What is application.yml in Spring Boot: Purpose and Usage

application.yml in Spring Boot is a configuration file written in YAML format that stores settings for your application. It helps organize properties like database info, server ports, and custom settings in a clear, hierarchical way.

How It Works

Think of application.yml as a neat notebook where you write down all the important settings your Spring Boot app needs to run. Instead of scattering these settings in many places, you keep them in one file with a clear structure.

YAML format uses indentation to show relationships, like chapters and subchapters in a book. This makes it easy to see which settings belong together. Spring Boot reads this file when the app starts and applies the settings automatically.

This is similar to setting up a recipe before cooking: you list ingredients and steps clearly so the cooking (app running) goes smoothly.

Example

This example shows a simple application.yml with server port and database settings. Spring Boot will use these values when running the app.

yaml

server:
  port: 8081

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mydb
    username: user
    password: pass

custom:
  feature-enabled: true

Output

The app runs on port 8081 and connects to the MySQL database at jdbc:mysql://localhost:3306/mydb with the given username and password. The custom feature is enabled.

When to Use

Use application.yml whenever you want to keep your app settings organized and easy to change without touching code. It is perfect for:

• Setting server ports, database connections, and security options.
• Defining different settings for development, testing, and production by using profiles.
• Adding custom configuration values your app needs.

This helps teams manage configurations clearly and safely, avoiding hard-coded values inside the app.

Key Points

• application.yml uses YAML format for clear, hierarchical configuration.
• Spring Boot automatically loads this file at startup.
• It centralizes app settings like ports, databases, and custom options.
• Supports profiles for environment-specific configurations.
• Makes configuration easy to read and maintain.

Key Takeaways

application.yml is a YAML file for organizing Spring Boot app settings.

It helps keep configuration clear, hierarchical, and easy to manage.

Spring Boot reads this file automatically when the app starts.

Use it to set server, database, and custom properties safely outside code.

Profiles in application.yml allow different settings per environment.