • It would not require any spring.config.import entry.
  • It would be gracefully ignored if not present.
  • Developers can .gitignore it by default:
    gitignore application-devtools.yml
  • IDEs and CLI builds using DevTools (bootRun) would pick it up transparently.

Benefits - Safer and cleaner than custom spring.config.import hacks. - Avoids bloating application.yml with dev-only logic. - Encourages best practices: local config override without leaking to production. - Improves parity with how spring-boot-devtools already supports dev-only beans and runtime behavior.

Thanks for considering this enhancement! It would make DevTools even more useful and offer a convention that makes all spring boot developers lives easier.