Spring Boot Architecture

Spring Boot Architecture Standards

Application Entry Point

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

// @SpringBootApplication combines:
// @Configuration - source of bean definitions
// @EnableAutoConfiguration - auto-configure based on classpath
// @ComponentScan - scan for components in this package and below

Configuration Classes

@Configuration
public class AppConfig {

    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder) {
        return builder
            .setConnectTimeout(Duration.ofSeconds(5))
            .setReadTimeout(Duration.ofSeconds(30))
            .build();
    }

    @Bean
    @ConditionalOnProperty(name = "app.feature.enabled", havingValue = "true")
    public FeatureService featureService() {
        return new FeatureServiceImpl();
    }
}

// Conditional beans
@ConditionalOnProperty(...)      // Based on property
@ConditionalOnClass(...)         // Based on class presence
@ConditionalOnMissingBean(...)   // If no other bean exists
@ConditionalOnBean(...)          // If another bean exists
@ConditionalOnExpression(...)    // SpEL expression

Configuration Properties

@ConfigurationProperties(prefix = "app")
@Validated
public record AppProperties(
    @NotBlank String name,
    @NotNull Duration timeout,
    @Valid DatabaseProperties database
) {
    public record DatabaseProperties(
        String host,
        int port,
        @NotBlank String username
    ) {}
}

// Enable in configuration
@Configuration
@EnableConfigurationProperties(AppProperties.class)
public class AppConfig {}

// Usage
@Service
public class MyService {
    private final AppProperties props;

    public MyService(AppProperties props) {
        this.props = props;
    }
}

# application.yml
app:
  name: my-application
  timeout: 30s
  database:
    host: localhost
    port: 5432
    username: admin

Profiles

# application.yml (default)
spring:
  profiles:
    active: dev

---
spring:
  config:
    activate:
      on-profile: dev
server:
  port: 8080
logging:
  level:
    root: DEBUG

---
spring:
  config:
    activate:
      on-profile: prod
server:
  port: 80
logging:
  level:
    root: INFO

// Profile-specific beans
@Configuration
@Profile("dev")
public class DevConfig {
    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
            .setType(EmbeddedDatabaseType.H2)
            .build();
    }
}

@Configuration
@Profile("prod")
public class ProdConfig {
    @Bean
    public DataSource dataSource(DataSourceProperties props) {
        return DataSourceBuilder.create()
            .url(props.getUrl())
            .username(props.getUsername())
            .password(props.getPassword())
            .build();
    }
}

Bean Lifecycle

@Component
public class MyComponent implements InitializingBean, DisposableBean {

    @PostConstruct
    public void init() {
        // Called after dependency injection
    }

    @Override
    public void afterPropertiesSet() {
        // Called after properties set
    }

    @PreDestroy
    public void cleanup() {
        // Called before destruction
    }

    @Override
    public void destroy() {
        // Called on shutdown
    }
}

// Or with @Bean
@Bean(initMethod = "init", destroyMethod = "cleanup")
public MyService myService() {
    return new MyService();
}

Best Practices

1. Use @ConfigurationProperties over @Value for type-safe configuration
2. Profiles for environment-specific config, not feature flags
3. Externalize configuration - never hardcode secrets
4. Use record classes for immutable configuration properties
5. Validate configuration with @Validated and Jakarta constraints
6. Auto-configuration order matters - use @AutoConfigureAfter/@AutoConfigureBefore

References

• Auto-Configuration - Custom auto-config, conditions
• Configuration Properties - Binding, validation, relaxed binding

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