Beans

What Is a Spring Bean?

A bean is an object managed by the Spring IoC container. Any class annotated with Spring stereotypes becomes a bean.

Bean Scopes

Scope	Description	Use Case
singleton	One instance per container (default)	Stateless services
prototype	New instance each time	Stateful objects
request	One per HTTP request	Web apps
session	One per HTTP session	User sessions

Bean Lifecycle

1. Container creates bean instance
2. Dependencies injected
3. BeanNameAware.setBeanName()
4. BeanFactoryAware.setBeanFactory()
5. ApplicationContextAware.setApplicationContext()
6. @PostConstruct
7. InitializingBean.afterPropertiesSet()
8. Custom init-method
9. Bean ready for use
10. @PreDestroy
11. DisposableBean.destroy()
12. Custom destroy-method

Bean Definition

@Component  // Marks as Spring-managed bean
public class MyBean {
    // Spring creates and manages this
}

@Configuration
public class AppConfig {
    @Bean  // Explicit bean definition
    public MyBean myBean() {
        return new MyBean();
    }
}

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 Spring Beans 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