Practice Spring Boot interview questions on auto-configuration, dependency injection, API validation and testing, with a failing-startup scenario. Start with the question, explain the mechanism, and then state an assumption or tradeoff. The scenarios below are original practice examples, not questions supplied by an employer.
What does Spring Boot auto-configuration do?
It supplies configuration when conditions such as available dependencies and missing application beans match. It reduces repetitive setup; it does not remove the need to understand the resulting application. If you define your own bean, an applicable default may back off. In an interview, distinguish the mechanism from the convenience: explain which dependency or bean changed, then investigate the condition report rather than guessing that an annotation fixes everything.
Why choose constructor injection?
A constructor makes required dependencies visible and supports creating the object directly in a unit test. A service receiving a repository and a clock is easier to test than one that reaches into global state. Keep the number of dependencies meaningful: a long constructor may reveal too many responsibilities. Explain how you would separate those responsibilities before choosing an injection style solely to hide the parameter list.
How would you validate a REST request?
Separate malformed input from a valid request that violates a business rule. Validate required fields and basic formats at the boundary, then enforce business constraints where the operation is owned. Return a consistent error structure with useful field information without exposing internal exceptions. Discuss duplicate requests and concurrent updates separately; checking a value once at the controller does not guarantee that it remains valid when the database changes.
What belongs in a unit test versus an integration test?
Test a price calculation as ordinary Java code with small deterministic inputs. Test HTTP serialization, dependency wiring and persistence behavior at the integration boundary they depend on. A test loading the entire application for every arithmetic case is expensive and may obscure the failure. Conversely, mocking every persistence detail cannot prove that the real mapping or transaction works. Describe the behavior each layer is meant to verify.
How do you diagnose a startup configuration failure?
Read the earliest relevant cause, identify the bean or property involved, and compare the failing environment with a working one. Check profile selection, configuration sources and dependency compatibility. Use the auto-configuration condition report when a default did or did not apply. Avoid changing several settings at once: propose a small testable explanation, make one change, and verify both startup and the affected endpoint.
Worked example
Original scenario: a service starts locally but fails in a deployment because no database connection can be created. First establish whether the production profile is selected and whether the expected property names exist. Inspect values safely without printing secrets. Then check connectivity and the driver dependency.
A strong answer does not assume the database is down. It lists evidence that separates missing configuration, incorrect configuration and an unreachable dependency. After a fix, verify a database-backed operation and add a configuration check appropriate to deployment. Record the relevant framework version because configuration behavior can change between major releases.
Practice plan
Rehearse the five questions in ninety seconds each. Sketch a controller, service and repository for creating an order. Name one validation check at each boundary and one integration test that would catch incorrect wiring. Finish by explaining how you would investigate the same failure without access to production credentials.
Use Cluegent during preparation to review your own answer: ask for one incorrect assumption and one follow-up question, then respond again without suggestions. Check current plans before choosing a subscription. Follow the employer's rules during the actual interview.
Sources checked
These official references support the guide. Product details and technical documentation can change; check the linked source for current information.
Where Cluegent helps
Cluegent supports permitted live workflows with transcript context, typed prompts, screenshot-aware answers, resume context, custom response behavior, quick action buttons, and a private desktop overlay. It is most useful when you already understand the subject and need help staying structured under pressure.
Frequently asked questions
Are these questions suitable for experienced developers?
Yes. Extend each answer with a real failure, an observable diagnostic and a tradeoff. Definitions alone are usually insufficient for deeper follow-ups.
Should I memorize annotation names?
Know the annotations used in your own projects, but also explain what they enable and how you would verify the resulting behavior.