This is a playground for spring boot related projects.

• Spring concepts are arranged on a folder level context.

Topics will contain articles that either cover the entire concept or merge a few related together. To Explore this project ensure you have the Prerequisites, if not here is an article for the same. Using the latest version of java though

java --version # openjdk 25.0.4.1 2026-08-18

• Project Arrangment

0. Prerequisites

• Core Java (8/11/17/21): OOP, collections, generics, streams, lambdas, Optional
• Modern Java: records, sealed classes, pattern matching
• Concurrency basics: threads, ExecutorService, CompletableFuture
• Virtual threads (Java 21+)
• Build tools: Maven or Gradle
• Git and basic Linux/CLI
• HTTP, REST, JSON
• Basic SQL

1. Spring Core and Fundamentals

• Spring Framework fundamentals
• Inversion of Control (IoC)
• Dependency Injection (DI)
• Constructor vs setter vs field injection
• Spring Beans
• Bean scopes (Singleton, Prototype, Request, Session)
• Bean lifecycle
• ApplicationContext and BeanFactory
• Component scanning
• Stereotype annotations
  • @Component
  • @Service
  • @Repository
  • @Controller
• Java-based configuration (@Configuration, @Bean)
• @Qualifier, @Primary, @Lazy
• Profiles (@Profile)
• Properties and configuration management
• Spring Expression Language (SpEL)
• Conditional bean registration (@ConditionalOnProperty, @ConditionalOnClass)
• Auto-configuration
• Custom auto-configuration and custom starters
• Spring Boot starters
• Spring Initializr and project structure
• @SpringBootApplication
• Spring Boot application lifecycle
• CommandLineRunner and ApplicationRunner
• DevTools and hot reload
• Graceful shutdown

2. Spring Web (REST API Development)

• Spring MVC
• REST API development
• Controllers and request mappings
• @RestController
• @RequestMapping
• @GetMapping, @PostMapping, @PutMapping, @DeleteMapping, @PatchMapping
• Request parameters and path variables (@RequestParam, @PathVariable)
• @RequestHeader
• Request and response bodies (@RequestBody)
• ResponseEntity
• DTOs (Data Transfer Objects)
• DTO mapping (MapStruct, ModelMapper)
• Request validation
• Bean Validation (@Valid, @NotNull, @NotBlank, @Size)
• Custom validators
• Global exception handling (@ControllerAdvice, @ExceptionHandler)
• Custom exception handling
• ProblemDetail / RFC 7807 error responses
• HTTP status codes
• REST API design principles (Richardson maturity model)
• API versioning
• Pagination and sorting
• Filtering and searching
• File uploads and downloads
• Multipart requests
• Content negotiation
• Jackson serialization (@JsonProperty, @JsonIgnore, custom serializers)
• CORS configuration
• Interceptors and filters
• Servlet filters
• Async request processing
• Server-Sent Events (SSE)
• WebSockets and STOMP
• HATEOAS (optional)
• Thymeleaf / server-side rendering (optional)
• Spring WebFlux (reactive web development)

3. Spring Security (Authentication and Authorization)

• Spring Security architecture
• Authentication vs authorization
• Security filter chain
• SecurityFilterChain configuration (lambda DSL)
• UserDetails and UserDetailsService
• Password encoding (BCrypt, Argon2, DelegatingPasswordEncoder)
• Authentication providers
• Form login and HTTP Basic
• Role-based access control (RBAC)
• Authority-based access control
• Method-level security
• @PreAuthorize, @PostAuthorize, @Secured
• JWT authentication
• Refresh token mechanisms
• OAuth 2.0
• OpenID Connect (OIDC)
• OAuth2 Resource Server
• OAuth2 Client
• Social login
• Session-based authentication
• Stateless authentication
• Session management and session fixation
• Remember-me and logout
• CSRF protection
• CORS security
• XSS prevention
• Security headers
• API endpoint protection
• Custom authentication filters
• Custom authorization logic
• Integration with identity providers (Keycloak, Auth0, Okta)
• Multi-factor authentication basics
• Rate limiting and brute-force protection
• OWASP Top 10 awareness
• Testing secured endpoints (@WithMockUser, spring-security-test)

