spring-boot-patterns

Spring Boot Patterns

Core patterns for building production-ready Spring Boot applications.

When to Use

• User is setting up a Spring Boot project
• User asks about @Component, @Service, @Repository usage
• User needs dependency injection patterns
• User is configuring profiles for dev/staging/prod
• User asks about externalized configuration or actuator

Core Patterns

Stereotype Annotations -- Layer Separation

Use the correct annotation for each architectural layer. Spring applies different behaviors to each.

@Repository  // Data access -- translates persistence exceptions
public class UserRepository {
    private final JdbcTemplate jdbc;
    public UserRepository(JdbcTemplate jdbc) { this.jdbc = jdbc; }

    public Optional<User> findById(Long id) {
        return jdbc.query("SELECT * FROM users WHERE id = ?",
            new BeanPropertyRowMapper<>(User.class), id).stream().findFirst();
    }
}

@Service  // Business logic -- transactional boundaries live here
public class UserService {
    private final UserRepository userRepository;
    public UserService(UserRepository userRepository) { this.userRepository = userRepository; }

    @Transactional
    public User createUser(CreateUserRequest request) {
        return userRepository.save(new User(request.name(), request.email()));
    }
}

@RestController  // Web layer -- handles HTTP requests
@RequestMapping("/api/v1/users")
public class UserController {
    private final UserService userService;
    public UserController(UserService userService) { this.userService = userService; }

    @PostMapping
    @ResponseStatus(HttpStatus.CREATED)
    public UserResponse createUser(@Valid @RequestBody CreateUserRequest request) {
        return UserResponse.from(userService.createUser(request));
    }
}

Constructor Injection

Always use constructor injection. It makes dependencies explicit, supports immutability, and works with final fields. Avoid field injection with @Autowired.

@Service
public class OrderService {
    private final OrderRepository orderRepository;
    private final PaymentGateway paymentGateway;
    private final NotificationService notificationService;

    // Single constructor -- @Autowired is implicit, no annotation needed
    public OrderService(
            OrderRepository orderRepository,
            PaymentGateway paymentGateway,
            NotificationService notificationService) {
        this.orderRepository = orderRepository;
        this.paymentGateway = paymentGateway;
        this.notificationService = notificationService;
    }
}

Profiles -- Environment-Specific Configuration

Use profiles to swap implementations and configuration per environment.

# application.yml -- shared defaults
spring:
  application:
    name: my-service

---
# application-dev.yml
spring:
  datasource:
    url: jdbc:h2:mem:devdb
    driver-class-name: org.h2.Driver
  jpa:
    show-sql: true

---
# application-prod.yml
spring:
  datasource:
    url: jdbc:postgresql://${DB_HOST}:5432/${DB_NAME}
    username: ${DB_USER}
    password: ${DB_PASSWORD}
  jpa:
    show-sql: false

Profile-specific beans:

@Configuration
public class StorageConfig {

    @Bean
    @Profile("dev")
    public StorageService localStorageService() {
        return new LocalFileStorageService("/tmp/uploads");
    }

    @Bean
    @Profile("prod")
    public StorageService s3StorageService(S3Client s3Client) {
        return new S3StorageService(s3Client);
    }
}

@ConfigurationProperties -- Type-Safe Configuration

Bind external configuration to strongly-typed POJOs. Prefer this over scattered @Value annotations.

@ConfigurationProperties(prefix = "app.mail")
public record MailProperties(
    String host,
    int port,
    String fromAddress,
    Duration timeout,
    RetryProperties retry
) {
    public record RetryProperties(int maxAttempts, Duration delay) {}
}

app:
  mail:
    host: smtp.example.com
    port: 587
    from-address: noreply@example.com
    timeout: 5s
    retry:
      max-attempts: 3
      delay: 2s

Enable it:

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

Actuator -- Production Monitoring

Expose health checks, metrics, and application info for monitoring systems.

# application.yml
management:
  endpoints:
    web:
      exposure:
        include: health,info,metrics,prometheus
  endpoint:
    health:
      show-details: when-authorized
  health:
    db:
      enabled: true
    redis:
      enabled: true

Custom health indicator:

@Component
public class PaymentGatewayHealthIndicator implements HealthIndicator {
    private final PaymentGateway gateway;
    public PaymentGatewayHealthIndicator(PaymentGateway gateway) { this.gateway = gateway; }

    @Override
    public Health health() {
        try {
            return gateway.ping()
                ? Health.up().withDetail("gateway", "reachable").build()
                : Health.down().withDetail("gateway", "unreachable").build();
        } catch (Exception e) { return Health.down(e).build(); }
    }
}

Anti-Patterns

• Field injection with @Autowired -- Makes dependencies hidden, prevents immutability, and breaks testing. Use constructor injection instead.
• Business logic in controllers -- Controllers should only handle HTTP concerns (request parsing, response formatting). Delegate to services.
• Catching all exceptions in controllers -- Use @ControllerAdvice with @ExceptionHandler for centralized exception handling.
• Using @Component for everything -- Use the specific stereotype (@Service, @Repository, @Controller) so Spring applies the correct behavior (transaction proxies, exception translation).
• Hardcoding configuration values -- Use @ConfigurationProperties or environment variables. Never hardcode URLs, credentials, or environment-specific values.

Quick Reference

Stereotype annotations:
  @Component    -- Generic Spring-managed bean
  @Service      -- Business logic layer
  @Repository   -- Data access layer (exception translation)
  @Controller   -- Web layer (returns views)
  @RestController -- Web layer (returns JSON)

Configuration:
  @ConfigurationProperties  -- Type-safe config binding
  @Value("${key}")         -- Single value injection
  @Profile("dev")          -- Environment-specific bean

Actuator endpoints:
  /actuator/health    -- Application health
  /actuator/info      -- Application info
  /actuator/metrics   -- Micrometer metrics
  /actuator/prometheus -- Prometheus-format metrics