Spring Boot’s main config file.

• Used to externalize configuration, so don’t hardcode settings in Java classes.
• Can configure:
  • Database connections
  • JPA/Hibernate
  • Server port
  • Logging
  • Custom application properties

Supports multiple env

• Each profile can have its own configuration.
• Typical usage: application-{profile}.yml

How Spring Boot chooses profile:

1. Command line

java -jar myapp.jar --spring.profiles.active=prod

1. Env var

SPRING_PROFILES_ACTIVE=prod

1. In application.yml (less common)

spring:
	profiles:
		active:local

Overriding rules:

• application.yml → base config