4. Spring Data and Database Management

• JDBC fundamentals
• Spring JDBC (JdbcTemplate, JdbcClient)
• Spring Data JPA
• Hibernate ORM
• Entity mapping (@Entity, @Id, @GeneratedValue)
• Entity relationships
  • One-to-One
  • One-to-Many
  • Many-to-One
  • Many-to-Many
• Entity lifecycle
• JPA repositories (JpaRepository, CrudRepository, PagingAndSortingRepository)
• Derived query methods
• JPQL
• Native SQL queries (@Query)
• Criteria API
• Specifications
• Projections (interface/DTO)
• Pagination and sorting
• Lazy and eager loading
• N+1 query problem
• Fetch joins and entity graphs
• Transactions
• @Transactional
• Transaction propagation
• Transaction isolation levels
• Rollback rules and common pitfalls (self-invocation, checked exceptions)
• Optimistic locking
• Pessimistic locking
• Database connection pooling (HikariCP)
• Database migrations (Flyway and Liquibase)
• Auditing (@CreatedDate, @LastModifiedBy)
• Soft deletes
• Multi-tenancy
• Multiple datasources
• First-level and second-level caching
• Database indexing and query optimization
• Alternatives: jOOQ, MyBatis
• Spring Data R2DBC (reactive)
• Spring Data REST (optional)

Databases

• PostgreSQL
• MySQL
• Microsoft SQL Server
• MongoDB
• Redis
• Elasticsearch / OpenSearch
• Cassandra (optional)

5. Spring AOP (Aspect-Oriented Programming)

• Aspect-Oriented Programming fundamentals
• Aspects
• Advice
• Pointcuts
• Join points
• @Aspect
• @Before
• @After
• @Around
• Custom annotations
• Logging aspects
• Performance monitoring
• Audit logging
• Exception tracking
• Proxy-based AOP (JDK vs CGLIB)
• Self-invocation limitations

6. Spring Boot Testing

• JUnit 5
• Mockito
• AssertJ and Hamcrest
• Unit testing
• Integration testing
• @SpringBootTest
• @WebMvcTest
• @DataJpaTest
• @JsonTest
• @RestClientTest
• @MockBean and @MockitoBean
• MockMvc
• WebTestClient
• TestRestTemplate
• REST API testing
• Repository testing
• Security testing
• Exception testing
• Testcontainers (Postgres, Kafka, Redis)
• Database integration testing
• Test profiles and test data management
• Test coverage (JaCoCo)
• Contract testing (Spring Cloud Contract, Pact)
• WireMock
• Mutation testing (PIT, optional)
• TDD practices

7. Spring Boot Caching

• Caching fundamentals
• Spring Cache Abstraction
• @EnableCaching
• @Cacheable
• @CachePut
• @CacheEvict
• Cache managers
• Cache invalidation strategies
• Redis caching
• Caffeine caching
• Distributed caching
• Cache expiration (TTL)
• Cache synchronization
• Cache consistency
• HTTP caching (ETag, Cache-Control)

8. Spring Boot Messaging and Event-Driven Architecture

• Spring Events
• Application events
• Event listeners
• @EventListener
• Asynchronous event processing
• Spring Events vs external messaging
• Spring AMQP
• RabbitMQ integration
• Spring for Apache Kafka
• Kafka producers and consumers
• Consumer groups
• JMS / ActiveMQ
• Spring Cloud Stream
• Message serialization and deserialization
• Message acknowledgment
• Retry mechanisms
• Dead Letter Queues (DLQ)
• Message ordering
• Idempotency and exactly-once semantics
• Event-driven architecture
• Eventual consistency
• Transactional Outbox Pattern
• Saga Pattern

