@Profile Annotation in Spring Explained

Direct Answer

@Profile makes a component or @Bean definition active only when a profile expression matches the Environment's active profiles. @Profile("dev") enables it for dev; @Profile("!prod") matches when prod is not active. Profiles select bean/configuration variants at context creation. Profile-specific config files change values and are related, but they are not the same mechanism.

Code Example

@Configuration
public class DataSourceConfig {

    @Bean
    @Profile("dev")  // Only created when dev profile is active
    public DataSource devDataSource() {
        var ds = new EmbeddedDatabaseBuilder()
                .setType(EmbeddedDatabaseType.H2)
                .addScript("classpath:schema.sql")
                .build();
        System.out.println("Using H2 in-memory database for dev");
        return ds;
    }

    @Bean
    @Profile("prod")  // Only created when prod profile is active
    public DataSource prodDataSource() {
        var ds = new HikariDataSource();
        ds.setJdbcUrl("jdbc:postgresql://prod-db.example.com:5432/appdb");
        ds.setUsername("produser");
        ds.setPassword(System.getenv("DB_PASSWORD"));  // From environment variable
        ds.setMaximumPoolSize(20);
        System.out.println("Using PostgreSQL production database");
        return ds;
    }

    @Bean
    @Profile("test")  // Only for integration tests
    public DataSource testDataSource() {
        return new EmbeddedDatabaseBuilder()
                .setType(EmbeddedDatabaseType.H2)
                .build();
    }
}

Common Mistakes & Pitfalls

• Confusing @Profile with profile-specific properties: Freshers think @Profile("dev") and application-dev.properties are the same. They're complementary. Profile-specific properties change configuration values. @Profile changes which beans exist. Use properties for values, @Profile for implementations.
• No default profile: If you mark all DataSource beans with @Profile and forget to activate a profile, Spring has no DataSource and the app crashes. Always provide a @Profile("default") bean or use @Profile("!prod") to mean "anything except prod".
• Hardcoding profile checks: Freshers write if (activeProfile.equals("dev")) instead of using @Profile. This scatters environment logic everywhere. Let Spring handle it declaratively.
• Not testing profile activation: In production, you set spring.profiles.active=prod via environment variable or command-line. Freshers forget to test this and deploy without activating the right profile, causing the app to use the wrong database.