Spring Boot Interview Questions You Actually Face in Real Projects

(With Real Answers & Follow-Up Questions)

Most Spring Boot interviews are not Q&A sessions. They are conversations.

You answer one question → interviewer digs deeper → tests whether you actually used Spring Boot in production.

Let’s go through real questions, strong answers, and typical follow-ups.

1️⃣ How Is Spring Boot Different From Spring Framework?

✅ Real Interview Answer

In Spring Framework, we manually configure most things like data sources, view resolvers, and server setup.

Spring Boot simplifies this by using auto-configuration, starter dependencies, and embedded servers, which reduces boilerplate and speeds up development.

In real projects, Spring Boot helps teams focus on business logic instead of configuration.

🔍 Follow-Up Questions

Q1: Can we do everything in Spring Boot that we do in Spring? ➡️ Answer: Yes. Spring Boot is built on top of Spring. It doesn’t remove flexibility.

Q2: Can auto-configuration be disabled? ➡️ Answer: Yes, using exclude in @SpringBootApplication or @EnableAutoConfiguration.

2️⃣ What Happens When You Run a Spring Boot Application?

✅ Real Interview Answer

When we run a Spring Boot app, SpringApplication.run() creates the application context, performs component scanning, applies auto-configuration, and starts the embedded server like Tomcat.

🔍 Follow-Up Questions

Q1: What is the role of @SpringBootApplication? ➡️ It combines:

• @Configuration
• @EnableAutoConfiguration
• @ComponentScan

Q2: How does Spring Boot know which beans to create automatically? ➡️ By checking classpath dependencies and conditional annotations.

3️⃣ What Is Spring Boot Auto-Configuration?

✅ Real Interview Answer

Auto-configuration means Spring Boot automatically configures beans based on dependencies present in the classpath and application properties.

For example, if spring-boot-starter-data-jpa is present, Spring Boot auto-configures:

• DataSource
• EntityManager
• TransactionManager

🔍 Follow-Up Questions

Q1: Where is auto-configuration logic written? ➡️ In spring.factories (older) / AutoConfiguration.imports (newer versions)

Q2: Which annotations control auto-configuration? ➡️ @ConditionalOnClass, @ConditionalOnBean, @ConditionalOnProperty

4️⃣ Have You Faced Application Startup Failures?

✅ Real Interview Answer

Yes, mostly due to missing beans, circular dependencies, or multiple bean definitions of the same type.

Typical fixes:

• Add missing annotations
• Use @Qualifier
• Use @Primary

🔍 Follow-Up Questions

Q1: How do you debug startup issues? ➡️ Enable debug logs:

debug=true

Q2: What is circular dependency? ➡️ Two beans depending on each other during initialization.

5️⃣ How Do You Handle Exceptions in REST APIs?

✅ Real Interview Answer

We use @ControllerAdvice to handle exceptions globally and return meaningful HTTP responses instead of stack traces.

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.NOT_FOUND)
                .body(ex.getMessage());
    }
}

🔍 Follow-Up Questions

Q1: Difference between @ExceptionHandler and @ControllerAdvice? ➡️ @ExceptionHandler is local; @ControllerAdvice is global.

Q2: How do you customize error response structure? ➡️ Create a custom error DTO.

6️⃣ How Does @Transactional Work?

✅ Real Interview Answer

*@Transactional works using AOP proxies. The transaction starts before the method execution and commits or rolls back after completion.*

Important rule:

Self-invocation does not trigger transactions.

🔍 Follow-Up Questions

Q1: Why does self-invocation fail? ➡️ Because calls don’t go through the proxy.

Q2: What are propagation types? ➡️ REQUIRED, REQUIRES_NEW, MANDATORY, etc.

7️⃣ How Do You Validate Incoming API Requests?

✅ Real Interview Answer

We use Bean Validation with annotations like @NotNull, @Size, and @Email, along with @Valid in controller methods.

🔍 Follow-Up Questions

Q1: Where do validation errors go? ➡️ They throw MethodArgumentNotValidException

Q2: How do you return custom validation messages? ➡️ Using @ControllerAdvice

8️⃣ Difference Between @Component, @Service, and @Repository?

✅ Real Interview Answer

Functionally they are the same, but they indicate intent:

• @Repository → Data access + exception translation
• @Service → Business logic
• @Component → Generic bean

🔍 Follow-Up Questions

Q1: What is exception translation? ➡️ Converts JDBC exceptions into Spring’s DataAccessException.

9️⃣ How Do You Manage Configurations for Multiple Environments?

✅ Real Interview Answer

We use Spring Profiles like dev, qa, and prod with separate property files and environment variables.

🔍 Follow-Up Questions

Q1: How do you activate a profile? ➡️ spring.profiles.active=prod

Q2: How do you manage secrets? ➡️ Environment variables or config server (never hardcode).

🔟 How Do You Monitor a Spring Boot Application?

✅ Real Interview Answer

We use Spring Boot Actuator to expose health, metrics, and application info endpoints.

🔍 Follow-Up Questions

Q1: Which endpoints are commonly used? ➡️ /health, /metrics, /info

Q2: How do you restrict actuator access? ➡️ Using Spring Security.

1️⃣1️⃣ How Do You Secure REST APIs?

✅ Real Interview Answer

We use Spring Security with JWT for stateless authentication and role-based authorization.

🔍 Follow-Up Questions

Q1: Why JWT instead of sessions? ➡️ REST APIs should be stateless.

Q2: Where do you store JWT? ➡️ On client side (usually in headers).

1️⃣2️⃣ Performance Issues You Faced in Spring Boot?

✅ Real Interview Answer

Common issues include N+1 queries, large payloads, and slow database calls.

Solutions:

• Pagination
• Caching
• Query optimization

🔍 Follow-Up Questions

Q1: How do you detect N+1 problem? ➡️ SQL logs + monitoring tools.

Q2: What caching options have you used? ➡️ Spring Cache with Redis or Ehcache.

🎯 Final Interview Tip (Very Important)

Always answer like this:

“In one of my projects…”

Interviewers don’t want perfect theory — they want proof that you’ve solved real problems.