10 Spring Boot Interview Questions (Pune Java, 2026)

The list

1. 1

   What is Spring Boot auto-configuration and how does it work?

   Auto-configuration applies sensible defaults based on classpath dependencies — add spring-boot-starter-data-jpa and you get DataSource + EntityManager + transaction manager without writing config.

   Why it matters: Asked at ~80% of Pune Spring Boot fresher rounds. Mention @EnableAutoConfiguration + spring.factories + conditional annotations like @ConditionalOnMissingBean for senior-fresher signal.

   Best for: First-pass interview screening question; expected to know cold.

2. 2

   Constructor injection vs @Autowired field injection — which is better?

   Constructor injection is the modern preference: immutable dependencies, fails fast at startup if missing, materially easier to unit test (no reflection required).

   Why it matters: Asked at ~60% of Pune rounds. Mention final fields + Lombok @RequiredArgsConstructor as the idiomatic 2026 pattern.

   Best for: Demonstrating modern best-practice awareness.

3. 3

   What's the difference between @Component, @Service, @Repository, and @Controller?

   All are specialisations of @Component (each makes the class a Spring-managed bean). Semantic differences: @Service = business-logic, @Repository = data-access (adds JPA exception translation), @Controller = web layer (with @RestController = @Controller + @ResponseBody).

   Why it matters: Asked at ~70% of Pune rounds. The exception-translation behaviour of @Repository is the differentiator that signals senior-fresher awareness.

   Best for: Foundation Spring Boot architecture question.

4. 4

   Explain Spring Boot REST API design with @RequestMapping variants.

   @GetMapping / @PostMapping / @PutMapping / @PatchMapping / @DeleteMapping are method-specific shortcuts for @RequestMapping(method = X). @PathVariable extracts URL segments, @RequestParam handles query params, @RequestBody deserialises JSON.

   Why it matters: Walk through a complete CRUD controller verbally; interviewers want to see fluency, not memorised syntax.

   Best for: Hands-on REST round; often asked alongside live coding.

5. 5

   How do you handle exceptions in Spring Boot REST APIs?

   @ControllerAdvice + @ExceptionHandler centralises exception handling. Map custom exceptions to ResponseEntity with appropriate HTTP status + error body. Mention Problem Details (RFC 7807) for modern API responses.

   Why it matters: Asked at ~55% of Pune product company rounds. Generic 500 errors signal weak engineering thinking; structured error responses signal production readiness.

   Best for: Differentiating beyond services-major fresher tier.

6. 6

   What's the N+1 query problem in JPA and how do you fix it?

   Fetching a list of N parent entities then accessing a related child triggers 1 query for the list + N queries for the children = N+1 total queries. Fix: eager fetching via JOIN FETCH in JPQL, @EntityGraph annotations, or batch fetching configuration.

   Why it matters: Asked at ~50% of Pune product company rounds; rare at services-major fresher tier but signals senior-fresher awareness when raised proactively.

   Best for: Strong signal at product-company interviews; differentiates from pure-CRUD candidates.

7. 7

   Explain @Transactional and its propagation behaviours.

   @Transactional starts a database transaction around the annotated method (auto-rollback on RuntimeException, commit on normal return). Propagation REQUIRED (default) joins existing transaction or creates one; REQUIRES_NEW always creates a new one; SUPPORTS uses one if present; NESTED creates a savepoint.

   Why it matters: Asked at ~45% of Pune rounds. Mention common pitfall: self-invocation doesn't trigger proxying (the AOP advice is on the proxy, not the bean itself).

   Best for: Transactional integrity question; common in BFSI-targeted interviews.

8. 8

   How do you secure a Spring Boot REST API?

   Spring Security with stateless JWT authentication is the modern default. Filter chain configuration via SecurityFilterChain bean: disable CSRF for REST APIs, require authentication on protected endpoints, use BCryptPasswordEncoder for password hashing, write a custom OncePerRequestFilter for JWT parsing.

   Why it matters: Asked at ~60% of Pune rounds including services majors. Spring Security 6 + Lambda DSL is the 2026 pattern; older XML config knowledge is unnecessary.

   Best for: Architecture-tier question; demonstrates production-readiness thinking.

9. 9

   What testing strategy do you use for Spring Boot apps?

   Three-layer pyramid: JUnit 5 + Mockito unit tests on service logic, @WebMvcTest for controller layer (mocking services), @DataJpaTest for repository layer (in-memory H2 or Testcontainers). Mention Testcontainers for integration tests against real PostgreSQL — the modern Pune product-company pattern.

   Why it matters: Asked at ~55% of Pune rounds. Services majors check awareness; product companies probe depth + idiomatic patterns.

   Best for: Demonstrating professional engineering discipline.

10. 10

    How do you externalise configuration in Spring Boot?

    application.yml or application.properties with profile-specific variants (application-dev.yml, application-prod.yml). Use @Value for single properties, @ConfigurationProperties for grouped + type-safe binding. Sensitive values (DB passwords, API keys) load from environment variables or Spring Cloud Config + Vault in production.

    Why it matters: Asked at ~40% of Pune rounds. Mention 12-factor app principles + never committing secrets to git for senior-fresher signal.

    Best for: Configuration management round; common at DevOps-leaning interviews.

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