Top 10 Spring Boot Real-Time Interview Questions – From Project Scenarios
Spring Boot is widely used in real-world Java backend development. Interviewers love asking scenario-based questions to check if you have hands-on experience or just theoretical knowledge. Here's a hand-picked list of real-time Spring Boot questions asked in interviews for 1–3 years experienced developers.
Q1. How did you implement REST APIs in Spring Boot?
Answer: We used @RestController with @GetMapping, @PostMapping annotations. DTOs were used for request/response. We used ResponseEntity for full HTTP response control.
Q2. How did you handle exceptions globally?
Answer: We created a class annotated with @ControllerAdvice and used @ExceptionHandler methods. For example, we returned custom error JSON when a record was not found.
Q3. How do you use @Value, profiles, and configuration in your project?
Answer: We externalized environment configs using application-dev.properties and @Value to inject them. We activated profiles using spring.profiles.active and managed secrets using encrypted vault keys.
Q4. How did you write unit tests for services/controllers?
Answer: We used JUnit 5 with Mockito. For controller tests, @WebMvcTest was used with mock services. For service layer, we mocked repository calls.
Q5. How do you manage DTO and entity separation?
Answer: We never exposed JPA entities directly. DTOs were mapped using ModelMapper and sometimes manually for custom logic. This helped in avoiding lazy loading issues and keeping API payloads clean.
Q6. What challenges did you face with DB or JPA?
Answer: We faced LazyInitializationException, solved it using @Transactional or fetching required fields via joins. Also handled N+1 queries using @EntityGraph and optimized queries using JPQL.
Q7. Did you use caching, and why?
Answer: Yes, for read-heavy endpoints like product listings. We used @Cacheable and configured EhCache. It reduced DB hits significantly.
Q8. How do you secure your endpoints?
Answer: We used Spring Security with JWT tokens. For public endpoints like login and register, we excluded paths. Role-based access was implemented using @PreAuthorize.
Q9. How do you handle file uploads?
Answer: We used MultipartFile in request and stored files temporarily on server or forwarded to AWS S3. Size limits and validations were handled using spring.servlet.multipart.* properties.
Q10. How do you deploy Spring Boot apps in real life?
Answer: We build a fat JAR using Maven and deploy it on cloud VM (Linux with Java 17). We use systemd for process management and configured logs to rotate using logback + cron.
✅ Bonus Tips:
- Always explain what YOU implemented, not the team
- Mention tools: Postman, Git, Jenkins, Sonar if used
- Give project-based answers, not textbook ones
📅 Last Updated: 19 May 2025
📎 #SpringBootRealTime #JavaBackendInterview #MicroservicesPrep #SpringBoot2025
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