Backend Development: Spring Boot

Variables, types, control flow, OOP (classes, inheritance, polymorphism, interfaces), collections, streams, lambdas, and Java 21+ features.

• JetBrains Academy: Java Developer Track (free trial)coursefree
• Baeldung: Java Tutorials (free)articlefree
• Cay Horstmann: Core Java Vol 1 (book)coursepaid

• Generics and bounded wildcards
• Collections: ArrayList, HashMap, LinkedHashMap
• Functional: Stream API, lambda, method references
• Java 21: records, sealed classes, pattern matching

Project structure, dependency management, build lifecycle, plugins, and multi-module projects.

• Maven Getting Started Guide (official)docfree
• Gradle User Manualdocfree

• Multi-module Maven project
• Gradle build with custom tasks
• Dependency scopes: compile vs test vs provided

Git branching strategies, Docker for local dev, IntelliJ IDEA setup, and code quality tools (Checkstyle, SpotBugs).

• Pro Git (free book)docfree
• Docker Official Docsdocfree

• Conventional commits + PR workflow
• Dockerfile for a Java app
• Docker Compose: app + PostgreSQL

IoC container, dependency injection, auto-configuration, Spring Boot starters, profiles, properties, and actuator.

• Spring Boot Official Docsdocfree
• Spring Boot in Practice (Manning)coursepaid
• Baeldung: Spring Boot Seriesarticlefree

• Spring context: @Component, @Service, @Repository
• Constructor injection vs field injection
• Profiles: dev vs prod configuration
• Actuator: health, metrics, info endpoints

@RestController, @RequestMapping, request/response DTOs, validation (@Valid, Hibernate Validator), exception handling (@ControllerAdvice), and OpenAPI/Swagger.

• Spring Web MVC Docsdocfree
• Baeldung: REST with Spring Tutorialarticlefree
• OpenAPI / springdoc-openapi Docsdocfree

• CRUD API: User resource with all 5 verbs
• Global exception handler: consistent error body
• Request validation with @Valid + custom constraints
• Swagger UI auto-generated from annotations

JPA entities, repositories, JPQL, native queries, pagination, transactions, N+1 problem, and database migrations with Flyway.

• Spring Data JPA Docsdocfree
• Flyway Docsdocfree
• Vlad Mihalcea: High-Performance Java Persistence (book)coursepaid

• OneToMany + ManyToMany entity mapping
• Flyway migration: baseline + V1__init.sql
• Pagination with Pageable
• Solve N+1 with @EntityGraph or JOIN FETCH

Spring Security filter chain, authentication, authorization (RBAC), JWT tokens, OAuth2 resource server, CSRF, and CORS configuration.

• Spring Security Reference (official)docfree
• Baeldung: Spring Security (series)articlefree

• JWT sign + verify + refresh token flow
• Method security: @PreAuthorize roles
• CORS: allow frontend origin
• OAuth2: login with Google

JUnit 5, Mockito, @SpringBootTest, @WebMvcTest, @DataJpaTest, TestContainers for real DB tests, and WireMock for external service mocking.

• JUnit 5 User Guidedocfree
• Testcontainers for Java Docsdocfree
• Baeldung: Testing in Spring Bootarticlefree

• Service layer: unit test with Mockito
• @WebMvcTest: controller slice test
• Integration test: Testcontainers PostgreSQL
• >80% coverage on service + controller layers

Service decomposition, Spring Cloud (Eureka, Config Server, Gateway, Feign), resilience (Resilience4j), and event-driven inter-service communication with Kafka.

• Spring Cloud Docsdocfree
• Sergey Kargopolov: Spring Boot Microservices (Udemy)coursepaid

• Service registry with Eureka
• API gateway routing + rate limiting
• Circuit breaker with Resilience4j
• Async communication via Kafka

Spring Boot Actuator + Micrometer, Prometheus metrics, Grafana dashboards, structured logging with Logback, Docker containerisation, and Kubernetes deployment.

• Spring Boot Actuator Docsdocfree
• Micrometer Docsdocfree

• Expose custom Micrometer metric
• Grafana dashboard: JVM heap, request rate, errors
• Multi-stage Dockerfile: build + runtime JRE
• Deploy to Kubernetes with ConfigMap + Secret