9. Spring Cloud and Microservices

• Monolith vs microservices trade-offs
• Microservices architecture
• Spring Cloud fundamentals
• Service discovery (Eureka, Consul, Kubernetes-native)
• API Gateway
• Spring Cloud Gateway
• Centralized configuration
• Spring Cloud Config
• Inter-service communication
• OpenFeign
• RestClient
• WebClient
• Load balancing (Spring Cloud LoadBalancer)
• Circuit breakers
• Resilience4j
• Retry mechanisms
• Rate limiting
• Bulkhead pattern
• Distributed tracing
• Distributed transactions
• Saga Pattern
• Service-to-service authentication (mTLS, token relay)
• API composition
• CQRS
• Event sourcing
• Microservices observability

10. Spring Boot Scheduling and Background Jobs

• Spring Task Scheduling
• @Scheduled
• @EnableScheduling
• Fixed-rate scheduling
• Fixed-delay scheduling
• Cron expressions
• Distributed scheduling (ShedLock, Quartz)
• Asynchronous execution
• @Async
• Thread pools
• Task executors
• Spring Batch
• Batch processing
• Job configuration
• Job parameters
• Job execution
• Step configuration
• Chunk-oriented processing
• Job restartability
• Job monitoring

11. Spring Boot Email and Notifications

• Spring Mail
• SMTP configuration
• Sending plain-text emails
• HTML emails
• Email templates
• Thymeleaf integration
• Email attachments
• Asynchronous email delivery
• Email retry mechanisms
• Notification services
• SMS integration
• Push notification integration

12. Spring Boot Observability and Monitoring

• Application logging
• SLF4J
• Logback
• Log levels
• Structured logging
• Correlation IDs / MDC
• Spring Boot Actuator
• Health checks
• Custom health indicators
• Securing Actuator endpoints
• Application metrics
• Micrometer
• Prometheus
• Grafana
• Distributed tracing
• OpenTelemetry
• Zipkin
• Jaeger
• Centralized logging
• ELK Stack / Loki
• Application performance monitoring
• Readiness and liveness probes
• Error tracking
• Audit logging
• Alerting basics
• Spring Boot Admin (optional)

13. Spring Boot Configuration and Secrets Management

• application.properties
• application.yml
• Externalized configuration
• @Value and environment abstraction
• Environment variables
• Configuration profiles
• Profile-specific configuration (application-dev.yml)
• Configuration properties (@ConfigurationProperties)
• Configuration validation
• Custom configuration
• Secrets management
• Environment-specific credentials
• Spring Cloud Config
• HashiCorp Vault integration
• AWS Secrets Manager
• Kubernetes ConfigMaps
• Kubernetes Secrets
• 12-factor app principles

14. Spring Boot API Documentation

• OpenAPI specification
• Swagger UI
• Springdoc OpenAPI
• API documentation
• Request and response schemas
• API descriptions
• Authentication documentation
• API versioning
• API contracts
• Error response documentation
• Spring REST Docs

15. Spring Boot File and Storage Management

• Multipart file handling
• File uploads
• File downloads
• File validation
• File size restrictions
• Local file storage
• Cloud storage integration
• AWS S3
• Azure Blob Storage
• Google Cloud Storage
• MinIO
• File metadata management
• Streaming large files
• Document processing

16. Spring Boot Integration

• REST API integrations
• Third-party API consumption
• Spring RestClient
• RestTemplate (legacy)
• WebClient
• HTTP Interface clients (@HttpExchange)
• OpenFeign
• External service authentication
• API keys
• OAuth2 client credentials
• Request and response interceptors
• Timeout configuration
• Retry handling
• Error handling
• gRPC basics
• SOAP web services
• Spring Web Services
• SFTP integration
• Legacy system integration
• Payment gateway integration

