Spring Boot Internals and Interview Topic Checklist

Spring Core

• IoC
• Dependency Injection
• Constructor Injection
• Bean Lifecycle

Spring Boot

• Auto Configuration
• Starters
• Spring vs Spring Boot
• @SpringBootApplication

Spring MVC

• DispatcherServlet
• Filter vs Interceptor
• Global Exception Handling

JPA

• JPA vs Hibernate
• Entity Lifecycle
• Lazy vs Eager
• N+1 Problem
• JPQL vs Native Query
• @Query

Transactions

• @Transactional internals
• Propagation
• Isolation Levels

Application Startup

flowchart TD
A["SpringApplication.run()"] --> B[ApplicationContext Created]
B --> C[Auto Configuration]
C --> D[Component Scan]
D --> E[Bean Creation]
E --> F[Embedded Tomcat Starts]

@SpringBootApplication includes:

@Configuration
@EnableAutoConfiguration
@ComponentScan

Bean Lifecycle

flowchart TD
A[Instantiation] --> B[Dependency Injection]
B --> C["@PostConstruct"]
C --> D[Ready]
D --> E["@PreDestroy"]

Transaction Flow

flowchart TD
A[Client] --> B[Spring Proxy]
B --> C[Transaction Manager]
C --> D[Database]

Key Takeaways

• Spring Boot startup runs through ApplicationContext creation, auto configuration, component scanning, bean creation, then embedded server startup, in that order.
• @Transactional works through a Spring AOP proxy — this is why calls to @Transactional methods from within the same class (bypassing the proxy) don’t get transactional behavior.
• Use this list as a topic checklist alongside the Spring Boot Interview Questions and Answers guide for worked examples of each area.