Spring Profiles

Spring Profiles separate configuration settings and manage bean lifecycles per environment. They work by loading profile-specific application-{profile} files and conditionally instantiating beans annotated with @Profile("{profile}"). Profiles can be activated via the spring.profiles.active property, environment variables, or command-line parameters."

1. Core Concept: What Do Profiles Control?

Spring Boot Profiles primarily impact two main components:

• Configuration Files (Properties/YAML): Determines which configuration files are loaded into the environment.
• Spring Beans: Controls which Beans are created by the IoC container based on @Profile annotations.

2. Organizing Configuration Files by Profile

Option 1: Separate Files (Most Common).

Standard file naming pattern: application-{profile}.properties or application-{profile}.yml

• application.properties (Contains shared configurations common to all environments)
• application-dev.properties (DEV-specific configuration: Local/H2 DB, DEBUG log level)
• application-prod.properties (PROD-specific configuration: PostgreSQL Cluster DB, ERROR log level)

Option 2: Single Multi-Document YAML File (Using ---)

spring:
  application:
    name: my-app

---
spring:
  config:
    activate:
      on-profile: dev
server:
  port: 8080

---
spring:
  config:
    activate:
      on-profile: prod
server:
  port: 80

3. Applying Profiles to Beans with @Profile

You can attach @Profile to any @Component, @Service, @Repository, or @Configuration class/method. The bean will only be instantiated by the IoC Container if the matching profile is currently active.

public interface EmailService {
    void sendEmail(String to, String body);
}

// Only created in DEV or TEST profiles
@Service
@Profile({"dev", "test"})
public class MockEmailService implements EmailService {
    @Override
    public void sendEmail(String to, String body) {
        System.out.println("[MOCK EMAIL] Simulating email to: " + to);
    }
}

// Only created in PROD profile
@Service
@Profile("prod")
public class SmtpEmailService implements EmailService {
    @Override
    public void sendEmail(String to, String body) {
        // Real production logic connecting to AWS SES or SendGrid
    }
}

Profile Conditional Operators:.

• @Profile("dev"): Active when the dev profile is active.
• @Profile("!prod"): Active when the prod profile is NOT active.
• @Profile({"dev", "staging"}): Active if either dev OR staging is active.
• @Profile("dev & mysql"): Active only when both dev AND mysql profiles are active simultaneously.

4. How to Activate a Profile

here are several ways to tell Spring Boot which profile to activate. Below are the most common methods ordered by typical usage:

Method 1: Inside application.properties

spring.profiles.active=dev

Method 2: Command Line Argument (When running JAR).

This is the standard approach when deploying applications to servers or Docker/Kubernetes environments:

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

Method 3: Environment Variables

Ideal for CI/CD pipelines and containerized environments:

export SPRING_PROFILES_ACTIVE=prod
java -jar myapp.jar

Method 4: JVM System Property

java -Dspring.profiles.active=staging -jar myapp.jar

5. Property Override Order (Precedence)

When running the application with a specific profile (e.g., prod):

• Spring Boot loads the base application.properties file first.
• Then it loads the profile-specific application-prod.properties file.
• If a configuration key exists in both files, the profile-specific configuration (application-prod) overrides the base configuration.