Spring Boot Properties: application.properties vs application.yml

Spring Boot lets you configure your app without touching code by using configuration files. These files live in the src/main/resources folder and help control:

• Server port
• Database settings
• Logging levels
• Custom application properties

The two most commonly used Spring Boot Properties formats are:

• application.properties
• application.yml

Let’s explore how they differ and how to use them effectively.

📄 What is application.properties?

A simple key-value file format used for defining configuration.

🔧 Example:

server.port=8081
spring.datasource.url=jdbc:mysql://localhost:3306/testdb
spring.datasource.username=root
spring.datasource.password=secret
logging.level.org.springframework=DEBUG

✅ Pros:

• Simple to read/write for small apps
• Easy to grep or parse
• Familiar for traditional Java devs

📝 What is application.yml?

YAML (YAML Ain’t Markup Language) is a structured, hierarchical configuration format.

🔧 Same Example in YAML:

server:
  port: 8081

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/testdb
    username: root
    password: secret

logging:
  level:
    org:
      springframework: DEBUG

✅ Pros:

• Better for complex/nested properties
• More readable for large configs
• Preferred in Kubernetes and cloud-native apps

🔀 Key Differences

🎯 When to Use Which?

• Use application.properties if:
• Use application.yml if:

✅ Both formats are fully supported by Spring Boot — it’s a matter of preference.

👥 Multi-Profile Support

You can create profile-specific files like:

• application-dev.properties
• application-prod.yml

Activate a profile via:

spring.profiles.active=dev

Or use --spring.profiles.active=prod when starting your app.

🔍 Accessing Custom Properties

Example:

app:
  welcome: Hello from YAML!

You can bind this to a class:

@Component
@ConfigurationProperties(prefix = "app")
public class AppProperties {
    private String welcome;

    // Getter and Setter
}

Make sure you add:

@EnableConfigurationProperties(AppProperties.class)

🚫 Common Mistakes to Avoid

✅ Summary

Whether you choose .properties or .yml, Spring Boot Properties gives you the power to tweak your app without touching the code.

📘 External References

• 📖 Spring Boot External Configuration Docs