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intermediate Phase · Spring Boot Fundamentals

Component Scanning

Understand how Spring discovers and registers components.

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Component Scanning

How Component Scanning Works

com.example.app/           ← @SpringBootApplication here
├── controller/             ← Scanned ✓
│   └── ProductController
├── service/                ← Scanned ✓
│   └── ProductService
├── repository/             ← Scanned ✓
│   └── ProductRepository
└── util/                   ← Scanned ✓
    └── Helper

What Gets Scanned

Annotation Package Purpose
@Component Any Generic Spring-managed component
@Service Service layer Business logic
@Repository Data layer Database access
@Controller Web layer MVC controllers
@RestController Web layer REST API controllers
@Configuration Config Bean definitions

Custom Scan Paths

@SpringBootApplication
@ComponentScan(basePackages = "com.example.core")
public class Application { }

Filtering

@ComponentScan(
    basePackages = "com.example",
    includeFilters = @ComponentScan.Filter(
        type = FilterType.ANNOTATION,
        classes = CustomAnnotation.class
    ),
    excludeFilters = @ComponentScan.Filter(
        type = FilterType.ASSIGNABLE_TYPE,
        classes = TestHelper.class
    )
)

Spring Best Practices

Configuration

  • Use properties over YAML for simple configs
  • Externalize configuration
  • Use profiles for environments
  • Validate on startup

Bean Management

  • Prefer constructor injection
  • Use appropriate scope
  • Implement lazy initialization
  • Clean up resources

Security

  • Use Spring Security
  • Implement CSRF protection
  • Use method-level security
  • Log security events

Key Points

  • Understanding Component Scanning is essential for production systems
  • Always consider scalability and maintainability
  • Test thoroughly before deploying to production
  • Monitor performance and set up alerting

Common Patterns

  1. Validation: Always validate input at the boundary
  2. Error Handling: Use structured error responses
  3. Logging: Log key events for debugging
  4. Testing: Unit, integration, and load tests
  5. Documentation: Keep docs updated with code changes

Practice Problems

0 / 3 solved
Implement Component Scanning

Design and implement a solution for Component Scanning in a backend system. Consider scalability, error handling, and production readiness.

Solution 
// Component Scanning implementation
// Key aspects: validation, error handling, logging, testing

public class ComponentScanning {
    // Production-ready implementation
}
Component Scanning Edge Cases

Identify and handle edge cases for Component Scanning. What happens under high load, with invalid input, or during failures?

Solution 
// Edge case handling:
// 1. Null/empty input -> validation
// 2. High load -> rate limiting, queuing
// 3. Failures -> retries, circuit breaker
// 4. Concurrent access -> locks, idempotency
Component Scanning Testing Strategy

Write a testing strategy for Component Scanning. Include unit tests, integration tests, and performance tests.

Solution 
// Test plan:
// - Unit: 80% coverage target
// - Integration: API contracts
// - Performance: latency, throughput
// - Chaos: failure injection

Quiz

1. Where does component scanning start by default?

Question 1 options

2. Which annotation is a specialization of @Component for services?

Question 2 options

3. What is a common mistake when implementing Component Scanning?

Question 3 options

Flashcards

Question

Where does component scanning start?

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Answer

Package of @SpringBootApplication class + all sub-packages

Question

Stereotype annotations for components?

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Answer

@Component, @Service, @Repository, @Controller, @RestController

Question

Component Scanning best practices

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Answer

Follow SOLID principles, write clean code, test thoroughly, document decisions, and monitor in production.

Revision Notes

Key Takeaways

  • 1. Component scanning starts from @SpringBootApplication package
  • 2. Stereotype annotations: @Component, @Service, @Repository, @Controller
  • 3. Custom scan paths with @ComponentScan(basePackages)
  • 4. All sub-packages are scanned automatically

Interview Tips

  • • Explain component scanning behavior
  • • Know stereotype annotations

Cheat Sheet

Component Scanning

  • Start: Package of @SpringBootApplication
  • Scope: All sub-packages
  • Stereotypes: @Component, @Service, @Repository, @Controller
  • Custom: @ComponentScan(basePackages = "...")