Spring Boot

Article 6: Configuration & Properties in Spring Boot

By Utility Zone · 2026-01-27T18:30:29.786091

1. Introduction

Real applications never have hardcoded values.

Things like:

  • Server port
  • Database URL
  • API keys
  • Feature flags

must change without changing code.

Spring Boot provides a powerful and clean way to handle configuration.

2. The application.properties File

This is the default configuration file located at:

src/main/resources/application.properties

Example:

server.port=8081
spring.application.name=demo-app

Spring Boot automatically reads this file at startup.

3. Using @Value to Read Properties

3.1 Define a Property

app.message=Hello from properties file

3.2 Inject the Property

@RestController
public class ConfigController {

    @Value("${app.message}")
    private String message;

    @GetMapping("/config-message")
    public String getMessage() {
        return message;
    }
}

Open:

http://localhost:8081/config-message

4. Common application.properties Examples

server.port=8081
logging.level.root=INFO
spring.application.name=my-spring-app

Avoid putting secrets directly here for production.

5. Using application.yml (YAML)

Spring Boot supports YAML as an alternative.

Example:

server:
  port: 8081

spring:
  application:
    name: my-spring-app

✔ Cleaner for large configs
❌ Indentation-sensitive

Choose either .properties or .yml, not both.

6. Configuration Using @ConfigurationProperties

Best for grouped configuration.

6.1 Define Properties

app.name=Demo App
app.version=1.0

6.2 Create Config Class

@Component
@ConfigurationProperties(prefix = "app")
public class AppConfig {

    private String name;
    private String version;

    // getters and setters
}

Spring automatically maps values.

7. Environment-Specific Configuration (Profiles)

Applications behave differently in:

  • dev
  • test
  • prod

Spring Boot supports profiles.

7.1 Create Profile Files

application-dev.properties
application-prod.properties

Example:

server.port=8082

7.2 Activate Profile

spring.profiles.active=dev

Or via command line:

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

8. External Configuration (Important)

Spring Boot allows config from:

  1. application files
  2. Environment variables
  3. Command-line arguments

Priority:

Command line > Env vars > application.properties

9. Common Configuration Mistakes

❌ Typo in property key
❌ Missing ${} in @Value
❌ Mixing .yml and .properties
❌ Forgetting active profile

10. What You Should Understand Before Moving On

You should now know:

  • How Spring Boot reads configuration
  • Difference between .properties and .yml
  • When to use @Value vs @ConfigurationProperties
  • How profiles work

11. What’s Next?

➡ Article 7: Spring Boot + JPA + Hibernate

  • Databases
  • Entities
  • ORM basics

Type Next when you’re ready.