SpringBoot application properties

 What happens when you have default yaml or properties file along with the profile specific yml or properties files. eg: you have application.yml and application-dev.yml, application-test.yml, application-prod.yml

1. Default Behavior (No Active Profile)

• Only application.yml is loaded

• All other profile-specific files (-dev.yml, -test.yml, -prod.yml) are ignored

• Useful for shared configurations (e.g., app name, default server port)

---

2. When a Profile is Activated

If you activate a profile (e.g., dev):

1. application.yml is loaded first (base config)

2. application-dev.yml is merged on top, overriding matching properties

3. Other profile files (-test.yml, -prod.yml) are ignored

Example:

yaml

Copy

Download

# application.yml (shared)
server:
  port: 8080
logging:
  level:
    root: INFO

# application-dev.yml (dev-only)
logging:
  level:
    root: DEBUG
    org.hibernate.SQL: TRACE

Result (--spring.profiles.active=dev):

yaml

Copy

Download

server:
  port: 8080  # From base
logging:
  level:
    root: DEBUG       # Overridden by dev
    org.hibernate.SQL: TRACE  # Added by dev

---

3. Key Rules

Rule	Explanation
Profile-specific files override base	application-dev.yml wins over application.yml
Last profile wins	If multiple profiles are active (dev,test), the rightmost profile's config takes precedence
Non-conflicting properties merge	Unique properties from all files are combined
spring.profiles.include	Force-include additional profiles (e.g., spring.profiles.include: db,security)

---

4. How to Activate Profiles

Option 1: Command Line

sh

Copy

Download

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

Option 2: Environment Variable

sh

Copy

Download

export SPRING_PROFILES_ACTIVE=test  # Linux/macOS
set SPRING_PROFILES_ACTIVE=test     # Windows

Option 3: In application.yml

yaml

Copy

Download

spring:
  profiles:
    active: dev  # Default profile (not recommended for production)

---

5. Advanced: Multi-Profile Activation

You can activate multiple profiles (e.g., dev + db-mysql):

sh

Copy

Download

--spring.profiles.active=dev,db-mysql

Spring Boot merges them in order (rightmost profile wins conflicts).

---

6. Best Practices

1. application.yml → Store default/shared configs

2. application-{profile}.yml → Store environment-specific overrides

3. Never commit secrets → Use application-{profile}.yml with Vault/Env vars for prod credentials

4. Use spring.config.activate.on-profile (YAML only) to conditionally include sections:

   yaml

   Copy

   Download

   # In application.yml
   spring:
     config:
       activate:
         on-profile: "dev"
   logging:
     level:
       root: DEBUG

---

7. Debugging Configuration

Check which profiles are active and property sources:

sh

Copy

Download

# Enable debug mode
java -jar app.jar --debug

Look for:

Copy

Download

The following profiles are active: dev
Property Sources:
  - application.yml
  - application-dev.yml

---

Summary

• Base + Profile-Specific: Configs merge, with profile files overriding defaults

• Profile Activation: Controls which -{profile}.yml files are loaded

• Order Matters: Last profile in a comma-separated list has highest priority

This system allows clean separation of environments while avoiding duplication.