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Spring Boot Backend Interview Roadmap

🎯 Phase 1: Java Fundamentals (2-3 weeks)​

Core Java Concepts​

  • OOP Principles: Inheritance, Encapsulation, Polymorphism, Abstraction
  • Collections Framework: List, Set, Map, Queue implementations and when to use each
  • Exception Handling: Checked vs unchecked exceptions, custom exceptions
  • Multithreading: Thread lifecycle, synchronization, concurrent collections
  • Memory Management: Heap vs Stack, Garbage Collection, Memory leaks
  • Java 8+ Features: Lambda expressions, Stream API, Optional, Method references
  • Generics: Wildcards, bounded types, type erasure

Interview Focus Areas​

  • Time/Space complexity analysis
  • Design patterns (Singleton, Factory, Observer, Strategy)
  • SOLID principles
  • Functional programming concepts

🚀 Phase 2: Spring Framework Basics (3-4 weeks)​

Core Spring Concepts​

  • Inversion of Control (IoC): Dependency injection principles
  • Application Context: Bean lifecycle, scopes, configuration
  • Annotations: @Component, @Service, @Repository, @Controller
  • Configuration: Java-based vs XML vs Annotation-based
  • AOP (Aspect-Oriented Programming): Cross-cutting concerns, proxies

Spring Boot Fundamentals​

  • Auto-configuration: How Spring Boot works under the hood
  • Starter Dependencies: Common starters and their purposes
  • Application Properties: Configuration management, profiles
  • Main Application Class: @SpringBootApplication annotation breakdown
  • Component Scanning: Package structure best practices

Key Interview Topics​

  • Bean creation process and circular dependencies
  • Different ways to inject dependencies
  • Spring Boot vs Spring Framework differences
  • Auto-configuration magic explanation

🗄️ Phase 3: Database Integration (2-3 weeks)​

Spring Data JPA​

  • Entity Mapping: @Entity, @Table, @Column, @Id annotations
  • Relationships: @OneToOne, @OneToMany, @ManyToMany, @JoinColumn
  • Repository Pattern: JpaRepository, CrudRepository, custom repositories
  • Query Methods: Derived queries, @Query annotation, native queries
  • Pagination and Sorting: Pageable interface, Sort parameters

Database Concepts​

  • Transaction Management: @Transactional, ACID properties, isolation levels
  • Connection Pooling: HikariCP configuration, connection management
  • Database Migration: Flyway, Liquibase for version control
  • N+1 Problem: Lazy vs Eager loading, @EntityGraph

Interview Scenarios​

  • Handling database connections in high-traffic applications
  • Query optimization strategies
  • Database schema design for scalability
  • Transaction rollback scenarios

🌐 Phase 4: RESTful Web Services (2-3 weeks)​

REST API Development​

  • HTTP Methods: GET, POST, PUT, DELETE, PATCH semantics
  • Status Codes: Proper usage of 2xx, 4xx, 5xx codes
  • Request Mapping: @RestController, @RequestMapping, @PathVariable
  • Request/Response Handling: @RequestBody, @ResponseBody, ResponseEntity
  • Validation: @Valid, @NotNull, @Size, custom validators

Advanced REST Concepts​

  • HATEOAS: Hypermedia implementation with Spring
  • Content Negotiation: Accept headers, multiple response formats
  • Versioning Strategies: URL, header, parameter-based versioning
  • Error Handling: @ExceptionHandler, @ControllerAdvice, global error handling

API Documentation​

  • OpenAPI/Swagger: Auto-generating documentation
  • API Design: Resource naming, URI patterns, RESTful principles

🔒 Phase 5: Security Implementation (2-3 weeks)​

Spring Security​

  • Authentication: Username/password, JWT, OAuth2
  • Authorization: Role-based access control, method-level security
  • Security Configuration: SecurityConfig, WebSecurityConfigurerAdapter
  • Password Encoding: BCrypt, security best practices
  • CSRF Protection: Configuration and exception handling

JWT Implementation​

  • Token Generation: Claims, expiration, signing
  • Token Validation: Middleware, filter chains
  • Refresh Tokens: Implementation strategies
  • Security Headers: CORS, XSS protection

Interview Security Topics​

  • Common security vulnerabilities (OWASP Top 10)
  • Session management strategies
  • API rate limiting implementation
  • Secure coding practices

⚡ Phase 6: Performance & Scalability (2-3 weeks)​

Caching Strategies​

  • Spring Cache: @Cacheable, @CacheEvict, cache providers
  • Redis Integration: Configuration, clustering, persistence
  • Cache Patterns: Cache-aside, write-through, write-behind
  • Distributed Caching: Consistency, eviction policies

