In Spring Boot applications, application.properties or application.yml are configuration files used to externalize the application’s configuration settings. These files provide a convenient way to customize and manage settings such as database connections, server ports, logging configurations, and other environment-specific properties.

  • application.properties: A simple key-value pair format.

  • application.yml: A more readable YAML format, allowing hierarchical and nested configurations.

Purpose

  1. Separation of Concerns: Keeps configuration separate from code.

  2. Environment-Specific Settings: Easily configure different environments (dev, prod, test) by using profiles.

  3. Centralized Configuration: Manage properties like database URLs, server ports, etc., in one place.

Example (application.properties)

server.port=8080
spring.datasource.url=jdbc:mysql://localhost:3306/mydb

In short: These files store configurable properties for a Spring Boot application, making it easy to customize and manage settings.