Profiles — @Profile, spring.profiles.active. How to activate.

Profiles let you register different beans and load different properties per environment — dev, test, prod — without changing code. Two mechanisms do the work: @Profile gates beans, and spring.profiles.active selects which profiles are live.

Gating beans with @Profile

@Profile on a @Component, @Configuration, or @Bean method makes it eligible only when the named profile is active:

@Configuration
public class MailConfig {

    @Bean
    @Profile("prod")
    MailSender smtpSender() { return new SmtpMailSender(...); }

    @Bean
    @Profile("!prod")          // any profile except prod
    MailSender loggingSender() { return new LoggingMailSender(); }
}

The expression supports !, &, | and grouping: @Profile("prod & eu"). A bean with no @Profile is always registered.

Profile-specific properties

Files named application-<profile>.yml/.properties are loaded only when that profile is active, layered on top of the plain application.yml:

application.yml          # common defaults
application-dev.yml      # loaded when 'dev' is active
application-prod.yml     # loaded when 'prod' is active

How to activate a profile

Many ways, highest precedence last (same hierarchy as any property):

# 1. In application.properties (the default fallback)
spring.profiles.active=dev

# 2. Command line — wins over the file
java -jar app.jar --spring.profiles.active=prod

# 3. JVM system property
java -Dspring.profiles.active=prod -jar app.jar

# 4. Environment variable (relaxed binding) — common in Docker/K8s
export SPRING_PROFILES_ACTIVE=prod

// 5. Programmatically, before refresh
new SpringApplicationBuilder(App.class)
    .profiles("prod")
    .run(args);

You can activate several at once: --spring.profiles.active=prod,eu,metrics.

Useful extras

• spring.profiles.include / profile groups (spring.profiles.group.prod=eu,metrics) activate bundles of profiles together.
• @ActiveProfiles("test") sets profiles in integration tests.
• If no profile is set, the default profile applies — beans annotated @Profile("default") run only when nothing else is active.