Spring Boot Configuration -

Spring Boot Configuration is the mechanism used to define, externalize, and manage settings that control how an application behaves across different environments without modifying source code. It relies on a “convention over configuration” approach, providing sensible defaults while allowing developers to easily override settings such as server ports, database credentials, third-party API keys, and business rules.

Different types of Spring Boot application Configurations are

1. Application Properties

The application.properties file is the traditional, key-value-based approach to configuration in Spring Boot, typically located in the src/main/resources folder.

Uses a flat key=value format (e.g., server.port=8080 or spring.datasource.url=jdbc:mysql://...).
Simple to read and write, making it well-suited for smaller applications or straightforward setups.

2. YAML Configuration

YAML (application.yml or application.yaml) serves as an alternative to .properties files, using indentation to represent hierarchical data structures.

Avoids repetitive prefix names by grouping related properties under parent keys.
Supports complex types natively, such as nested maps, lists, and boolean structures.

3. Custom Configuration

Custom configuration allows you to define your own application-specific properties and bind them cleanly to Java objects instead of hardcoding values.

@Value annotation: Injects single configuration values directly into Spring-managed beans (e.g., @Value("${app.jwt.secret}")).
@ConfigurationProperties: Binds a group of related properties into a strongly typed, validated Java POJO/record, providing auto-completion and compile-time safety.
@Configuration & @Bean: Used in Java code to instantiate and configure beans manually when auto-configuration needs customization.

4. Environment Profiles

Spring Profiles provide a way to segregate parts of the application configuration and make them available only in specific runtime environments (such as dev, test, staging, or prod).

Implemented using profile-specific files like application-dev.properties or application-prod.yml.
Activated via properties (spring.profiles.active=dev), command-line arguments (--spring.profiles.active=prod), or OS environment variables.
Prevents accidental deployment of testing configurations (e.g., embedded databases) into production environments.

Getting Started with Spring Boot