Spring Boot From Zero

Learn Spring Boot the way it's actually used: what auto-configuration really does, dependency injection and beans, building a REST API, configuration and profiles, persistence with Spring Data JPA, the service layer and validation, error handling, testing, security, and shipping to production. Mental-model-first, magic demystified.

1. What Spring Boot Is & Your First App Spring is the giant toolbox; Spring Boot is Spring with auto-configuration, sensible defaults, and an embedded server so you go from zero to a running web app in minutes.
2. Dependency Injection & Beans The heart of Spring: why dependency injection exists, what the IoC container and a bean actually are, declaring beans with @Component/@Service, and constructor injection over field @Autowired.
3. Building a REST API: Controllers Turn a Spring app into a real HTTP API: @RestController, GET/POST mappings, path variables and query params, JSON request bodies, ResponseEntity for status codes, and how a request actually flows.
4. Configuration & Profiles How Spring Boot reads externalized config: application.yml, @Value and @ConfigurationProperties, the precedence order that lets one jar run anywhere, profiles per environment, and keeping secrets out of your code.
5. Persistence with Spring Data JPA Map a Book object to a database table with JPA, then let Spring Data generate a whole repository for you — save, find, derived queries — and learn where the ORM magic stops and you still owe the database your attention.
6. The Service Layer, DTOs & Validation Give your API a spine: a thin controller, a transactional service holding business logic, DTOs that decouple the API from the database, and Bean Validation that rejects bad input before it ever reaches your code.
7. Error Handling Done Right Turn raw exceptions into honest HTTP responses: per-controller @ExceptionHandler, app-wide @RestControllerAdvice, the right status code for each failure, and one consistent error body with Spring's ProblemDetail.
8. Testing Spring Boot Apps Cash in the layering from Phase 6: unit-test the service with a mocked repository, slice-test the web layer with @WebMvcTest + MockMvc and the JPA layer with @DataJpaTest, then go end-to-end with @SpringBootTest and Testcontainers.
9. Security with Spring Security Spring Security is a chain of servlet filters every request passes before your controller. Master that one idea and the rest — authN vs authZ, the SecurityFilterChain bean, password encoding, and stateless JWT — stops being voodoo.
10. Production: Actuator, Packaging & Deployment Take a Spring Boot app from 'runs on my machine' to production: Actuator health and metrics endpoints, building a self-contained fat jar, prod config, Dockerizing, and where it actually runs.
11. Where to Go Next You can build a layered, tested, secured REST API and deploy it. Honest signposts to where Spring goes from here — microservices, reactive, messaging — plus what to build.