Spring Profiles provide a flexible way to load environment-specific configurations in a Spring-based application. Here’s a step-by-step guide on how to use them:

Steps to Inject Environment-Specific Values Using Spring Profiles

1. Define Profile-Specific Properties Files
   Create separate property files for different environments (e.g., development, testing, production). Make sure to name them with a clear convention.

   Examples:

   • application-dev.properties (for development)
   • application-prod.properties (for production)
   • application-test.properties (for testing)

   In these files, define environment-specific values.
   Example (application-dev.properties):

   app.name=MyApp (Dev Environment)
   app.url=http://localhost:8080
   

   Example (application-prod.properties):

   app.name=MyApp (Production)
   app.url=https://myapp.com
   

2. Activate the Profile
   Use one of the following methods to specify which profile is active:
   • In application.properties or application.yml: Add the spring.profiles.active property.

   spring.profiles.active=dev
   

   • As a Command-Line Argument:
     You can pass the profile during application startup:

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

   • As an Environment Variable:
     Set the SPRING_PROFILES_ACTIVE environment variable:

   export SPRING_PROFILES_ACTIVE=prod
   

3. Use the @Profile Annotation in Beans (Optional)
   Annotate components or configurations that should only load in specific profiles using the @Profile annotation.

   Example:

   @Component
   @Profile("dev")
   public class DevDatabaseInitializer { 
       public DevDatabaseInitializer() {
          System.out.println("Initializing Development Database...");
       }
   }
   

   The above bean will only be loaded when the “dev” profile is active.

4. Access Values from Properties Files
   Use @Value or the @ConfigurationProperties annotation to inject values into your code.

   Example:

   @Component
   public class AppConfig {
       @Value("${app.name}")
       private String appName;
   
       @Value("${app.url}")
       private String appUrl;
   
       public void printConfig() {
          System.out.println("App Name: " + appName);
          System.out.println("App URL: " + appUrl);
       }
   }
   

5. (Optional) Use application.yml for Profile-Specific Configuration
   Instead of multiple property files, you can use a single application.yml with profile-specific sections:

   spring:
     profiles:
       active: dev
   
   ---
   spring:
     profiles: dev
     app:
       name: MyApp (Dev Environment)
       url: http://localhost:8080
   
   ---
   spring:
     profiles: prod
     app:
       name: MyApp (Production)
       url: https://myapp.com
   

Using Spring Profiles allows you to maintain clean and environment-specific configurations, reducing the chance of errors and simplifying the deployment process.