Asynchronous Processing​

  • @Async: Thread pool configuration, exception handling
  • Message Queues: RabbitMQ, Apache Kafka integration
  • Event-Driven Architecture: ApplicationEvent, @EventListener
  • Batch Processing: Spring Batch for large data processing

Monitoring and Observability​

  • Actuator Endpoints: Health checks, metrics, info endpoints
  • Logging: Logback, log levels, structured logging
  • Metrics: Micrometer, custom metrics, APM tools
  • Distributed Tracing: Sleuth, Zipkin integration

🧪 Phase 7: Testing Strategies (2 weeks)​

Testing Frameworks​

  • Unit Testing: JUnit 5, Mockito, test slices
  • Integration Testing: @SpringBootTest, TestContainers
  • Web Layer Testing: MockMvc, WebMvcTest
  • Repository Testing: @DataJpaTest, embedded databases

Testing Best Practices​

  • Test Pyramid: Unit, integration, end-to-end testing ratios
  • Mocking Strategies: When to mock vs real implementations
  • Test Data Management: Fixtures, builders, factories
  • Code Coverage: Tools and meaningful coverage metrics

🏗️ Phase 8: Advanced Topics (3-4 weeks)​

Microservices Architecture​

  • Service Discovery: Eureka, Consul integration
  • API Gateway: Spring Cloud Gateway, routing, filtering
  • Circuit Breakers: Hystrix, Resilience4j for fault tolerance
  • Distributed Configuration: Spring Cloud Config Server
  • Load Balancing: Client-side vs server-side strategies

DevOps Integration​

  • Containerization: Docker, creating efficient images
  • Cloud Deployment: AWS, Azure, GCP specific services
  • CI/CD Pipelines: Jenkins, GitHub Actions, deployment strategies
  • Environment Management: Configuration per environment

Advanced Spring Features​

  • Custom Auto-configuration: Creating starter modules
  • Conditional Beans: @ConditionalOnProperty, custom conditions
  • Health Indicators: Custom health checks
  • Actuator Custom Endpoints: Monitoring and management

📚 Interview Preparation Strategy​

System Design Practice​

  • Database Design: E-commerce, social media, chat applications
  • API Design: RESTful services, GraphQL considerations
  • Scalability Patterns: Load balancing, caching, database sharding
  • Real-world Scenarios: Handling high traffic, data consistency

Coding Challenges​

  • Algorithm Problems: Data structures, searching, sorting
  • Spring-specific Scenarios: Custom validation, error handling
  • Database Queries: Complex JPA queries, performance optimization
  • Design Pattern Implementation: Factory, Strategy, Observer patterns

Mock Interview Topics​

  • Architecture Decisions: Why Spring Boot over alternatives?
  • Performance Tuning: Identifying bottlenecks, optimization strategies
  • Troubleshooting: Common issues and debugging approaches
  • Best Practices: Code organization, error handling, security

🎯 Timeline Summary (16-20 weeks total)​

Beginner Level (0-1 years): Focus heavily on Phases 1-4 Intermediate Level (1-3 years): Cover all phases with emphasis on 5-7 Senior Level (3+ years): Deep dive into Phase 8 and system design

🔧 Hands-on Projects​

  1. E-commerce REST API: Product catalog, user management, order processing
  2. Blog Platform: CRUD operations, authentication, file upload
  3. Task Management System: Real-time updates, notifications, scheduling
  4. Microservices Demo: Multiple services with inter-service communication

📖 Recommended Resources​

Books​

  • "Spring Boot in Action" by Craig Walls
  • "Spring in Action" by Craig Walls
  • "Effective Java" by Joshua Bloch

Online Platforms​

  • Spring.io official documentation
  • Baeldung tutorials
  • LeetCode for algorithm practice
  • System Design Primer on GitHub

Practice Platforms​

  • HackerRank, CodeSignal for coding challenges
  • Pramp, InterviewBit for mock interviews
  • GitHub for portfolio projects

✅ Interview Readiness Checklist​

  • Can explain Spring Boot auto-configuration
  • Implement JWT authentication from scratch
  • Design database schema for complex relationships
  • Handle high-concurrency scenarios
  • Implement caching strategies
  • Create comprehensive test suites
  • Deploy applications using Docker
  • Debug performance issues
  • Design RESTful APIs following best practices
  • Implement security measures against common vulnerabilities

Remember: Consistent practice and building real projects is more valuable than just theoretical knowledge. Focus on understanding the "why" behind each concept, not just the "how."