Activating Maven Profiles

There are a few ways to activate Maven profiles depending on your needs. The most direct is using the -P flag, like mvn clean package -Pprod. That explicitly activates the prod profile for that build. But in real projects, you don't want to rely on developers remembering flags. So you can set activeByDefault to true in the profile definition, which means that profile runs automatically unless you activate a different one. For example, our dev profile might be activeByDefault so when someone clones the repo and runs mvn package, it just works with local settings. Then there's automatic activation based on conditions. You can activate a profile when an environment variable is set, like BUILD_ENV equals production. This is huge for CI/CD because your Jenkins or GitLab pipeline just exports BUILD_ENV equals production, and Maven activates the right profile automatically. The build logs show exactly what happened without relying on someone passing the right flag. You can also activate based on JDK version, which is useful if you're supporting multiple Java versions with different compiler settings. Or based on file presence — like only run integration tests if integration-test.properties exists. One thing to watch out for: if you use -P to explicitly activate a profile, all activeByDefault profiles get deactivated. So if you have a dev profile with activeByDefault true and you run mvn package -Pprod, only the prod profile is active. The dev one shuts off. That surprises freshers who expect both to run. In production environments, we typically use environment variable activation rather than -P flags because it's clearer in audit logs and less prone to human error.