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Aporeon

Technical interview practice, from one developer to another.

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Java & Spring Backend

Spring Core & Boot

Dependency injection, bean lifecycle and scope, configuration, auto-configuration, application startup, and framework boundaries.

24 drillsPractice one at a timeOrdered pathComparison questionConcept questionArchitecture scenarioDebugging scenario

Recommended start

Spring vs Spring Boot

Separates Spring's application framework and container from Boot's opinionated startup, dependency, configuration, and operational conventions.

Easy~5 minStep 1 of 24

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1Spring vs Spring BootRecommended startSeparates Spring's application framework and container from Boot's opinionated startup, dependency, configuration, and operational conventions.Comparison questionEasy~5 minJavaSpring BootPractice 2

Practice order

24 drillsOne at a time

1Spring vs Spring BootUp next / Easy / ~5 min
2IoC and DI in SpringEasy / ~5 min
3Spring injection stylesMedium / ~7 min

IoC and DI in Spring

Explains container ownership, dependency declarations, bean creation, and why dependency injection is a specific form of inversion of control.

Concept questionEasy~5 minJavaSpring Boot

Practice

3Spring injection stylesPrefers constructor injection for required dependencies while explaining the limited roles and costs of setter and field injection.Comparison questionMedium~7 minJavaSpring BootPractice

4Scanning vs explicit beansChooses stereotype scanning for owned application components and explicit factory methods for third-party types, construction policy, and visible composition.Comparison questionMedium~7 minJavaSpring BootPractice

5ApplicationContextExplains configuration loading, bean-definition processing, dependency resolution, lifecycle, events, resources, and environment access.Concept questionMedium~7 minJavaSpring BootPractice

6Spring bean lifecycleWalks from instantiation and dependency injection through post-processing, initialization callbacks, use, and supported destruction behavior.Concept questionMedium~7 minJavaSpring BootPractice

7Spring bean scopesExplains singleton, prototype, request, session, application, and WebSocket scopes as container lifecycle policies.Concept questionMedium~7 minJavaSpring BootPractice

8Singleton bean thread safetySeparates container instance reuse from concurrency guarantees and designs singleton services around stateless or safely coordinated state.Concept questionMedium~7 minJavaSpring BootPractice

9Shorter scope in singletonExplains why ordinary injection resolves once and chooses providers, factories, scoped proxies, or explicit parameters for shorter-lived dependencies.Architecture scenarioHard~10 minJavaSpring BootPractice

10Spring circular dependenciesTreats a bean cycle as a design signal, explains constructor failure, and uses delayed resolution only for genuine lifecycle boundaries.Debugging scenarioHard~10 minJavaSpring BootPractice

11Spring proxies and self-invocationExplains proxy interception, target delegation, JDK versus class proxies, method limits, and the self-invocation boundary.Concept questionHard~10 minJavaSpring BootPractice

12Scan boundaries and packagesPlaces the application class above owned components, uses capability-oriented packages, and keeps scanning and imports deliberate.Architecture scenarioMedium~7 minJavaSpring BootPractice

13ConfigurationProperties vs ValueUses typed grouped binding and validation for application configuration while reserving @Value for small isolated expressions.Comparison questionMedium~7 minJavaSpring BootPractice

14Property source precedenceExplains ordered property sources, profile documents, environment overrides, command-line values, and evidence-driven diagnosis.Concept questionHard~10 minJavaSpring BootPractice

15Profiles vs conditionsUses profiles for named environment or deployment groups and focused conditions for feature or capability selection.Comparison questionMedium~7 minJavaSpring BootPractice

16Boot auto-configurationExplains imported configuration classes, classpath and bean conditions, ordered defaults, back-off, and the condition report.Concept questionHard~10 minJavaSpring BootPractice

17Conditional beansUses class, bean, property, resource, and application conditions to provide explicit defaults without ambiguous registration.Concept questionHard~10 minJavaSpring BootPractice

18Starters and dependency managementSeparates dependency bundles, tested version alignment, transitive dependencies, and runtime auto-configuration.Concept questionMedium~7 minJavaSpring BootPractice

19Override Boot defaultsUses supported properties, replacement beans, and narrow exclusions in that order, with condition-report and upgrade verification.Architecture scenarioHard~10 minJavaSpring BootPractice

20Validate startup configurationBinds related values to typed configuration properties, applies validation constraints, and fails with actionable non-secret diagnostics.Architecture scenarioMedium~7 minJavaSpring BootPractice

21Boot startup hooksChooses hooks by application readiness phase and keeps migrations, warm-up, listeners, and background resources owned and observable.Comparison questionHard~10 minJavaSpring BootPractice

22Lazy initializationBalances faster startup and unused-bean avoidance against delayed failures, first-request latency, memory growth, and readiness semantics.Comparison questionHard~10 minJavaSpring BootPractice

23Diagnose bean resolutionTraces the injection point, candidate type, registration path, conditions, profiles, generics, qualifiers, and package boundaries.Debugging scenarioHard~10 minJavaSpring BootPractice

24Diagnose Boot startupPreserves the root cause, separates binding, bean, port, classpath, migration, and external failures, and uses Boot's diagnostic reports.Debugging scenarioHard~10 minJavaSpring BootPractice

4

Scanning vs explicit beans

Medium / ~7 min

5ApplicationContextMedium / ~7 min

6Spring bean lifecycleMedium / ~7 min

7Spring bean scopesMedium / ~7 min

8Singleton bean thread safetyMedium / ~7 min

+16 more drills in this section

Spring Core & Boot - Java & Spring Backend | Aporeon