17. Spring Boot Reactive Programming

• Reactive programming fundamentals
• Project Reactor
• Mono
• Flux
• Reactive Streams
• Spring WebFlux (annotated and functional endpoints)
• Reactive controllers
• Reactive repositories
• Reactive MongoDB
• Reactive Redis
• Reactive security
• Backpressure
• Error handling in reactive pipelines
• Reactive testing (StepVerifier)
• Non-blocking I/O
• Differences between Spring MVC and WebFlux
• WebFlux vs virtual threads

18. Spring Boot Deployment and DevOps

• Maven
• Gradle
• Dependency management
• Maven lifecycle
• Build profiles
• JAR packaging (executable and layered JARs)
• WAR packaging
• Docker
• Dockerfiles
• Buildpacks (spring-boot:build-image)
• Docker Compose (including Spring Boot Docker Compose support)
• Containerization
• Kubernetes fundamentals
• Deploying Spring Boot to Kubernetes
• Helm
• CI/CD pipelines
• Jenkins
• GitHub Actions
• GitLab CI/CD
• Cloud deployment
• AWS deployment
• Azure deployment
• GCP deployment
• Linux server administration
• Nginx
• Reverse proxies
• SSL/TLS configuration
• Environment configuration
• Zero-downtime deployments
• GraalVM native images and AOT
• Static analysis (SonarQube, Checkstyle, SpotBugs)
• Dependency vulnerability scanning (OWASP Dependency-Check, Dependabot)

19. Spring Boot Performance Optimization

• JVM fundamentals
• JVM memory management
• JVM tuning and container memory settings
• Garbage collection
• Thread management
• Connection pooling
• Database query optimization
• Hibernate performance tuning
• Lazy loading optimization
• Caching strategies
• API response optimization
• Compression for large payloads
• Pagination
• Asynchronous processing
• Profiling
• Load testing (JMeter, Gatling, k6)
• Stress testing
• Memory leak detection
• Database connection monitoring
• Thread pool tuning

20. Spring Boot Architecture and Design Patterns

• Layered architecture
• Controller-Service-Repository pattern
• Clean Architecture
• Hexagonal Architecture
• Domain-Driven Design (DDD)
• SOLID principles
• Dependency inversion
• Separation of concerns
• DTO pattern
• Repository pattern
• Factory pattern
• Strategy pattern
• Builder pattern
• Adapter pattern
• Observer pattern
• Dependency injection patterns
• Modular monolith architecture
• Microservices architecture
• CQRS
• Event sourcing
• Saga pattern
• Idempotency
• API gateway pattern
• Circuit breaker pattern
• Outbox pattern
• Multi-tenancy strategies
• GraphQL API design

21. Spring Boot Advanced and Specialized Modules

• Spring Batch: enterprise batch processing
• Spring Integration: enterprise system integration
• Spring Authorization Server: building OAuth2 authorization servers
• Spring Session: distributed session management
• Spring LDAP: LDAP authentication and directory integration
• Spring GraphQL: building GraphQL APIs
• Spring for Apache Kafka: Kafka integration
• Spring AMQP: RabbitMQ integration
• Spring Modulith: modular monolithic applications
• Spring REST Docs: API documentation through tests
• Spring Shell: command-line applications
• Spring Web Services: SOAP web services
• Spring AI: LLM integration, vector stores, RAG
• Spring Statemachine: managing complex state transitions
• Spring Data REST: exposing repositories as REST endpoints
• Spring Cloud Stream: event-driven microservices
• Lombok (and its trade-offs)
• Internationalization (i18n)

Suggested Learning Order

• Foundation: sections 0 to 1
• Build APIs: sections 2 to 4
• Make it safe and correct: sections 3, 5 and 6
• Make it fast: sections 7, 10 and 19
• Production-ready: sections 12, 13 and 14
• Integrate and scale out: sections 8, 9, 11, 15 and 16
• Ship it: section 18
• Design like a senior: section 20
• Specialize: sections 17 and 21